Lecture 17_ Discovering the origins of mankind.pdf

Lecture 17: Discovering the origins of mankind Is there a missing link? ● The idea of missing link – an old idea, goes back to Darwin’s life time ● Soon came to mean something in human evolution ● There was the idea that there is something like a gap or hole that does not connect human to other spec...

Lecture 17: Discovering the origins of mankind Is there a missing link? ● The idea of missing link – an old idea, goes back to Darwin’s life time ● Soon came to mean something in human evolution ● There was the idea that there is something like a gap or hole that does not connect human to other species ● Easy to believe concept because we look so different from others ● A false appearance. The idea of missing link is a misconception. There is no such thing. Darwin and his predecessors had NO fossil evidence of human origins ● Darwin’s day there was none. There was no human fossil has ever been discovered. Or anything resembling human. ● The human species seems quite different from others - almost isolated… is/was there a missing link? ● There seemed to be no traces of anything connecting modern humans with pre-human ancestors. ● No fossils of any apes were known, partly because of the rareness of these fossils, but also because the places where people were digging up fossils were mostly in Britain and Northern Europe, and apes never lived there ● Darwin and his contemporaries like Huxley put forward the argument that human beings had evolved from other species without fossil evidence because they didn’t have any at that time, it was based on anatomy and physiology and so forth Ernst Haeckel’s Paleontological Tree of Vertebrates (1879) ● Ernst Haeckel was one of Darwin's biggest supporters in Germany, he was a very fine artist ● Looking at the tree on the right, you can see fishes, reptiles, mammals, and particularly the age of man in bigger bolder letters. This tree kind of gives the impression that all the other things like marsupials are somehow more primitive, they are stages along the way to becoming a human being. (humans are the pinnacle, most successful) ● Darwin’s theory however, everything that is alive have the same ancestor, 4.5 billion years ago ▪ No increasing complexity & no direction implied in Darwin’s theory unlike in this theory ● The tree on the left makes that point because right at the pinnacle of it is man, human beings of evolution (most successful) ▪ Old fashioned view and does not follow Darwin evolution ● This is not accepted at all in a biological or Darwinian sense. The way to read a tree is that every tip of a lineage that reaches the present timeline has been evolving just as long. There should be lines of marsupials right up there (on the right tree) because there are marsupials alive today, and they have just as much life history as the other mammals that are up there Humans have many vestigial structures: ● Darwin made powerful uses of vestigial structures in human bodies to argue that we have these structures from earlier ancestors ● Appendix can be surgically removed, and there is no statistical evidence that people are any worse off without it ● Fingernails and toenails bear an obvious relation to the scratchy things on the tips of the appendages of other land animals ● Our pelvis, skeleton has gone from a horizontal one to pushed upwards (for walking upright), which leads to lower back problems, women have painful birth processes because of the compromise between walking upright and squeezing a big baby head through the birth canal ● Darwin pointed out that reason we have the unpleasant arrangement of our air tube and food tube right next to each other with the constant danger of choking is a by-product of the first animals that came onto land after the insects, whereby the fish’s swim bladder was gradually converted into lungs. It’s not a structure that is completely optimised The fossil trail begins (1856 & 1886) ● 1856 a skull cap found in Neander valley (Tal or Thal) of Germany. ● In 1886, Neanderthal remains found a few years before the publication of Origin of Species ▪ Another species of human (bigger and stronger) *extinct ● Obviously, something very human like, but they could also see that it was not the same as modern humans from these small fragments, the size of the skull was not right. What was it? Was it some sort of gigantic super ape or a diseased human with a terrible deformity? ● Neanderthal much shorter than other humans, have big noses to warm the air they breathe. Rather than migrate, they stay within the same valleys all year long. Neanderthals are stronger and more heavily built than other humans, and their thick bones and barrel chest help them to deal with a very tough lifestyle. Because Neanderthals were much bigger, they did not have pelvis problems, apparently giving birth was no big