Introduction to Evolution PDF

hi everybody and welcome back to miss angler's biology class i am miss angler and in today's video we are going to do an introduction to evolution this is a new series of videos that are going to replace my old videos and i'm going to update these ones now with you now if you're new here don't forge...

hi everybody and welcome back to miss angler's biology class i am miss angler and in today's video we are going to do an introduction to evolution this is a new series of videos that are going to replace my old videos and i'm going to update these ones now with you now if you're new here don't forget to give this video a thumbs up and subscribe and turn your notifications on because i post every tuesday and thursday for grade 8 to 12 biology also if you're new here and you're thinking about joining my membership because you would like to get 80 or more in your final exams don't forget to click the join button that you can find on my home page there you'll get access to extra videos my notes live lessons with me and so much more now as i mentioned earlier this particular video is replacing my older videos on evolution it's just an updated version so let's look at first of all this diagram in front of us which is called a phylogenetic tree you need to be very comfortable in reading these when we go through evolution because it's how we express evolution which is quite abstract and we we express it in this physical diagram way and essentially a phylogenetic tree is showing us how organisms have evolved over time and each of these branches that we see here on the diagram represent a point at which something dramatic happened on earth and it led to a group of organisms arising in other words they descended from somebody else and so every time there's like a little notch in our little tree over here it represents also a common ancestor some particular organism was very key in evolution that we have left behind and that we have created a newer version of that organism or that old common ancestor could still even be around today now the last basic thing we need to know about phylogenetic trees is the fact that they are showing us essentially a timeline we're starting from the oldest organisms and we're moving upwards to the newer organisms and also the more complex organisms generally not always the case now in this diagram there isn't a time scale but please know in exams there will be and generally it is counted in mya or millions of years ago and they will ask you questions like when did plants arise or when did slime molds arise when did they appear and so what you would do is you would look at for example slime molds over here you would look at where do slime molds intercept with the timeline and then you'd be able to tell them how many millions of years ago but that's the basics of how to use a phytogenic tree now we're going to briefly look at the evidence for evolution and for your tests and exams you need to know your four pieces of evolution which is fossil records biogeography descent with modification and genetics sometimes this is a question where they will literally ask you name two types of evidence used for evolution and these are the four that you can give now if they don't ask for an example please don't give an example and what i mean by that is if they say name two types of evidence well you have four to pick from here so only use these four but if they said name two types of genetic evidence for evolution then you're going to say something like mitochondrial dna or dna and rna you're going to actually give examples of each of these now the first piece of evidence is the fossil record and the fossil record shows us three important things that we will need to know for the exam the fossil record shows us that organisms over time become more complex in other words their structures are more complex they become more diverse in other words we started off with simply being a simple group of cells like protists and bacteria and now we have arms and legs and eyes and so many complex tissues so we've become complex and we've become diverse meaning we don't just have one kind of cell or one kind of bacteria we have millions of different kinds of microorganisms we have thousands of different kinds of birds and reptiles and mammals and so what the fossil record shows us is that with time organisms have become more complex and they've become more diverse the third and final thing that the fossil record supports when it comes to evolution is what we call transitional fossils transitional fossils are fossils that show organisms that seem to be an intermediate or a mixture and examples of these are things like the archaeopteryx which is a mixture between a bird and a reptile it has characteristics that we see in both groups and so we consider it a transitional fossil and what these transitional fossils show us is organisms that sit somewhere in between the two that allow us to then draw out these family trees that we see alongside you these phylogenetic trees that we have here now some of these fish may no longer be around for example all of the fish here that have the cross next to them are extinct however they are all important key transitional fossils that we have found that then allow us to draw a full family picture the remaining fish here the rayfin fish lungfish and living tetrapods those are the organisms we still see today and we have their earlier onset ancestor fossils available to us  now in the exam you are going to be expected to explain what a transitional fossil is so you need to be prepared to explain that it is a fossil that exhibits physical structures or phenotype similarities that make them an intermediate in other words they have a mixture of two different phyla or two different groups of organisms the next piece of evidence is biogeography and as the name suggests it references how geography of the land has influenced the organisms that live on it and what you're looking at here is when all of these southern continents were still attached to one another and you see areas of fossils that are shared amongst these continents now this is only possible if at one point all of the continents were attached to one another and this supports evolution because what it says is there's no way that an organism could evolve to look and behave a certain way if it's found in multiple locations with massive seas and oceans in between the land masses there'd be no way for this organism to look the same if it was divided into different populations across giant oceans and as an example to illustrate this if we looked at the listosaurus it was found across the african continent over madagascar india and then antarctica this is all where we find this fossil now the fact that we can find the exact same fossil for the exact same set of years it only leads us to believe that when the listosaurus first originated and evolved and appeared in these regions the land was joined together which supports evolution because it tells us that when the lystosaurus was alive and it was adapting and evolving it would have had to have done so over the same land mass because if the land mass separated and took the listosaurus with it which it to some extent did when india and africa and the antarctic separated those organisms would start to experience evolution independently because their populations would be too far away from each other for them to interact or to interbreed with each other the next piece of evidence is modification with descent and as the name suggests it refers to how structures and organisms have modified over time and as they've descended from their common ancestor and we have a perfect example of this when we look at the left hand picture showing something called the pentadactile limb it is essentially the limb or the arm bone in most of these organisms that is a similar structure you'll notice that they've highlighted the bones that are the same the humerus the carpals metacarpals the phalanges but you'll notice that they have changed slightly they have modified and their modification represents a need to change in order to be suited to their environment now remember these organisms didn't want to change they didn't force themselves to change and we're going to go into more detail about actually how does this come about when we look at natural selection but when we talk about modification with descent we are talking about homologous structures and these are structures like limbs organs skeletal structures that are similar in structure but they serve different purposes and the fact that they're so similar in structure can only point to the fact that they evolved from a common ancestor and therefore they're all descendant now this alternate picture i have on the side here is a modification with the scent but this time moving towards modern elephants and what it indicates is many different uh groups of subspecies of evelephants and also ancestors of elephants so here is the current african elephant and the current asian elephant at the very end they are both alive currently but everyone beyond that or should i say below that no longer is alive they are extinct however what this diagram shows us is it shows us an important aspect of common descent which is a common ancestor now common ancestors they are key in showing genetic links and more common ancestors means that they are more closely related now what does that mean for us in this diagram well common ancestors represent these individuals here these little points and these common ancestors all the way along wherever we see a little branch off represent a key change something that happened in the environment that caused a branch off to happen and these fossils of all these other predecessors these primitive elephants if that's what you want to call them they show us that we have modified the elephant over time some of the elephants have survived until this point which is where we see our current two elephants now but other elephants have become extinct for a variety of reasons it may be because of their habitat has disappeared or perhaps they've become extinct due to ice ages like the mammoth but what we see here is modification over time and you are descending to where you are now in other words what groups are still present on earth now the final piece of evidence is genetics and when we speak about genetics we are speaking about two major aspects about what genetics can share with us and the diagram i have a very simple outline here of all of the percentage uh genes that we share with other animals  um we share 99.5 of our genes with chimps 75 of our genes are shared with chickens even 60 of your dna right now is exactly the same as a fruit fly and so how does genetics support evolution well the first thing it does is it shows us that genes and common ancestors must go hand in hand we have to have a common ancestor in order to share genes and so all organisms have dna or rna in some fashion which means we must be related to each other there's no alternate and the fact that all organisms genes cone for the same protein in other words the way in which a mouse makes muscle is the same way a chicken makes muscle the same way a human makes muscle we all make these same structures in exactly the same way and that means we have the same genes the second thing that genetics shows us is how related we are and organisms are based on their relatedness due to how much chromosomal or how much mitochondrial dna they share so the more chromosomal or the mitochondrial dna we share the more closely related we are whereas the fewer chromosomal or mitral chondrial dna we share the less we are related the more distant we are and so that's how we calculate relatedness we see how much we have in common and then how much we have that is different and if we have more different then we are obviously further related in other words our common ancestor was much much further back and that's basically what we see here in this percentage of genes it means that our ancestor with fruit flies was much older than that of the chicken the mouse and the chimp in other words our common ancestor with a mouse is much closer to us than the common ancestor between humans and fruit flies now