Lecture 14: The Descent of Man PDF

Lecture 14: The Descent of Man The variation of animals and plants under domestication (1868) ● The only part of Darwin’s ‘big book’ on the origin of species which was printed in his lifetime and corresponds to its first two intended chapters. ● The first part of the projected 3 parts of the big boo...

Lecture 14: The Descent of Man The variation of animals and plants under domestication (1868) ● The only part of Darwin’s ‘big book’ on the origin of species which was printed in his lifetime and corresponds to its first two intended chapters. ● The first part of the projected 3 parts of the big book. The other 2 was never published. ● His longest work / his longest booj ● Variations – a big part of his theory. Darwin’s theory worked because living things vary. They are not all identical copies. ● He made intense study on variations. ● One thing he studied – domesticated poultry (Artificial selection) o How we change animals and plant ● Victorians were obsessed with breeding animals o Gave Darwin a way in [DARWIN’S BOOK] The power of human selection ● Darwin talks about how human beings make animal breeds. o Power of human selection (from ubiquitous variations) o Can change the skeleton of the chicken o Made the Polish fowl 🡪 made by humans and cannot survive in nature (cannot be formed due to evolution as their eyes cannot be seen) ● Darwin spent a lot of time taking about pigeons o Being selected by human variations o Wild rock pigeons (common ones we see today) ● Human breeders were mostly working class people ● Traditional view is just that they all just existed or come from different place. ● Darwin used this to show that the same thing happens in nature. ● Breeders will choose and select which one to breed from. ● The point that Darwin was making by showing the skull of the bones was that farmers or breeders can only see the external appearance of the bird (i.e. the feathers, headdress) and choose which one to breed from and over a long time, they had breed one with an astonishing and almost blinding headdress, Polish Fowl. ● What humans were inadvertently doing was changing the skeletons of the birds as well. So, there was this bizarre dome on the front. ● Changing the shape of the brain, change the intelligence? Darwin asked phrenologist. Darwin found out Polish Fowl just as stupid as any other chicken. ● Darwin collected pigeons. Human beings “made this” by artificially selected the pigeons with a bigger head gear. No way this would survive naturally. Domestic pigeons ● Illustrated in Darwin’s book ● Gentlemen’s club putting their fancy breeds on display. There was competition between people about who could have the perfect breed. ● People who kept and were making these breeds, they believe that all these breeds were descended from wild ancestor. o Darwin’s book was controversial as people thought these pigeons exists all these time while. ● Darwin said there is no possible wild ancestor species in the world of these breeds. He argued all derived from the wild pigeon – the rock pigeon. o Selection explains adaption “provisional hypothesis of pangenesis” ● Means origins of our genes ● This book has a new theory. ● Provisional – speculative ● Pangenesis – pan means encompassing, and genesis means birth. ● He did not know how exactly inheritance works. No one did at that time. This was Darwin’s guess of how it works. He speculated that cells of the body give off little particles called Gemmules. o Gemmules – these recorded the information from the cell it came from. How characteristics are transformed from parent to offspring. This theory also allows characteristics gained during lifetime. o Idea is not new as people had this idea long time ago though Darwin believed this was new ● This theory very unpopular. Not widely accepted at all. ● E.g. His cousin, Francis Galton, conducted experiment on bunnies. He stuck needles into the rabbits and sucked out and transfused their blood. He took out blood from one bunny and put it into another one and would wait for them to have offspring. He took out blood from a black rabbit and put into a white rabbit and wait for the white bunny to have offspring to see if it has any black ones. But nothing was passed on so he said Darwin’s theory was wrong. Darwin was not convinced because he didn’t say that they (gemmules) were exactly in the blood. ● This idea is not new. Not an area where Darwin flies. ● This book is so long, probably less read of all Darwin’s book ● Almost ten years since origin of SPECIES, his theory is doing