deal ● We don’t really know if Neanderthals looked a lot like modern humans, if we would be able to easily tell them apart from modern humans ● We know from their DNA that some Neanderthals had red hair, which is possibly the source of people who have red hair today, it was claimed that there was some interbreeding between homo sapiens and Neanderthals ● It used to be believed that the Neanderthal was our ancestor, that was eventually dispelled. Neanderthals are in essence our cousins; we have the same ancestors as the Neanderthals. Neanderthals also evolved in Africa, and they left Africa and colonised a good chunk of the globe, which is where their fossils are now found ● Stereotypical view of all Neanderthals being stupid cavemen is wrong. Neanderthals were intelligent creatures like us, we do not know if they had language, but not only do they walk on 2 legs like us, they made clothes, artifacts, weapons, possibly jewellery, and they had fire like us. ● Documentary hinted that they were killed off by the last ice age, this is not likely true because they probably had lived through a couple of ice ages before that, and the relationship between the arrival of Homo sapiens on the scene, followed by the rapid extinction of competing species seems to be too obvious to ignore. We probably did them in, maybe we killed them, maybe we were better at exploiting the environment than they were and ate all their food, maybe they caught some of our diseases, we don’t know. When Neanderthals vanished, they left us alone, which is why we are the only human species left. ● Relationship between Neanderthals and modern humans = cousins 1891 Java Man ● 1887 Eugene Dubois went to Indonesia. ● In 1891 he discovered a skull cap and femur which he named Homo erectus called “Java Man” ● Inspired to find fossils for origins of human beings. ● He was persuaded to look to Asia. ● Darwin thought it must be from Africa since our closest relatives are there. ● But there is Orang Utan in Asia. Some people thought Asia must be the place. ● 2 very interesting pieces to find. The skull, ape like, big brain. The leg shows that it walked upright but it is not human. ● Smaller than humans ● Similar to humans, extinct shortly after another species of human came out. Piltdown Man (1912) FAKE ● Fragments of a skull and jawbone, supposedly collected in 1912 from a gravel pit at Piltdown, East Sussex, England ● Darwin predicted that walking upright evolved first, big brains probably evolved after that. But the Piltdown Man caused a problem with that ● Piltdown Man looked like a very modern human skull with a very ape like jawbone. This made it look like maybe big brains came first, because this has a fully modern human brain size ● This was a hoax, a fake, we never figured out who was responsible for it. It really is a modern human skull with a baboon jaw put on it. It was always disputed, but it was only in the 1950s that it was completely uncovered as a hoax ● Europeans did not like the idea that humans had evolved in Africa, they wanted modern, big brained intelligent humans to have evolved in Europe ● Those racist Europeans. Peking man 1923-1937 (Beijing) ● 500,000 and 300,000 years old ● A type of Homo erectus ● Upright walking creature, can tell from where the hole is at the base of the skull and the angle at which the spine enters the skull that its spine is upright, not horizontal ● Peking Man being the same species as Java Man showed that this creature was widely distributed, made the Asia case a little stronger. These 2 ancient fossil forms, 2 of the earliest ever found were from Asia (except for the confusing Piltdown Man) Taung, South Africa 1924 ● “Taung Child” ▪ Not human species ● Australopithecus africanus = “southern ape of Africa” ● 3.03 and 2.04 million years old ▪ Much much older before human beings appeared ● Human beings have a flat skull angle. This one like other apes have a bit of protruding skull but not very much. Ape like skull. ● Probably also walked upright ● Human-like but different species from humans, protruding snout Homo habilis 1960 ● Olduvai Gorge, Tanzania, East Africa ● Homo habilis = "handy-man “ ● 1.75 million years old ● Skull and reconstruction show a very ape like creature, not particularly human ● But was something which walked around upright (human-like) “Lucy” 1973 ● Australopithecus afarensis ● Found in Ethiopia in 1973- 3.2 million years old (Africa) ● Most famous. ● Young female, very small ▪ Animal that walked up right, human like pelvis ▪ Ape like creature / chimpanzee like ▪ Walk upright like we do but have a small brain like chimpanzee ● The argument of which came first was settled, the legs (walking upright) came long before big brains ● Humans and chimpanzees ancestors and 6 million years ago ● Lucy and chimpanzees share: Elongated skull with small brain case, face and jaws that