that we've looked at the evidence for evolution the final key piece before we look into well how does evolution actually like happen we need to look at one more thing and that is variation there is variation at a species level in other words you can see variation between individuals but there's also variation amongst a entire population and so that means we need to look at all the differences between the individuals as well as the differences within populations and these variations that we see in our genes and our genetics helps evolution take place now these two words that i'm about to go through now you must know off by heart for your exams and you need to put some key words in their definitions if they ask for it the first one is species now a species is a group of individuals that are able to breed amongst themselves and produce viable offspring viable means that their offspring are fertile they can make more of themselves an example of that would be like two horses reproduce and they make a fertile offspring a fertile baby horse however if you mix a horse with a zebra which you can do they will not produce viable offspring in other words the mixture between the horse and the zebra the zos will not be able to make more babies on its own each time you would have to have a horse and a zebra um combining together the second word we need to know is population now it's slightly different to species you've got to see the nuances and the difference a population is a group of individuals belonging to the same species who occupy a particular habitat it means they live in a particular place at the same time and are able to reproduce and again produce viable offspring the same time and same place is important so the particular habitat and the time is important because you can have a population of elephants in kenya and then you can have a population of elephants in south africa and you have got to know which population you were talking about they are the same species they're just in two different locations in two different perhaps time sets but these two populations could still meet one in kenya and one in south africa and they could still reproduce with each other now when it comes to the variation that we see in these species that we have mentioned now there are two types if we're talking about variation in a species you can have continuous variation or you can have discontinuous variation and it's pretty self-explanatory by these pictures but essentially continuous variation means there is a continuous or endless amount of possible combinations and lots of in-betweens and eye color is a perfect example of that these are just some of the eye colors that we see in humans but anyone can be a mixture of these and even newer colors that aren't on here right now can appear especially if we're mixing our eye colors together so it's continuous on the other side we have the peppered moth and it shows discontinuous variation because there's only two options it's either a black moth or a white moth and they're both the same species however they just come in two colors it's discontinuous because there's no in-betweens now as always i like to end off the lesson with a terminology recap and you can use these words for flash cards and to study from for exams we looked at the evidence that was used for our evolution and we've got fossil evidence which shows of course complexity and diversity changing  we then looked at biogeography which was the locations in which we find those fossils and how those prove that they evolved together at the same time we have descent with modification which is the change or the modification of a organism's structure and that shows that they originated as one structure and it's changed over time in different animals for for different reasons and those particular structures are often called homologous structures as i showed you with that arm that we can see in many different mammals but also birds and amphibians then we looked at genetics which showed us how our similarities in our dna link us together and how much we share um it makes us more or less related we spoke about common ancestors who are organisms that are shared in our family tree and they represent organisms that have um characteristics shared by our ancestors that we don't necessarily see today alive but they were alive at one point and they exhibit physical characteristics that are in us but also in other relatives we spoke about variation which is the differences within ourselves and in our genes and we looked at variation in a species versus a population and we looked at those definitions i forgot to mention continuous and discontinuous variation you remember that continuous variation speaks about like eye color and height with lots of in-betweens whereas discontinuous speaks about our either ors either you have it or you don't we saw that in the peppered moths they're either black or they are white and these kinds of variation leads to opportunities for evolution to take place now if you like this video don't forget to give it a thumbs up and subscribe and i will see you all again soon bye  hi everybody and welcome back to miss angel's biology class i am miss angler in today's video we are going to be taking a look at hominid evolution now it's important at this point of the video if you haven't watched my human and ape similarities and differences in the skeleton you should go back now and watch that video i have linked it above so you should go watch that otherwise we're going to dive into how to tell the difference between all the hominid skulls their skeletons how to look for key features as well as what to expect in exam questions on this particular topic because it seems like there's a lot you need to know but actually i'm going to show you that you don't really need to know too much about all of them but rather you need to know the trend and the change of the skeletons over time now if you like this video make sure to give it a thumbs up and make sure you're subscribed with your notifications turned on because i post new videos every tuesday and thursday and if you're in matrick and you're thinking about getting an a in the finals make sure that you are a member you get access to my study guide as well as members only live lessons and videos now to start off i need to point out some key skills that you're going to need in order to be really good at this topic the first thing you need to be able to do is you're going to have to be able to identify key features on skulls or skeletons and you're going to need to tell me why those changes those developments were important the next important skill that you are going to need for your exams and tests is you're going to need to be able to show how skulls or skeletons have progressed with time and you're going to have to show a trend in other words how something has changed shape over the course of its evolution so we're going to start off first of all with the skull differences now there are some really important skull differences that you need to know the first one is linked to bipedalism and bipedalism is associated with the foramen magnum now if we look at the diagram on the left hand side i'm going to highlight the foramen which is the opening into the skull where the spinal cord enters towards the brain and you'll notice that his position is different in each of these organisms now this particular picture has been arranged from oldest to newest skull starting from the top with the oldest and the newest at the bottom but i want you to notice that the first organism has its foramen more backward the middle organism has moved slightly forward and then the human has it way more forward now a word that we really really want to avoid in tests and exams is the word central or centrally please do not use this word when you talk about the foramen magnum you don't want to use that word instead what you want you should you should be using is more forward or if you're trying to describe the fact that um it's further back then you would just say more backwards but you don't want to use the word centrally when we're discussing the foramen so every time you think of bipedalism i want you to think about where is the foramen magnum where is its location and that then tells us it whether or not the organism was bipedal so the more forward the foramen magnum is the more bipedal the organism was and that means that they were upright and upright posture walked on two legs and that's because they wanted to hold all their body weight over the center of their body the next thing i want to talk about is the brain size now the brain size is linked to how big the cranium is on the inside right so i've got this picture here on the right hand side and you'll see alongside it has a number and the word or the letters cc basically cc means cubic centimeters and it's referring to how much like liquid or fluid you could fit in the center now you'll notice a collection of five skulls here and they're increasing in capacity and when there's an increase in brain size there is an increase in intelligence now the last thing i want to highlight that we can see in the skull is going to be the canines and specifically the size of the canines now this is really important so if we look at either one of these diagrams we'll be able to see that the canines are actually changing size and in some of these it's actually really difficult to be able to see them quite clearly but that's really important because you need to see again focus on the trend of the canine the canines were getting smaller with time so they become smaller over time and that's one way you can look at a skull and go oh that's a very old skull it's got really large canines that skull's got much smaller canines so it must be newer and you again may be asked to arrange skulls from oldest to newest depending on these features so you've got to know what you're looking for so the next piece of evidence and physical characteristic we need to look at when ordering our skulls in the hominids is prognathism and prognathism refers to the lower jaw and the size of the lower jaw as well as the shape of the face that it creates now in gorillas they have a really large prognathus jaw we can see that here in homo erectus one  of our family members it's it has reduced in size but still prognathus whereas humans um it has reduced greatly and the effect it has is also on the slope of our face you'll notice that the gorilla has quite a sloped face the homo erectus has a lesser sloped face but unfortunately this little slope happening over here means that it still has a prognathus jaw whereas humans have a very flat face which means we are non-prognathus now again this is where terminology is so important when you are talking about the skull as seen in the gorilla and in homo erectus we are going to need to use the word that it is a prognathus jaw but you don't get less prognathus so that's really key please don't use the word less you can either have a prognathus jaw or if you are a homo sapien like us then you have a non-prognathus jaw and it's important that you know how to use the difference because in an exam that is all they will accept now the next important feature that you need to be able to explain and identify is going to be the palette shape now the palette shape is quite easy to tell the difference because it's changing shape from a more rectangular long almost like a snout like a long nose shape and it goes from that rectangular shape to being slightly more arch like a u and then finally what we would call a parabolic arch so it's way more arch and it flares out at the bottom now this shows a change in diet it shows a change in the actual face structure and so what you will be asked to do is you might get these unlabeled and you would have to say which one's the chimp which one's the australopithecus and which one is the modern human and basically you're going to use the shape to help you identify them you can also use this other structure over here called the diastema you will notice that it is present in both the chimpanzee over here but also to a slightly lesser degree in the australopithecine and a diastema is the little empty space that you would have next to your canine so that