very well in scientific community. But he wants to keep reminding people the overview of his theory. Darwin, Variation ● Overview of his theory of evolution, o pp. 5-6., descent with modification as method of production of new species o “If then organic beings in a state of nature vary even in a slight degree…of which we have abundant geological evidence, or from any other cause; if, in the long course of ages, inheritable variations ever arise in any way advantageous to any being under its excessively complex and changing relations of life; … then the severe and often-recurrent struggle for existence will determine that those variations, however slight, which are favourable shall ● ● ● ● ● be preserved or selected, and those which are unfavourable shall be destroyed.” o pp. 10-11 “To exhume with one's own hands the bones of extinct and gigantic quadrupeds bring the whole question of the succession of species vividly before one's mind; and I had found in South America great pieces of tesselated armour exactly like, but on a magnificent scale, that covering the pigmy armadillo… Here then we see the prevalence, as if by descent, in time as in space, of the same types in the same areas… … New species come in gradually one by one. Ancient and extinct forms of life often show combined or intermediate characters, like the words of a dead language with respect to its several offshoots or living tongues. All these and other such facts seemed to me to point to descent with modification as the method of production of new groups of species.” 🡪 like how ancient spoked Latin and language like Spanish descended from Latin Critics would ask 🡪 What causes the variations? o Where do variations come from? Darwin couldn’t answer this. He doesn’t know the source of these variations. Darwin couldn’t answer this, like why is one pigeon slightly darker than the other? Darwin does not know the cause or source of variation. People would pick on this and say that since you cannot explain this, it must be God. They wanted a guided evolution. So, Darwin says: look at all these rocks that have broken down at the base of a cliff, lots of different sizes, shapes and variation. Darwin’s analogy of blocks of stone. o If a builder used these rocks to build a house, how did the rocks get to all those shapes, just nice to build a house? This is an analogy to his own theory: I have explained how species came about and why they are adapted to their environment, but I cannot explain how different variations arise in the first place. Just like the rocks at the base of the cliff, there were naturalistic explanations on why rocks have their unique shapes – weathering/chipping etc. We cannot explain the origin of different variations, but we can see the consequence of that fact. o There must be natural causes though I cant tell you 🡪 SUMMARY OF WHAT DARWIN SAID What Darwin is focusing on is the consequence of variation not what causes variation. 🡪 FOCUS OF HIS THEORY OF EVOLUTION o All offsprings vary [DARWIN’S SECOND BOOK] The Descent of Man (1871) ● Two volumes, selection in relation to sex ● Origin of species is not about human but about the general process of biological change over time. ● He was not shirking anything or holding back. But he did think it would add to the prejudices against his theory. ● Now, in 1871 when Huxley’s book on evolution (first book on evolution) and Lyell’s book on the ubiquity of man had been published. The theory of evolution in general have been accepted. So now I can talk about human evolution in particular book. ● But the book did not create any sensation as the battle is over. As people already published on this topic. Darwin kind of said the same thing. So, nobody was shocked. General remarks on Descent of man (1871) ● Descent is practically 2 books 🡪 selection in relation to sex ● Darwin explained sexual differences such as male antlers, spurs on roosters or the peacock’s tail as the result of differential success in males either competing against other males or being chosen by females and therefore leaving more offspring o FIRST TIME DARWIN USES THE WORD EVOLUTION AND NOT EVOLVED. ● Sexual difference part – differences between species ● The word 'evolution' occurs, for the first time in any of Darwin's works. ● "...as these two species [gorillas and chimpanzees] are now man's nearest allies, it is somewhat more probable that our early progenitors lived on the African continent than elsewhere." o Not new 🡪 people before Darwin knew that humans were close to gorillas and chimpanzees ● One book on human