jut out from the brain case, shoulder blades and joints that are suited for climbing trees, long arms and hands with curved fingers ● Lucy and humans share: Spine connection beneath the skull to keep the head steady, robust and broad basin-shaped pelvis to support the upper body and hold it upright, angled thigh bones that place the weight directly over strong knee joints, compact and arched feet that support the full body weight with each step Laetoli, Tanzania, 1976-1978 ● A track of fossilised footprints 3.6 million years old ● They were made by three individual Australopithecus afarensis (Lucy) ▪ Human and chimpanzee ancestors (we don’t come from chimpanzee) ● Made by the same species as lucy – australopithecines ● There was a volcanic eruption, there was soft volcanic ash on ground fossil footprints preserved when the ashes turned to stone ● Gives us evidence of how they walked (basically identically to how we walked) ● Same species as Lucy, brain about the size of a chimpanzee, no more intelligent as a chimpanzee. Basically, chimpanzees on 2 legs ● Why do they walk on 2 legs? ▪ Keep heads above water to find food as they travel (water takes the weight off their bodies so they can stay upright much longer) Why did hominids start walking on two legs? ● Question has never really been satisfactorily answered ● Bipedalism is not that rare, has happened over and over again but why these early ape creatures? ● To see farther over new savannahs ● Freeing up their hands to do stuff ● Hunting theory: we can run more efficiently, longer distances on 2 legs vs 4 (although apparently 4 legs are faster at short bursts). Walking on 2 legs allows the animal to see a longer distance, gives a higher viewpoint, easier to spot predators or ● ● ● ● prey. But all of these seem to be kind of retrospective explanations. You have to be able to imagine an animal going about its daily business in a way that it would require or benefit it to walk upright when its ancestors have not done so before, there has to be a reason for this change. Tree’s theory: Based on a recent study, orangutans spend a considerable portion of their time moving on their hind legs in the trees. This is quite new, it is a possibility that their upright stance may have not been something that happened after they came down to the ground, but something that began while they were still on the trees. It is gradual, and it makes sense that an animal that is already comfortable moving on 2 legs is more likely to adapt to living on the ground. Reason they started living on the ground is believed to be widespread loss of forests in Africa where these creatures lived. Instead of swinging from branches, there were lots of grasslands and savannahs. There simply wasn’t the old tree forest environment that had supported their ancestors Aquatic ape theory: theory put out by someone who is an outsider, got bashed by experts. The theory is that a substantial part of our evolutionary past was conducted in the water, there would have been a phase of the evolution of these creatures in which they would have done a lot of wading (this is supposed to explain the loss of body hair, because wading with almost naked skin is better than being covered in hair which will slow you down). If you have a baby in the first 3 or 6 months if you drop them in water they will not drown, they automatically hold their breath, and are not even distressed. The aquatic ape theory is not doing very well because the required aquatic environment has not been found. From the video about the aquatic ape theory: about 6 million years ago, the climate of the Earth became very erratic, the great African forests began to die back, and there is some evidence that slow movements in the Earth’s crust caused areas of Africa to flood. A new habitat had appeared for the apes. As the forests diminished, the apes had to travel further from one tree to the next, which involved crossing open spaces covered with grass, or even water, and to do that they travelled upright on 2 feet. Ancestors had to wade and keep head above water in order to find food. Apes are primarily adapted for live in the trees, which is why it is tiring for them to stand on 2 feet. But when they wade, the water supports their bodies, and takes some of the strain off their leg muscles, so they can stay upright for much longer. Maybe a life at the water’s edge encouraged anatomical change, and at about this time, the hip bones of these early ape men altered, and our ancestors adopted an upright existence This theory is not doing very well. If apes were really living in watery place, where is this place? (Video of Chimpanzee walking on 2 legs in water in Africa) The evolution of big brains ● Video on Geladas ● Group size is related to brain size, the larger the group the larger the brain size (correlation) ▪ Human brain size are similar