your upper canine can lock into your lower canine and that's what you see with like animals with really large teeth their canines sit next to each other and they almost like sit um outwards so they're more prominent and and and more scary looking and that's another reason why we've also lost the size in our canines is we don't use them anymore to tear meat to uh to tear raw vegetation everything is cooked we don't need to scare each other off anymore with our teeth and so the need for that has disappeared and our canines have also gotten smaller because of that the next important facial feature that we need to focus on again and you can use this to rank your skulls from oldest to newest it's going to be the cranial ridge and the brow ridge not the same thing and sometimes the cranial ridge is also known as the sagittal crest so let's start off with that one the cranial ridge now i've got a human a gorilla and a chimpanzee here and essentially what you can see if you know what you're looking for is the cranial or the sagittal crest is really prominent on our gorilla you'll notice that humans don't have one we're just nice and smooth on the top and our chimpanzee doesn't have one either actually and that's to show that out of these three individuals who's more closely related well the human and the chimpanzee another one that you might see is an australopithecine and they would have a slightly reduced cranial ridge or sagittal crest and remember that's what you're trying to do you're trying to show how things go from being the biggest to the smallest like the canines or if we're talking about the cranium we're talking about how the cranium started small and then got bigger with time now this other key key feature that i want you to look out for is the brow ridge and again i'm going to start with the gorilla because it's really prominent this is the brow ridge over here and it's nice and easy to see it in the front of the skull you'll notice that humans barely have one it's really really small and reduced whereas the chimpanzee on the other hand has quite a prominent brow ridge now the brow ridge is linked to the jaw bone and the chewing muscles as well as the cranial ridge because that's where all your chewing muscles attach to the top of your head so if they're asking questions like why did the bra ridge disappear why did the cranial ridge disappear it's because we started cooking our food we chewed our food less and so we didn't need as large muscles to do so and then we started using our mouth for other things which would be like speaking and language now the final key key key skeletal structure that i need you to know and be able to tell how it changes over time is going to be the pelvis now the pelvis links also to bipedalism so this is also important to explain that but essentially what you need to be able to show is how the pelvis has changed over time again you may be given a whole bunch of pelvises and that are not labeled and you have to say which one is the human and which one is the chimpanzee and which one is the transitional animal in other words the animal that is transitioning from one hominid to the next in this example it  would be the australopithecus africanus but let's say it's not labeled what are you going to look for right so the key and important thing that we need to look for is linked around the uh length in terms of how long it is but also how wide it is and so that's the thing that we are going to look for now in chimpanzees they have very long and they have very narrow pelvis the australopithecus africanus on the other hand is less narrow but not completely broad like ours and it is reduced in length right it's gotten a little bit shorter but not as much as ours our pelvis and our pelvic bone on the other hand is what we would describe as being broad which means that it is wide like this and it is short and if you compare it to the chimpanzee it is very very much so short because if we were to like draw them evenly if they were in terms of their height and if you measured from the bottom here to the top and the bottom here to the top the chimpanzee is much much much longer and so that's what you are looking for you are looking for organisms that show change over time and they could be what we consider an intermediate which is what we see we see here with the australopithecus now i want to show you some examples of like pictures you might be given so that you know what to expect if you get this in an exam and what they're going to ask you now the first thing they may ask you in an exam is a question based off of a phylogenetic tree like the one we see on the left hand side here and essentially they might ask you how many millions of years ago did australopithecus africanus appear so you've got to go on to your diagram and you've got to measure along and you sort of like draw a line going across here you see where it intersects and you give the ur right other things might be like who's more closely related to each other uh neanderthals to homo sapiens or homo sapiens to homo erectus and you're going to have to explain that well homo sapiens uh only share let's see one [Music] two three four five common ancestors with homo erectus but homo neanderthals let's change the color one two three four five six common ancestors which means they're more closely related now by the way if you weren't sure how i did this little thing like how did i know well every time the branches branch out that's a little common ancestor and so that common ancestor counts as a little individual that we must count and the more you have the more you're related to each other there are many other things they can ask you which can include names of famous and well-known fossils and so for ardopithecus there's really only one we need to know which is adi for australopithecus affarensis there is lucy and the latolli footprints for a africanus there's the taong child mrs players and littlefoot and yes you will also need to know who discovered them and in what country they were discovered so what to expect in exams i've got two different pictures alongside here and i'm going to start with a picture on the right hand side now you get this picture in the exam and the first question is which organism is the human and let's say they have letters because that's also going to make this easier so this is a this is b and this is c so which one is the human now right off the bat i already know that a is going to be the human why let's say that's the follow-on question they say give two visible reasons why so we've got a lot of visible reasons that we can pick on and i'm gonna highlight some number one you can talk about the foramen magnum and its location number two you can talk about the shape of the pelvis if you compare them to the other three the next thing is that you can compare the size of the cranium it has the largest cranium out of all of them you can also talk about the reduced canines so there's a lot that you can actually talk about just by looking at the skeleton the next question you might interact with is they're going to ask you to order the skulls from oldest to newest in other words who is the least related and who is the most related and in this instance i'm going to say it is going to be c then b then a now how did i get that well again i looked at the skeleton the first thing that gives away the clue is as always the foramen magnum and you'll notice that the foramen magnum is moving more forward with each of these until we get to the human the next thing again and you should be able to provide this reason is the shape of the pelvis the pelvis started long and narrow it got broader and wider and shorter until it was completely broad and short you could even actually talk about the teeth as well you will notice actually let's remove that you will notice that the canines are really large in the chimpanzee they are reduced in the australopithecine and then they are barely visible in the humans that's another way i knew how to actually rank these the follow-up question that can also go with this everybody is something like this using the evidence in the diagram explain how changes to the skeleton supported bipedal movement now it's important to know this everybody the center diagram this one here is not useful to explain bipedalism nothing  about the cranium nothing about the teeth is going to help you explain why we walk on two feet the most important things here is going to be the pelvis so you're going to discuss the pelvis shape and the fact that it's wide and short and it provides support and holds the body upright with all the weight evenly distributed and the second thing you want to talk about is the foramen magnum being more forward which means that it supports an upright body movement it evenly distributes the weight and it allows the spine to be more flexible and that's what you are going for when you're describing this in the exam now if we move to the other diagram again you could have six skulls that you need to arrange now the key things that i would use if they said to you arrange these six goals from oldest to newest what are you going to do so there are key features that you can use to arrange them from oldest to newest the first thing you're going to look for is the brow ridge remember which is this bit up here now the brow ridge actually reduces over time it gets smaller so what do you need to do you need to arrange these skulls from biggest brow ridge to smallest brow ridge the next thing that i would look at which is very easy is how big the cranium is so we need to arrange these skulls from the smallest cranium to the largest cranium the next and most easiest feature to look for is the teeth the canines again you're going to arrange these skulls from the largest canines to the smallest canines and those three things are probably the easiest to arrange them from oldest to newest hominids in an exam the good news is that they very rarely give you one skull they always give you another skull to work with and compare to and that makes us much easier now as always i'd like to finish off my lesson with a terminology recap please use these words when you're describing how hominids have changed over time and explain how those changes have impacted how we walk on two legs how we cook our food um how our structures in our body have changed over time those pieces of evidence that i've just run through now are really important and you must use the terms speaking of which bipedalism is again the most important term when we talk about hominids so you need to know how the pelvis the foot the foramen magnum all contribute to bipedalism and remember if you can't see it in the picture and they ask for a visible reason don't give one that you can't see the next thing we spoke about was the position of the foramen magnum and remember it is more forward or more backward we spoke about the size of the cranium and that is linked to how much brain capacity you have the bigger the capranium the more brain you have the smarter you are we spoke about the canines getting smaller over time and that's because we cooked food and we chewed less we also spoke about the prognathus jaw which is the very large protruding jawbone that reduces over time remember you either have a prognathus jaw or you don't we spoke about the palate shape changing over time again that's linked to diet and the fact that we don't need large canines anymore we spoke about the cranial ridge or the sagittal crest which was that bone that sits on the top of your cranium again you either have it or it is reduced and in humans we don't have it at all because we don't need it anymore and last but not least the brow ridge the bone that sits just above your eye it is uh pretty much completely absent in humans or very very reduced in humans whereas it's much much larger in our ancestors and that's what you're going to look for look look for a brow ridge reducing over time now if you like this video don't forget to give it a thumbs up and make sure you're subscribed because i post new videos every tuesday and thursday and i will see you all again soon bye [Music]  hi everybody and welcome back to miss anglais biology class i am miss angler in today's video we are going to