evolution. Another book on sexual selection ● He used the word evolution for this first time in his books. ● Made remarkable predictions – gorillas and chimpanzees therefore our ancestors from Africa. Very accurate prediction Three main kinds of anatomical features that indicate our (human) descent / evolve from other primates Evidence according to Darwin, man descended from earlier species or primates. (But humans are primates) EVIDENCE 1: Homologies (=similarities of same structures in different species) o Skeleton o Nerves, blood, entrails, brain… (layout) o Diseases spread between humans and other animals (disease on trees or fish hard to get, humans can catch disease from chimpanzees or gorillas) o Same ailments, monkey get drunk and smoke o Have sex and make babies the same way ● Patters and structures of the nerves etc… are the same across families. ● A lot of similarities. If a disease can pass from one to another, they must have very close structure. Show they have very similar and a lot in common. (same susceptibility) ● They must have very similar physiology to engage in same practices. ● Give birth in the same way. No radically different thing with human. ● “On any other view the similarity of pattern between the hand of a man or monkey, the foot of a horse, the flipper of a seal, the wing of a bat, &c, is utterly inexplicable.” o Nothing else can explain this EVIDENCE 2: Embryology (study of embryos) o Man start from egg like all other animal (descendants from eggs) o Grow tails 🡪 then later legs o Gill slits, growth of blood vessels o Hairy covering in 6th month, called lanugo (humans) o Showing the sort of common features that indicate common origin / common ancestry ● Embryos were similar in similar stages of development (indicate common origin) o And they were like NOTHING in the adult form o Like humans grow gills then later don’t have 🡪 grow into lungs ● Radically the new part of Darwin’s theory o Darwin has been studying this theory for years ● One is dog and another is human. ● At early stages of development of embryos, they resemble very closely. Then later, they diverge more. ● Why should the embryos go through the stages of other species to become_____? ● Darwin said is a kind of vestige of ancestry / leftover o Doesn’t matter as it doesn’t hurt 🡪 so it remained there coz of ancestry leftover ● Like tail that is on human embryo is a leftover from the ancestor EVIDENCE 3: Rudimentary (vestigial) organs o Muscles to: twitch skin like horses, move scalp (like how some humans can do that, but has no use anymore), move and direct the ears (similar to donkeys and mules) ▪ Many species, including humans, have muscle twitching / muscle spasm 🡪 though it is not useful anymore (but left because of ancestry leftover) o Darwin point (slight point on the ear) 🡪 ancestry leftover (our ancient ancestors must be like flying lemurs with pointy ears and like the fetus of an orangutan 🡪 orang in Darwin bk) o Third eyelid – ink spot in eye (protect eyes in other animals) 🡪 pink bump at order of the eye (no function, leftover from ancestors, cats currently have it) o Unerupted third molars (wisdom teeth) from shortened human jaw than human’s closest relative (many people now in the world are born without wisdom teeth now) o The shortened caecum in the intestines, is an adaptation to the change of diet from plant only diet to omnivore diet (humans eat and digest plants and meat) o Body hair 🡪 doesn’t give you warmth and doesn’t keep you cool anymore (no function) o Goosebumps (space under hair follicles) 🡪 used to fluff up hair but now humans don’t have ● Muscles under the skin. Same muscles present in other animals but human do not do anything with it. ● Muscles to move ear. We have muscles to do that, but we cannot point it any longer. ● Organs that doesn’t serve any functions for humans. So they are leftovers. ● The ‘Darwin’ point. According to Darwin, this point is a remnant of pointy ears. ● Picture of head of orang utan foetus with the point. ● Human ear is descended from a pointy ear that has flattened. ● A remnant of a third eyelid. ● Why do we have wisdom teeth? Vestigial structure that has not been lost. The human jaw has become smaller. We have very small jaw in the primate family. ● Shorten caecum in the intestines. We can digest both meat and plant. ● Everyone probably has the same number of hair but just smaller. Our hairs – rather useless. ● Quadrumana – old word for primate ● Darwin’s conclusion: Ascidians – sea squids. Most primitive animal in the ocean. In their larva stage, looks like