to our social group of 150 ▪ Helps to keep track of everyone else ● Likely that the need to communicate detailed social information between many individuals that lead to evolution of language in humans ● Although monkeys living in the treetops have rich, varied lives, it is the monkeys that came down to the ground and formed large groups that have the most complex and communicative societies of all (like in Ethiopia) ● Big brains are probably to keep track of everyone else if you are living in a large group of other clever apes Homo floresiensis & Denisovans ● Latest hominin discoveries ● 2010 Denisovans ● 2003 floresiensis (nicknamed the Hobbits as they were very short) o 4000 years ago, they died out o Modern human reached these islands 4000 years ago (killed them directly or indirectly) o When a super predator come, these things die off / go extinct (human does this many times) Victorian times no fossil evidence of human evolution ● Today is different. ● No fossil evidence for human evolution in Victorian times, but today we have a vast fossil record of the hominids ● The old idea of us ascending from Neanderthals has been replaced by both modern humans and Neanderthals originating from a common ancestor ● Apparently, the Homo erectus (Java Man and Peking Man) was species that survived quite a long time until comparatively recently there, at one time there were at least 3 species of things like us running around ● We have a very complex family group history ● Human beings seem so isolated and separate and different from everything else in the natural world because all of the others that were so obviously intermediates between us and other things like other apes are all gone ● If there were 20 other species of upright walking apes in the world, walking upright would not be considered a big deal. Because all the others died out and their existence was unknown, walking upright for a long time was the pinnacle of nature’s perfection, because only we walk upright (except for birds and a few other things). But now we know that there were lots and lots of other creatures which were very similar to us ● The ancestors, earlier species made objects, they made spheres and sharpened stones to cut open animals. For thousands and thousands of years, they made identical objects, their material culture did not evolve. Human beings do not ever make things the same. This is how archaeology works, you can tell how old, what century an object is from by its shape, the way it was made, the material etc. We can date any object that is made by humans, it is very specific to a particular time. We do not know why our ancestors went from being creatures that always made identical shaped hand axes to making different objects. The objects that we have made ever since then has ● ● ● ● always changed, we cannot make stuff identically anymore. This is associated with our humanness Homo floresiensis (2003): One of the most recent finds, fossils found on the island of Flores in Southeast Asia, dwarf sized little ape creatures that were quite small in stature, they have been called hobbits. Nobody has really figured out where they go yet, this diagram has left it to the imagination. Denisovans, 2010 Tree has Neanderthals and us splitting off, then recombining because there was interbreeding between homo sapiens and Neanderthals. ▪ Modern humans interbreed with neanderthals Out of Africa ● Darwin was right! Humans evolved in Africa ▪ He wrote in descent of man, vol 1, page 199 ● We know now from the fossil record that humans did evolve in Africa ● Human ‘races’ what are they? Do they exists? ▪ It is not a biological thing, but is individual differences between human varieties ▪ Races exists but there is a lot of intermixing nowadays ▪ Complex, not a simple yes or no issue ▪ What are races? Races is a synonym for varieties. There is a lot of dispute whether races even exist, some people say that it is a social construct. But we all know that there are differences between human beings, everything about us varies – our height, skin colour, texture of your hair, colour of your eyes etc ● There used to be more than one species of human, e.g. the Neanderthals ● Darwin used the theory of sexual selection to explain why different human races existed, he did not think that the earlier theory that humans were adapted to their local environment was correct. He tried to argue that humans have domesticated ourselves and made our own races through sexual choice, by mating based on their standard of beauty. This is nonsense and is not accepted ● The theory that Darwin did not want to accept turns out to be more correct, which is that different varieties of humans are in essence adapted to their local environment. But it depends on how long they have been there, which is the problem that Darwin had. Some human groups have not been where they