be looking at an introduction to human evolution where we're going to focus on the similarities and differences that we see between us and other primates i'm also going to walk you through how you can use this information to best explain yourself in an exam or a test because often in this particular topic we learn a lot of facts but we're not so sure how they're going to ask the question and what to expect now if you are new here don't forget to give this video a thumbs up and make sure you are subscribed with your notifications turned on because i post new content every tuesday and thursday and if you are on the trick and you're thinking about improving your mark and getting a distinction at the end of the year you might want to join my membership in the membership you have live lessons with me you get access to my study guide for free member only videos and so much more now before we get into this it's really important that we know how to navigate the family tree and also to understand what we're actually talking about when we use the word primate or hominid and where do we fit are we a monkey are we an ape and so i'm going to quickly break that down for you and one of the skills you need for the exams is being able to navigate through a phylogenetic tree or a cladogram like the one that we see in front of us here now essentially what you see here as the heading suggests is a primate tree of life in other words you can see us sitting at the end over here with all of our cousins now it's important to also note that this has been constructed this particular one has been constructed in such a way that it is showing how distant they are from us in other words the individuals that are closest to our left over here are more similar to us than perhaps the lima over here which is the furthest away from us now it's important to know that humans are not monkeys we are not gorillas um we are not gibbons or any of these other monkeys that you can see here on the slide instead we are what we call apes and apes are this final category at the very end over here and we're grouped together with orangutans gorillas chimpanzees bonobo chimps and there's us humans at the very end so that's the particular category that we're going to talk about now something i want to highlight to you is how to actually navigate your way through diagrams like this in exams and in tests so what you're actually looking for here is how related each individual is and we can actually calculate that by how many common ancestors they share so this is a cladogram it's a version of a phylogenetic tree there are some slight differences this one doesn't have any time on it phylogenetic trees generally have time scales on them but what you do have which is similar is you have these points where there seems to be like a break off point in other words an organism breaks off to the left here while the main line continues forwards or straight or up and those little breaks every time there is a break this little intersection creates something called a common ancestor now common ancestors are really important because they show us how related we are to one another and the more ancestors you share the more closely related you are and to give this a perfect example of something that they may ask you in an exam is they may say are humans more closely related to orangutans or to gorillas let's say for example now the only way to actually physically say this correctly is not to say well because of the diagram the gorilla is closer therefore you know they must be closer to us a relation it's not about closeness in the diagram what it is about is how many of these little intersections do we share with that organism so if we count how many humans share with orangutans then what we're looking for is how many we have before they split off so between humans and orangutans we share one two three four five six so we've got six with orangutans on gorillas on the other hand we share one two three four five six seven so the moment they deviate and they diverge that's where we need to stop counting so because we have seven ancestors shared with gorillas we're technically closer in relation to them than we are two orangutans now going into the next important piece of information that you need to be able to work with along with what we just saw now with the cladogram or the phylogenetic tree you may be asked to interpret you may also be asked to explain or even provide a table maybe of the similarities that we share with other apes and i'm just going to run through the top six things that we share with apes and the list is actually quite long it can actually continue but these are the main six that we share first of all the most important thing that we share with other apes is opposable thumbs and the picture alongside really highlights um two of the key things that we can do with our thumbs we have a great grip with our thumb which means we can use our thumbs to hold on to things but we also have precision now um this precision grip makes it really easy to use tools which again is  something that separates us from other primates and for that matter from other apes as well now the second thing that we have in common is we have no external tails and so all chimpanzees all gorillas if you think about orangutans they don't have tails and neither do we but if you compare us to monkeys monkeys have tails things like lemurs with vervet monkeys they all have tails so we don't have tails therefore that is something we have in common we have bare fingertips which means we don't have any claws we have binocular vision which means our eyes are placed in the front of our heads and we don't have any blind spot in the center of our vision because our eyes are close enough together in other words they're not too far on either side of our heads the fifth thing that we have is colour vision and this might surprise you but not all animals have color vision or the depth of color vision that we have and we can see pretty much all of the spectrums of colored light or visible light and the last thing is that the males are larger than females we call this and some textbooks call this sexually dimorphic as well it basically means that there is a male and a female sex and the males are often larger now um in terms of how they can ask this they don't really ask more than maybe three similarities but what is important that you must pay attention to is often they're going to ask you these similarities that we might have and then perhaps why they might be useful so for example if we think about why is it useful to have opposable thumbs well it's useful because you can grip things you can hold things you can make tools the next thing they may ask you is why is it useful to have binocular vision well your eyes are in the front of your head you can see danger you can see predators or you're able to hunt better and likewise with colour vision it improves our ability to differentiate between things that are maybe poisonous or uh be able to see warning signs and warning colors and animals so you may be asked to give a similarity and then substantiate your answer like give a reason as to why it is a useful thing to have next we need to go into the skeletal differences and first of all we're going to focus on the skull there is a lot of differences in the skulls that we need to point out and that you need to know the good news is that in terms of how many you should know if you need to like write them down as a list you probably really only need to know about three differences because often they ask you to tabulate the differences um the reason why perhaps you should also spend some time familiarizing yourself with any of these differences is often what they ask you is they'll say something like according to the picture in the text or in the exam what is the difference between skull a and skull b and then you have to give the differences that you can visually see so you need to have at least three differences that you can remember off by heart when looking at a picture or if asked for a list now we're going to start off with the most common and the most well-known difference between us and primates and that is going to be the location of the foramen magnum which we can see in the picture alongside here now the foramen magnum is the largest nerve hole or opening in the body and it is where the spinal cord leaves the cranium the skull and goes down the full length of your vertical column now what you will notice is that the human foramen magnum is positioned more forward and that's really important to use those words you shouldn't use more central um or in the center that's a no no no no so we are not going to use those words we are going to use it's more forward and for apes we're going to say it's more backward then in terms of the other differences we're going to take a look at this other diagram on the left hand side here and there are quite a number of differences and i'm going to start off with some of the easier ones the first is going to have to be the jaw and you will notice a difference between the two in size and what we call this very pronounced draw is a prognathus jaw now again there is some terminology that you must use and then also you must avoid when you talk about the size of the jaw or the fact that it's like big and bulky like this first photo we say that's a prague nathan's jaw when you talk about the human jaw you need to say that it is non-prognathus you cannot use the words less prognathus or decreasing prognathism you need to say prognathus or non-prognathus the next skeletal difference i want to highlight to you is a feature on the front of our face which is this over here the brow bone now in eighths you will notice that the brow bone is really really really really pronounced it's also known as the brow ridge but in humans you'll know it's greatly reduced you see it's barely visible on this picture the next thing that's really different in our skeletons is going to be the size of our cranium now the cranium in both of these pictures is vastly different in sizes humans have a large cranium whereas our cousins have a much smaller cranium and that's because  the size of our brains getting much bigger the next difference i want to highlight to you is going to have to be the canine teeth so these teeth over here and what's really interesting is the canines are really large in primates in other primates but if you'll notice in humans they're quite reduced and quite small and almost not noticeable another important feature in terms of skull differences is going to have to be a little area on the back of the skull and i'm just going to move some of these labels so you can see it better and you'll notice it almost looks like the skull has a ridge to it and i just want to highlight it it's this area over here you'll notice that we're sort of missing it over on our own and that structure is known as the sagittal crest now the sagittal crest did have a purpose in our ancestors and also in our cousins and i'm going to touch on that when i go through hominid evolution and phases of hominid evolution in the next video but we're actually missing it and the main reason why we're missing this little extra like piece of bone this little it almost looks like a fin is because essentially our chewing muscles in our cheeks have gotten smaller because we cook our food and so we don't need this extra piece to our skull to attach the muscle to now just briefly going back to the first point i made about the foramen magnum the foramen magnum is probably the most important indicator and skull difference for when it comes to an organism being able to walk on two legs which is a really important difference because humans walk on two legs all the time whereas chimpanzees and gorillas orangutans other primates they don't they might spend some time on two legs but they don't spend the majority of their time now the word associated with the foramen magnum and being able to walk on two legs is called bipedalism and this is one of the most important developments in our evolution that we must uh note and be aware of when we do this topic especially with this foramen magnum and in the next two skeletal differences and what they look like and how they assist bipedalism now as i mentioned the foramen magnum is the most important thing for bipedalism but we also need to look at the structural differences between the pelvis and the feet of other primates versus humans because it also tells us a story about whether or not these organisms could walk on two legs or not i'm going to start off with the feet and if you have a look here we have a gorilla and a human and one of the most classic classic things that you should look for in these diagrams is what we call a divergent toe now you will notice that the gorilla has a very large divergent toe there's a big space in between the big toe and the next toe in humans you will notice it isn't there there is no space so our toes are not divergent you can also typically say they're convergent they come together another important difference in our feet if you compare gorillas to humans and again this all supports bipedalism because remember that's the goal these skeletal differences must support the idea of bipedalism is the size of the heel bone now the heel bone in humans is much larger and that's because we spend so much time on two feet we need to put all our body weight into this bone and so the bone needs to be bigger and stronger in gorillas it's smaller because they spend very little time on their two feet then we move on to the pelvis now again the pelvis plays a really important role in bipedalism and you need to be able to tell the difference between any kind of diagram that you're given you need to be able to identify which one is the chimpanzee or which one is the ape and which one is the human now when we look at these two there are some key things i want you to notice first of all i want you to notice that the chimpanzee pelvis is reasonably longer if you notice compared to our own and you'll also notice that it is very narrow humans on the other hand we have a shorter pelvis but we have a much wider or broader pelvis so when you're explaining this in the exam or a test i suggest that you go for a description like this you want to go for a long narrow pelvis for describing chimpanzees or other apes when you're describing humans you want to say short and you want to say wide now again they're going to ask you why the questions always turn back to why is it long and narrow why is it short and wide well it's short and wide in humans because we are bipedal and we need to carry our body weight upright and so the shape of our pelvis supports that better and it allows us to have a center of gravity right in the middle of our body whereas chimpanzees have long narrow pelvises because they spend more time on all fours their body weight leans more in their chest so on the top of their body they're heavier on their top and so their bones need to be longer because they spend more time parallel to the ground and so that's why you need to be able to say the structure and then give a reason for the structure now as always i like to finish off my lessons with the terminology recap  please use these words for flash cards mind mapping your ideas out it makes it really quick and easy to do revision now first of all we spoke about primates remember primates are all of our cousins including monkeys and gorillas and so it's a very wide family tree however if you start to focus in specifically on us and our most close relatives we would use the word hominid and i'm going to go into more detail in our own specific hominid evolution in the next video and how we went from australopithecus to homo sapien we then looked at some key features and some of them are easier to remember than others but one of the most important similarities is the opposable thumbs that we share with primates and the binocular vision that we share with them then we went into the differences now the differences again are really important to know specifically one of the most important is the foramen magnum which is the location of where the spinal cord goes into the brain or vice versa with the spinal cord leaves the brain and that location is linked to bipedalism now bipedalism is the most important evolutionary change that's happened in humans and so whenever you are talking about well why is the pelvis the shape why is the foot this shape it all slowly but surely comes back to being able to walk on two feet our hands are free we can make tools um and there's so much that you could like speak about on that that i'm going to touch on in the next video we also spoke about the prognathus jaw um humans don't have a prognathus jaw we've got quite a a a small jaw and so when we say what it is we say non-prognathus whereas other privates have a prognathis jaw we then spoke about the differences in the cranium size so we have a very large cranium with no sagittal crests whereas primates have a small cranium and many of them have a sagittal crest on the top the last important difference is the canines the canines are really large in other primates whereas they're reduced in humans and that comes down to the whole thing about cooking our food and eating cooked food and no longer raw you see you need bigger canines because when you eat raw food you have to tear it and it takes more effort whereas humans cook our food so there's less effort involved and also we don't use our teeth anymore for territory or for fighting or anymore so we don't need very large teeth now if you like this video don't forget to give it a thumbs up and make sure you are subscribed i post every tuesday and thursday so also make sure notifications are turned on and i will see you all again soon bye  hi everybody and welcome back to miss anglais biology class i am miss angler in today's video we are going to be looking at an introduction to human evolution where we're going to focus on the similarities and differences that we see between us and other primates i'm also going to walk you through how you can use this information to best explain yourself in an exam or a test because often in this particular topic we learn a lot of facts but we're not so sure how they're going to ask the question and what to expect now if you are new here don't forget to give this video a thumbs up and make sure you are subscribed with your notifications turned on because i post new content every tuesday and thursday and if you are on the trick and you're thinking about improving your mark and getting a distinction at the end of the year you might want to join my membership in the membership you have live lessons with me you get access to my study guide for free member only videos and so much more now before we get into this it's really important that we know how to navigate the family tree and also to understand what we're actually talking about when we use the word primate or hominid and where do we fit are we a monkey are we an ape and so i'm going to quickly break that down for you and one of the skills you need for the exams is being able to navigate through a phylogenetic tree or a cladogram like the one that we see in front of us here now essentially what you see here as the heading suggests is a primate tree of life in other words you can see us sitting at the end over here with all of our cousins now it's important to also note that this has been constructed this particular one has been constructed in such a way that it is showing how distant they are from us in other words the individuals that are closest to our left over here are more similar to us than perhaps the lima over here which is the furthest away from us now it's important to know that humans are not monkeys we are not gorillas um we are not gibbons or any of these other monkeys that you can see here on the slide instead we are what we call apes and apes are this final category at the very end over here and we're grouped together with orangutans gorillas chimpanzees bonobo chimps and there's us humans at the very end so that's the particular category that we're going to talk about now something i want to highlight to you is how to actually navigate your way through diagrams like this in exams and in tests so what you're actually looking for here is how related each individual is and we can actually calculate that by how many common ancestors they share so this is a cladogram it's a version of a phylogenetic tree there are some slight differences this one doesn't have any time on it phylogenetic trees generally have time scales on them but what you do have which is similar is you have these points where there seems to be like a break off point in other words an organism breaks off to the left here while the main line continues forwards or straight or up and those little breaks every time there is a break this little intersection creates something called a common ancestor now common ancestors are really important because they show us how related we are to one another and the more ancestors you share the more closely related you are and to give this a perfect example of something that they may ask you in an exam is they may say are humans more closely related to orangutans or to gorillas let's say for example now the only way to actually physically say this correctly is not to say well because of the diagram the gorilla is closer therefore you know they must be closer to us a relation it's not about closeness in the diagram what it is about is how many of these little intersections do we share with that organism so if we count how many humans share with orangutans then what we're looking for is how many we have before they split off so between humans and orangutans we share one two three four five six so we've got six with orangutans on gorillas on the other hand we share one two three four five six seven so the moment they deviate and they diverge that's where we need to stop counting so because we have seven ancestors shared with gorillas we're technically closer in relation to them than we are two orangutans now going into the next important piece of information that you need to be able to work with along with what we just saw now with the cladogram or the phylogenetic tree you may be asked to interpret you may also be asked to explain or even provide a table maybe of the similarities that we share with other apes and i'm just going to run through the top six things that we share with apes and the list is actually quite long it can actually continue but these are the main six that we share first of all the most important thing that we share with other apes is opposable thumbs and the picture alongside really highlights um two of the key things that we can do with our thumbs we have a great grip with our thumb which means we can use our thumbs to hold on to things but we also have precision now um this precision grip makes it really easy to use tools which again is  something that separates us from other primates and for that matter from other apes as well now the second thing that we have in common is we have no external tails and so all chimpanzees all gorillas if you think about orangutans they don't have tails and neither do we but if you compare us to monkeys monkeys have tails things like lemurs with vervet monkeys they all have tails so we don't have tails therefore that is something we have in common we have bare fingertips which means we don't have any claws we have binocular vision which means our eyes are placed in the front of our heads and we don't have any blind spot in the center of our vision because our eyes are close enough together in other words they're not too far on either side of our heads the fifth thing that we have is colour vision and this might surprise you but not all animals have color vision or the depth of color vision that we have and we can see pretty much all of the spectrums of colored light or visible light and the last thing is that the males are larger than females we call this and some textbooks call this sexually dimorphic as well it basically means that there is a male and a female sex and the males are often larger now um in terms of how they can ask this they don't really ask more than maybe three similarities but what is important that you must pay attention to is often they're going to ask you these similarities that we might have and then perhaps why they might be useful so for example if we think about why is it useful