are for very long, so it would be superficial to say that they are adapted to that particular place because they are not, they were from somewhere else ● There are some remarkable cases of change, for example there are people from extremely high altitudes in the Andes who have larger lungs, larger hearts, and more RBCs than the rest of us. It is a subtle change but is still a difference. People native to tropics tend to be smaller in stature, due to the body surface area to body size ratio, smaller people can dissipate heat more efficiently. Those from the tropics perspire less (true in South America, Asia, and in Africa) because sweating is ineffective in the tropics where the humidity is very high ● Skin colour: since all our ancestors originally came out of Africa, we all basically had the same skin colour, probably quite dark. It has happened independently more than once that the dark pigmentation has been lost. The melanin is to protect your skin from UV radiation, but for someone in high latitudes with very little sunlight, if the sun blocking is so effective, you do not have enough vitamin D. Mutations or variations for lighter skin colour probably happened very rapidly. North Asians and North Europeans have very pale skin, but it is not the same colour. This is because both lightening events are a result of independent mutations. ● It was once disputed whether all the races were commonly descended or simply different species descended from different ancestors. Darwin, along with many others argued that all human beings are descended from the same ancestors, races are simply local variations of one species. It is hard to believe they disputed this because it was known even then during Darwin’s days that all human races interbreed with each other, and have had successful offspring ● Question during Darwin time: Were all the races commonly descended? Or were human races simply different species? Darwin argued that all human beings descend from common ancestor. Out of Africa map. (Early human migrations) ● At least 3 species left Africa. ▪ 1. Homo sapiens ▪ 2. Neanderthals ▪ 3. Early Hominids ● Early hominids like homo erectus came first, and went to all the places that are green ● Red arrows shows where modern humans went and what time, e.g. we reached Australia 50,000 years ago ● Native Americans came from Asia, probably during one of the last ice ages when the sea level was much lower. They filled up the entire continent within a very short time, driving lots of species extinct like humans have always done when we reached somewhere new ● Madagascar was one of the last places to be reached. People who colonised Madagascar were Malays ● We (homo sapiens) are a very successful species, very good generalists, we can live in lots of different habitats, we can make warm clothing to survive where it is cold, we can use fire and make fire (we took a while to figure out how to make fire, we had fire for a long time before we learnt to make it) ● In modern times the most isolated group of people in the world were the Tasmanians, they had been isolated after the last ice age when the glaciers melted and sea level rose, and Tasmania became cut off from Australia. They also had the simplest technology; they were the only people ever recorded in modern history who could not make fire. They carried fire around with them with special sticks that sort of glowed like a cigarette, which they carried from one campsite to another. But if the fire ran out, they did not know how to make it, and had to get fire from another group. Everywhere else in the world humans knew how to make fire. Isolation there meant that a lot of things were lost, they lost the ability to make boats, bows and arrows, the objects that they made were vastly fewer in number and type ● Any objects made by humans can be dated. Very specific to a particular time. What is wrong with this picture? ● This is a stereotypical evolution picture, supposedly implies progress towards us, and that everything was inevitably leading towards us. The fossil record does not show that, the fossil record shows that there was a large variety of bipedal apes that have existed. Now there is only one left, and this may be having just as much to do with accident as with anything else ▪ Evolution has no direction and progress unlike this picture ● Fossils show that it simply went from 4 legged things to 2, there’s no halfway, no intermediate hunching way of walking on 2 legs ● This picture is wrong because it implies inevitability, direction. There is no direction, goal in evolution, simply descent with modification ● Linage of the great apes, the orangutans spilt off first, they are the most different of the surviving great apes. Then the gorilla broke off before our ancestors spilt from the chimpanzees. The chimpanzees have spilt into 2 species in more recent times ● Our closest living relative is the chimpanzee, we share about 95% of DNA with chimpanzees ● Idea that walking on 2 legs happened very quickly seems plausible because we see actual apes alive today that do walk on their hind legs. Maybe it is a slightly mutated pelvis that makes it easier for them to walk upright? ● For these other animals, they live in forests, there is no pressure that is going to drive them towards being bipedal, they have been getting along just fine as they are in their current environment ● Humans are a type of ape. 5 types of great apes A common question: “Are we still evolving?” YES ● Difficult question, because it is based on some misunderstandings ▪ Implying a direction, but no there is no direction ● One sense of the word evolve: how did the giraffe get its long neck? It evolved from a giraffe ancestor with a short neck, giraffes’ necks gradually got longer ● Another sense of evolve: some big change happened. When asking are we still evolving, it implies ‘is some big change happening’. But a big change only happens over many thousands of years. You cannot ask if we are still evolving meaningfully. Is something that takes thousands of years happening right now? We do not know. ● It is meaningless to ask if anything is still evolving, because it implies big changes like are, we are growing wings or something like that, but it doesn't work that way. All that ever happens now is the same that has always happened – parents and offspring, parents and offspring, nothing more dramatic than that has ever happened in the history of life or at any greater speed then what we are experiencing in our lifetime. The process is very slow and gradual, and is invisible to the individual because our lifetime is so short (except things that have a very short life span, in those species we can see them evolving quickly) ● Things that changed recently in human species: ● 1) Skin colour: Ancestors initially white (because they had hair) but only after they lost their hair, they became dark pigmentation. // migrate then light skin evolved again to produce more vitamin D ▪ Light skin became more pale due to individual mutations ● 2) The ability to digest dairy products is one of the significant differences between Asians and non-Asians. In Europe, almost everyone can digest dairy products as an adult. This is something that is lost in other mammals, after they are weaned, they lose the ability to digest milk, because they will never need it again. Some people can digest dairy products all their lives, and these people are descended from populations which have traditionally kept animals for herding (cattle, goats and so forth). In Asians there is a huge proportion of people who cannot digest dairy products. This is a biological feature that has emerged very recently ● 3) Blue eyes are believed to have evolved recently, not sure why, they do not seem to have any particular advantage. Blue eyes are recessive, brown eyes are dominant ● 4) Wisdom teeth are left over from having larger jaws in the past, we know from the fossil records that our jaws have reduced in size, some people are born without wisdom teeth ● 5) Disease resistance in humans is one very obvious way we have changed over a reasonably short period of time. When the Europeans reached the Americas after Columbus, they infected them with nasty diseases and killed off a lot of people in the New World which had no natural immunity to the diseases. Why isn’t this happening ● ● ● ● anymore? Because they have evolved to adapt to these diseases. Over the next couple of hundred years, the inhabitants of the New World who were susceptible to diseases were killed off, the few that did survive had natural immunity, and their descendants are the ones who are still alive Diseases are so hard to eradicate because they evolve rapidly. A new flu is probably descended from an earlier flu, but it is not the same, it has evolved. People often use the word mutated, but the correct word to use is evolved. The disease is a population of little things, and they evolve and constantly change. There is no fast forward, no prediction in evolution. We will either keep having successful offspring, or not Evolution is the process of slow gradual change. What is evolution after all? 🡪 Variations that make a difference to surviving and that can be inherited…. [and natural selection mostly does] Why are there still chimpanzees? 🡪 adapt to their environment, to where they live. // question with misconception as evolution is not about progress, is adaptation We are just 2 different species from the same ancestor, adapted to different living conditions and environment. Chimpanzees adapt very well to their niche in the natural world (to fit where they live) 🡪 they even have their cultures HUGE misconception is that humans are the pinnacle and evolution is about progress