to have opposable thumbs well it's useful because you can grip things you can hold things you can make tools the next thing they may ask you is why is it useful to have binocular vision well your eyes are in the front of your head you can see danger you can see predators or you're able to hunt better and likewise with colour vision it improves our ability to differentiate between things that are maybe poisonous or uh be able to see warning signs and warning colors and animals so you may be asked to give a similarity and then substantiate your answer like give a reason as to why it is a useful thing to have next we need to go into the skeletal differences and first of all we're going to focus on the skull there is a lot of differences in the skulls that we need to point out and that you need to know the good news is that in terms of how many you should know if you need to like write them down as a list you probably really only need to know about three differences because often they ask you to tabulate the differences um the reason why perhaps you should also spend some time familiarizing yourself with any of these differences is often what they ask you is they'll say something like according to the picture in the text or in the exam what is the difference between skull a and skull b and then you have to give the differences that you can visually see so you need to have at least three differences that you can remember off by heart when looking at a picture or if asked for a list now we're going to start off with the most common and the most well-known difference between us and primates and that is going to be the location of the foramen magnum which we can see in the picture alongside here now the foramen magnum is the largest nerve hole or opening in the body and it is where the spinal cord leaves the cranium the skull and goes down the full length of your vertical column now what you will notice is that the human foramen magnum is positioned more forward and that's really important to use those words you shouldn't use more central um or in the center that's a no no no no so we are not going to use those words we are going to use it's more forward and for apes we're going to say it's more backward then in terms of the other differences we're going to take a look at this other diagram on the left hand side here and there are quite a number of differences and i'm going to start off with some of the easier ones the first is going to have to be the jaw and you will notice a difference between the two in size and what we call this very pronounced draw is a prognathus jaw now again there is some terminology that you must use and then also you must avoid when you talk about the size of the jaw or the fact that it's like big and bulky like this first photo we say that's a prague nathan's jaw when you talk about the human jaw you need to say that it is non-prognathus you cannot use the words less prognathus or decreasing prognathism you need to say prognathus or non-prognathus the next skeletal difference i want to highlight to you is a feature on the front of our face which is this over here the brow bone now in eighths you will notice that the brow bone is really really really really pronounced it's also known as the brow ridge but in humans you'll know it's greatly reduced you see it's barely visible on this picture the next thing that's really different in our skeletons is going to be the size of our cranium now the cranium in both of these pictures is vastly different in sizes humans have a large cranium whereas our cousins have a much smaller cranium and that's because  the size of our brains getting much bigger the next difference i want to highlight to you is going to have to be the canine teeth so these teeth over here and what's really interesting is the canines are really large in primates in other primates but if you'll notice in humans they're quite reduced and quite small and almost not noticeable another important feature in terms of skull differences is going to have to be a little area on the back of the skull and i'm just going to move some of these labels so you can see it better and you'll notice it almost looks like the skull has a ridge to it and i just want to highlight it it's this area over here you'll notice that we're sort of missing it over on our own and that structure is known as the sagittal crest now the sagittal crest did have a purpose in our ancestors and also in our cousins and i'm going to touch on that when i go through hominid evolution and phases of hominid evolution in the next video but we're actually missing it and the main reason why we're missing this little extra like piece of bone this little it almost looks like a fin is because essentially our chewing muscles in our cheeks have gotten smaller because we cook our food and so we don't need this extra piece to our skull to attach the muscle to now just briefly going back to the first point i made about the foramen magnum the foramen magnum is probably the most important indicator and skull difference for when it comes to an organism being able to walk on two legs which is a really important difference because humans walk on two legs all the time whereas chimpanzees and gorillas orangutans other primates they don't they might spend some time on two legs but they don't spend the majority of their time now the word associated with the foramen magnum and being able to walk on two legs is called bipedalism and this is one of the most important developments in our evolution that we must uh note and be aware of when we do this topic especially with this foramen magnum and in the next two skeletal differences and what they look like and how they assist bipedalism now as i mentioned the foramen magnum is the most important thing for bipedalism but we also need to look at the structural differences between the pelvis and the feet of other primates versus humans because it also tells us a story about whether or not these organisms could walk on two legs or not i'm going to start off with the feet and if you have a look here we have a gorilla and a human and one of the most classic classic things that you should look for in these diagrams is what we call a divergent toe now you will notice that the gorilla has a very large divergent toe there's a big space in between the big toe and the next toe in humans you will notice it isn't there there is no space so our toes are not divergent you can also typically say they're convergent they come together another important difference in our feet if you compare gorillas to humans and again this all supports bipedalism because remember that's the goal these skeletal differences must support the idea of bipedalism is the size of the heel bone now the heel bone in humans is much larger and that's because we spend so much time on two feet we need to put all our body weight into this bone and so the bone needs to be bigger and stronger in gorillas it's smaller because they spend very little time on their two feet then we move on to the pelvis now again the pelvis plays a really important role in bipedalism and you need to be able to tell the difference between any kind of diagram that you're given you need to be able to identify which one is the chimpanzee or which one is the ape and which one is the human now when we look at these two there are some key things i want you to notice first of all i want you to notice that the chimpanzee pelvis is reasonably longer if you notice compared to our own and you'll also notice that it is very narrow humans on the other hand we have a shorter pelvis but we have a much wider or broader pelvis so when you're explaining this in the exam or a test i suggest that you go for a description like this you want to go for a long narrow pelvis for describing chimpanzees or other apes when you're describing humans you want to say short and you want to say wide now again they're going to ask you why the questions always turn back to why is it long and narrow why is it short and wide well it's short and wide in humans because we are bipedal and we need to carry our body weight upright and so the shape of our pelvis supports that better and it allows us to have a center of gravity right in the middle of our body whereas chimpanzees have long narrow pelvises because they spend more time on all fours their body weight leans more in their chest so on the top of their body they're heavier on their top and so their bones need to be longer because they spend more time parallel to the ground and so that's why you need to be able to say the structure and then give a reason for the structure now as always i like to finish off my lessons with the terminology recap  please use these words for flash cards mind mapping your ideas out it makes it really quick and easy to do revision now first of all we spoke about primates remember primates are all of our cousins including monkeys and gorillas and so it's a very wide family tree however if you start to focus in specifically on us and our most close relatives we would use the word hominid and i'm going to go into more detail in our own specific hominid evolution in the next video and how we went from australopithecus to homo sapien we then looked at some key features and some of them are easier to remember than others but one of the most important similarities is the opposable thumbs that we share with primates and the binocular vision that we share with them then we went into the differences now the differences again are really important to know specifically one of the most important is the foramen magnum which is the location of where the spinal cord goes into the brain or vice versa with the spinal cord leaves the brain and that location is linked to bipedalism now bipedalism is the most important evolutionary change that's happened in humans and so whenever you are talking about well why is the pelvis the shape why is the foot this shape it all slowly but surely comes back to being able to walk on two feet our hands are free we can make tools um and there's so much that you could like speak about on that that i'm going to touch on in the next video we also spoke about the prognathus jaw um humans don't have a prognathus jaw we've got quite a a a small jaw and so when we say what it is we say non-prognathus whereas other privates have a prognathis jaw we then spoke about the differences in the cranium size so we have a very large cranium with no sagittal crests whereas primates have a small cranium and many of them have a sagittal crest on the top the last important difference is the canines the canines are really large in other primates whereas they're reduced in humans and that comes down to the whole thing about cooking our food and eating cooked food and no longer raw you see you need bigger canines because when you eat raw food you have to tear it and it takes more effort whereas humans cook our food so there's less effort involved and also we don't use our teeth anymore for territory or for fighting or anymore so we don't need very large teeth now if you like this video don't forget to give it a thumbs up and make sure you are subscribed i post every tuesday and thursday so also make sure notifications are turned on and i will see you all again soon bye  hi everybody and welcome back to miss angus biology class i am miss angler and in today's video we are going to be looking at lamarchism we're going to look at his theory how we use his principles to explain evolution and to go through the basics and make sure that you'd be able to apply lamarcusm to any kind of exam question that you may see now if you are new here don't forget to give this video a thumbs up subscribe and make sure your notifications are turned on because i post new content every tuesday and thursday if you are in matrick and finals are coming up very soon and you need that little bit of extra help you should think about joining my membership there are so many perks including members only videos live lessons with me and of course a free copy of my study guide is included for those of you who join the rescue me option so before we start off looking at lamarck's principles we just need to put his theory into context so that you know exactly how he came to these conclusions and why is it that we don't actually consider lamarcism a reasonable way to explain evolution today a couple of things we need to keep in mind is lamarck would have formulated his theory long before genetics which means that in the terms of explaining how things are inherited genetics hadn't been discovered yet so lamarck would have been before mandel remember mandel we learned earlier in the year about genetics he explained how we inherited things lamarck had no information on that just yet so we couldn't necessarily base our explanation of evolution on that genetics just yet another thing as well that wasn't very well identified just yet was dna now obviously dna is a component of genetics but likewise there wasn't very much clear data at that point about what dna was and what it's made out of and how it moves from individual to individual all we knew at this point during lamarck is that somehow offspring looks similar to their parents and obviously some kind of information has been passed from one organism to the next but we didn't know what those things were just yet and so lamarck looked for a way to describe and explain how it would be possible that organisms came to look and behave the way they do today why do they have the structures that they have and how is it possible to then give that onto their offspring in order to truly understand lamarcusm we need to look at his hypothesis which was the inheritance of acquired characteristics now this particular hypothesis has two main fundamental principles that govern it and support this theory and he used these to explain how it works you'll notice one of them when i show it to you is a repeat of the theory's name i don't want you to be too worried about that i'm going to explain why that is the case soon what i want to do first though is just quickly break down the name of his theory so that we are on the same page and we understand where he's coming from with this so when we speak about inheritance let's not forget that this is the way in which organisms uh pass on characteristics from parents to offspring no lamarck didn't know about genes and genetics just yet but he knew that there was like something that was being passed on then we look at the word acquired now acquired means you gained this trait or characteristic throughout the course of your life and you are going to then pass it on and you'll see now why that doesn't quite work when it comes to genetics that you can't just inherit things that you've acquired through the course of your life now when we explain this particular hypothesis we use the first principle of use and disuse which is a fairly simple and straightforward idea and it's broken down into a couple of parts but essentially what it is is if we have a look here it is the organism that is responding to the environment which in other words means the organism has decided itself that it wants to respond to whatever has changed it's gotten hotter it's gotten colder their food is underwater maybe maybe they need to fly now and they are responding to it and when they responded to these changes in the environment they're doing it actively which means that they're actively changing their body to survive now we know that this is not the case just because you want to be able to fly it doesn't mean you can fly doesn't mean you can grow wings or feathers and so for this theory to work an organism would need to actively be able to change their physiology or change their anatomy and as we know this is not the case you cannot will something to happen you don't want to be you can't will to be taller and then you're going to grow taller um and to sort of explain this even further he used the idea of using something more or less and he suggested that if you were to use a structure more it would become bigger or stronger if you were to use a structure less it becomes smaller and weaker until eventually it actually disappears and for some instances this is quite confusing because to some people this makes sense it makes common sense if i use my legs more they will become more muscular yes that is the case they will become more muscular but you can't necessarily grow  longer legs you can't grow another leg so it's important to know that when we speak about these users and how you change your structures you are just changing them also within yourself which brings me to the second main component of this theory which as i mentioned to you at the beginning of this that the inheritance of acquired characteristics comes up twice and the reason for that is we are speaking about the phenotypic changes or the physical changes that we see in organisms now as we've already learned in our previous topic the physical changes that happen to you in genetics it cannot affect your your your genotype so for example if you dye your hair pink that is a phenotypic change that phenotypic change cannot be translated to your dna and then passed on to your children in other words you dyed your hair pink that is now part of your dna and it's passed on to your children so they have pink hair that is not the case okay but however to lamarck he theorized and used this as a principle and said well actually the way in which organisms change during the course of their life there's physical phenotypic changes they are acquired by the parent and then during their lifetime they've acquired it and they're going to pass it on to their offspring now as i just mentioned that's just not the case we can't change our physical characteristics and then our dna follows those two things are not linked to one another in that way specifically your genes can make your phenotype and they do but your phenotype cannot influence your genotype so things you physically change to yourself in your course of your lifetime can't affect the way you look or behave now to apply this idea one of the most common examples is the one i have alongside here which is lamarck's giraffes and basically it was a way in which landmark was trying to explain how giraffes got longer necks now originally if we start with the first generation giraffes began with a short nick which is actually true that is an evolutionary thing they did have shortened x and over time their necks actually did get longer as time went along and he would have described it in uh in his own two theories and principles he would have said something along the lines of the food was out of reach for our giraffes so what did they do they actively responded to the environment by stretching their necks making them longer so that they could reach the leaves they then passed on that physical phenotypic change to their offspring and their offspring were born with longer necks and then the cycle repeated the next generation was slightly longer necks did it again they responded to the environment they actively adapted to their new environment making their neck longer that physical change was then passed on to their offspring resulting in the third generation with an even longer neck and so on and so forth so when you are explaining this in an exam you need to use these two principles use and disuse and the inheritance of acquired characteristics those two to explain any kind of example you may meet now what i would like to do now is just a very quick application example so if you ever come across this in an exam you know exactly what to do because they don't always give you the giraffe example they can give you any animal and they'll ask something like using lamarck's theory or how would have lamarck explained um the way in which lizards lost their legs and became snakes so when you're formulating your answer you must mention both of his principles under his theory the first one of course being the law of use and of disuse now in this instance when we're speaking about our lizard we are going to focus more on the disuse side right because remember you're going to say something like lizards used their legs less and because they you use their legs less their legs disappeared and they no longer have any legs right they become weaker over time they didn't need them the second thing that you need to do in your answer remember is to speak about the inheritance of a quiet characteristics and when we speak about that remember we're talking about passing it on to our offspring so what we do in the next part of our answer is we need to speak about how that change which is the no leg or if you don't want to go straight to no leg you could also say smaller legs or weaker legs and you're going to say that that characteristic is then passed on to offspring now it is important of course to mention in your explanation that all of this is occurring because your lizard is responding to the environment and it might be because there's more food there's less food maybe there's a temperature change but essentially um you need to say that this has happened because the lizard is responding to the environment and they are actively and that's another important word we want to put in there we want to say that they are actively changing themselves it means that they know that they're changing themselves and they're doing it on purpose and that's basically it and you can apply to any kind of animal or person or behavior take the principles as i mentioned in the previous section of the video and just apply it to the topic  that you're working with and make sure that you speak about that specific example that they're asking about if they want giraffes they'll ask for giraffes so if they want a general explanation just give them a general one you don't have to use any kind of specific structure or animal only work with what they give you now as always i like to do a terminology recap at the end of every session and this particular one's gonna be very quick because we didn't do a lot of terms we rather just did some application and some theories and so remember when we are speaking about lamarcusm we are speaking about the uh theory in which organisms have um actively changed their bodies and have passed that on to their offspring we also then looked at the fact that lamarck speaks about a phenotype change in other words it's a phenotypic thing that's happening remember that doesn't actually work because you can't change your physical characteristics and then change your dna and then we looked at these two principles which was the use and disuse principle use it more becomes stronger use it less becomes weaker and then eventually disappears and then the acquired characteristics those are the ones that are accumulated during the course of the organism's life and then passed on to their offspring now if you like this video don't forget to give it a thumbs up and make sure you are subscribed with the notifications on and i'll see you all again soon bye  hi everybody and welcome back today we're going to be looking at the theory of natural selection and how it falls into place when we look at the evolution of a species it's important to note at the beginning of this video that we are going to be dealing with natural selection which is a mechanism of evolution i'm not going to be covering speciation in this video there will be a separate video for how a new species arises keeping that in mind i want you to remember the following thing throughout the whole video that natural selection is a mechanism of evolution it's like a tool that you need in order for a species to evolve it doesn't always end in a new species arising and so that's why i've had to separate natural selection and speciation from one another and that's why you should know that they are not the same thing and that natural selection does not always result in a new species arising now the idea of evolution and natural selection has been changing for some time and one of the first few people to identify natural selection but didn't really have a word for it at the time was lamarck now jean-baptiste lemak was a naturalist and he suggested a mechanism that allowed a species to change over time and ultimately make it best suited for its environment now currently a la marxism is not a credited source anymore and it is no longer used to describe natural selection and evolution but we need to learn it because it ultimately tells us what doesn't produce natural selection and why this doesn't work and essentially with lamarckism he had two laws or principles that explained his idea of evolution and very famously he is known for his example of using giraffes and that's why very often you'll see a lot of giraffe imagery and i'm going to use the giraffe as an example very soon to explain it but essentially if we sum that up in this picture the jean baptiste lamarck would have said that long-necked giraffes evolved as generations of giraffes stretch their necks to reach higher leaves now if you know anything about genetics you know that this proposes a bit of an issue because if you change yourself physically it doesn't necessarily change your genetics in other words if you dye your hair pink your children are not going to have pink hair and that's not how it works but unfortunately lamar didn't have any genetics knowledge at the time because that field of study in biology hadn't been developed yet instead he had two other principles now the first law is centered around the idea of use and disuse and essentially what lamarck means by that is he believed that if you use a structure more it will become more developed and if you use it less it will become less developed now i know why this might seem like it makes sense for example your muscles if you use your muscles more they grow and they develop and if you use them less they essentially atrophy which means that they get weaker but your muscles aren't disappearing and i think that's the important idea what he was actually saying was it's not that you use it more it gets better what he's really meaning is that if you were to want to see further if you strained your eyes to allow you to see further off into the distance he literally means that your eyes are going to get stronger you're going to change the physical properties of the lens in your eye all of the nerve cells in your eye and it's almost like you can change that you can make it better and that's just not possible genetically that's not possible you can't change your genes and your eyesight through wanting to see further away and using your eyes more and that's like saying if you don't use your eyes you're going to lose the ability to see which is not the case at all you could be blindfolded for 10 years and then when you take the blindfold off you can still have your sight you won't have lost it in any way the second law that's linked to lamarckism is the law of acquired characteristics and what that means is the characteristics like the using the structure more and making it better or using it less that is a quiet meaning it's gained during the course of the animal's life and then it is inherited or it's passed on to the offspring now yet again we know that this is not true because in genetics you cannot change your genotype during the course of your life and then pass that on to your offspring and you certainly can't choose to do that either we know now with modern science that the only way that you can pass on any changes to your offspring is in your gametes and it's often a result due to mutation so it's not necessarily something that you have you have chosen to change about yourself and so now how do these two laws apply to his giraffes and i'm going to use his giraffes as an example so essentially what he would have said is giraffes would have started off with a short neck which they actually did however what he suggested was they used their necks more and more by stretching them and over generations they got longer because they needed to reach the food higher and higher and so what you had is a use of the neck being used more and stretching it and going further  and further and when that slightly shorter neck giraffe stretched its neck it somehow changed itself and that was then passed on to the next generation and then the next generation and each generation getting a slightly longer neck than the one before until we end up with the giraffes that we have today with the longest necks now if you know anything about biology adding structures to an animal or any organism is very difficult when it's being added out of nothingness that's like adding an extra vertebra bone in your spinal column and it's it's just not possible you can't think about something and then grow it and so lamarcusm is not a credited source of evolution instead the most basic and the most commonly used form is darwinism which is what we're going to go into next now darwinism and the idea of what we also call gradualism is a way in which to explain how evolution occurs and it is linked to also the rate at which evolution occurs and so darwinism was proposed by charles darwin and he spent a huge proportion of his life and studying animals and figuring out exactly how they actually change over time and what's causing them to change and why are they changing and so his idea is slightly different when it comes to the giraffes instead darwin would have said that you had long neck giraffes and they are born randomly in other words some giraffes have shorter necks and some giraffes have a little bit longer necks and we can see that in humans as an example some humans are shorter than others some are taller but they're all still human so there's variation and those who have the longer necks are more successful because they can eat better they don't have to compete as much so they produce more offspring and any organisms that are competing with each other often die and don't survive and so if you have a longer neck you have a competitive advantage and so i'm going to go step by step through natural selection in the future part of this video but let me just break down a little bit more of this so sitting around darwin's central idea is there are four main ideas that guide his explanation number one more offspring opera juice than needed and we see this in many examples of animals often animals produce more than two offspring which is more than is necessary as you only need one to replace each of the parents now within any species you always need natural variation and we see this amongst ourselves in humans but we see that amongst animals as well basically we're looking for differences in height and color and texture and these little variations between individuals allow for evolution to take hold just think of humans we have a variety of hair colors skin colors heights body weights eye colors blood groups all these variations improve our chances of evolving and surviving the third important thing is that the environment creates the selective pressure now what that means is and what darwin meant is basically nature selects using selective pressures like predation competition parasitism diseases essentially there is competition between individuals within a population to survive so they're either competing for mates they're competing for shelter or food and you might have a variation in your genes which makes you stronger and fitter and that means that you are likely to resist the selective pressure and that you can be successful and that you can live and lastly and this is a very important one and this was missing essentially from lamarcism is that the traits are inheritable now lamarck said that you acquire these inherited characteristics but what he meant there is you've gained something in the course of your life in your genetics and you're giving it to your children but darwin is saying rather that these little variations little changes must happen in the dna they can't happen in your physical body they can't happen in your hair color they can't happen if you for example lose an arm it doesn't mean that your children will therefore lose their arm or be born without an arm darwin is saying that in order for there to be a change it must happen in the dna it must be genetic and it must affect the genotype and that is then passed on to future offspring so now what we're going to do is we're going to look at the step-by-step process of natural selection using an example so now let's look at this dear mouse example and let's pretend that we find this population of mice and they have a dark fur color and currently they live in a forest and the traits that they have allow them to survive and so in this in this particular area they're probably a dark brown color they suit the surroundings maybe the darker areas of the forest and right now they have variation in their colors and some might be a little darker than others maybe some a little bit lighter but they're still all a brown color now let's say for example some of these uh dark brown mice they get relocated maybe they're washed onto an island far away from where they used to live in the forest and now they're on a new environment with new challenges but also new advantages and unfortunately um this particular island that they now  find themselves on has a lighter sand and that means that in terms of their coloring that they have they really stand out and they're going to be very easy to spot to predators because they don't have anything camouflaging themselves now what you have is the development of what we call favorable traits and so at this point when they were in the forest they had a favorable trait that allowed them to survive but now we've got these dark-colored mice on a light-colored sand and so now this trait isn't so favorable anymore it's becoming an unfavorable thing to have because it could lead to their possible death now as i mentioned before with darwin's ideas and his theories he said that there is going to be genetic variation which means that within this dark brown population of mice there are going to be some who are lighter than others and we can see that in humans as well we can see it in dogs and cats their all their fur colors are not perfectly identical to one another and that can be the case with our mice now the light-colored mice are not necessarily a new species and this is really important this is not the production of a new species rather it is simply a favorable trait that's been selected for so let's say our mice are now reproducing with one another and the gene mutation occurs now that gene mutation results in this very very light fu and i want you to know that gene mutations are often random and they are not caused by the mouse wanting to be a different color and so now what happens is we end up with more and more and more tan colored mice in other words this lighter color and now we have all this genetic variation we've got dark-colored mice and light-colored mice and essentially and they all exist in the same place competing for the same resources and safety as well and i think we can see where this is going but essentially if you are the lighter fur colored mice you are more likely to survive because you camouflage better but the darker individuals don't so now this links into these selective pressures which we mentioned about darwinism earlier on and so because the sand was a lighter color the tan colored mice had a better chance of survival because they were able to blend into the sand this means most of the dark masks died now an example like we see here is of predation and predators often determine a lot of evolution because those who have the unfavorable trait do not survive and they can't reproduce so let's explain this a little bit clearly essentially what you have is competition amongst organisms some have favorable traits like being a tan light color and some have unfavorable traits who have a dark color the ones that are tan and lighter are more likely to survive and reproduce whereas those with the darker color are less likely to survive and therefore less likely to produ reproduce now remember reproduction is very important for carrying on genetics now i'm going to pause there i want to remind you that even if we removed a lot of these dark brown mice we haven't lost the dark brown gene completely because if you know anything about genetics you know about recessive and dominant traits and sometimes a trait can be hidden and it can be masked by a dominant trait and so it's not necessarily true that we have lost every single dark brown mouse it could just be that all the tan mice are carrying the gene for the darker hair color but we don't actually see it it's not being expressed so now we see this playing out in our next picture here where