tadpole. Have primitive version of spinal cord. The most likely earliest ancestor of vertebrates ● If a baby is born with a tail 🡪 called reversion (which is a former condition of our early progenitors) o Because go back to ancestors’ traits Sexual Selection ● ¾ of the 2 volumes book is on his theory of sexual selection. Not just human beings. o And he uses this to explain human race ● Darwin thought human race are not the result of adaptation to environment but due to natural selection o Darwin rejects the notion that humanity consists of more than one species in spite of geographical diversity (he knew that there was geographic diversity) o People used to believe that there was more than 1 species of humans (which Darwin rejected but was wrong) 🡪 easier for slavery justify where slaves are closer to animals (but by Darwin’s days, this view is on NO more than one human species was common, Darwin was not unique ) o HE WAS WRONG THAT 1) HUMAN RACE ARE NOT RESULT OF ADAPTATION; 2) HUMAN RACE DOES NOT CONSISTS OF MORE THAN ONE SPECIES (>1 species theory was popular in the past) ● Why do human races exist? o One theory – maybe they are adapted to the place o Blacks Africans are different species ▪ Darwin rejected all these. ● Unconventional way of explaining human races. ● Most people think dark skin in higher exposure to sun light etc… ● There are exceptions that Darwin is aware of. Human beings moved around a lot. ● His theory – races due to sexual selection. o In insects, fish, lizards, primate, and especially birds Sexual dimorphism 🡪 systematic difference in different sex (gender) of the same species Pigeons only mate with their own kind. Human have made the races by choosing what they like. Woman choosing what they like. Darwin think human being create their own breeds He spent most of his time discussing other animals. Male vs. male competition o Male of various species fight to get girls. o Explain why many males have weapons to fight other males. o Great difference between male and female species. o Males have become to be the shape they are because the girls like it. o The one with the best weapon get the girl so they survive. ▪ Sexual dimorphism ▪ Lizard Strepslceros Kudu, Damalis pygarga (nails for fighting for other girls) ▪ Beetle (fighting horns males but females don’t have) 🡪 to fight 🡪 corpris isidis, phanarus faungus, dipelleus cantorl, onthophagus rangifer ● Variations like bigger horns etc 🡪 can get females easier ▪ Honeybird (big showy feather to impress the female) o ● ● ● ● Argus pheasant – most famous example (from earlier point on sexual selection) ● Darwin wants to show that his theory can explain the most beautiful structure in birds ● The design of this feather is like a 3D object. (big tail, have structure that looks like eyes, circular structure) It could not have come about by itself. ● Darwin’s contemporaries find hard to accept that animals have a sense of beauty ● Darwin says females discriminate and choose which male o The most dazzling parts of the feathers are being selected by the females. So overtime, more males with dazzling feathers are chosen, and sexual selection then results in more males with dazzling birds o Not popular. o Because people think animals do not have a sense of beauty 🡪 resulted in critics & comics making fun ● Darwin said females carefully choose the males ● His conclusion: o Females are very choosy. Not just appearance but also songs o Darwin’s theory of sexual attention did not get much attention for many years. Only in recent decades its revived. o No ape has a tail, cartoons of Darwin making fun of him pop out Humans Come from apes – Darwin (chimpanzees, gorillas etc all descend from apes too) o A lot of people think Darwin said monkeys but no o o Humans descend from apes, not monkeys, seen by tree diagram drawn by Darwin showing the primates. 🡪 lemurs then apes ▪ Monkeys that can wrap their tail around trees are from South America 1868, drew tree diagram of primates separating into monkeys and apes [DARWIN’S THIRD BOOK] The expression of the emotions in man and animals (1872) ● Third and final book ● Start out as a chapter in descent of man but could not fit in and published as separate book. ● Darwin is targeting/attacking Charles Bell (man of science), Charles Bell claimed that man is provided with special muscles just for expressing emotions. ● Darwin showed instead that human emotions and their expression were present to some degree in other animals. o Human beings do not have any unique emotions / unique muscles for expressions to them ● the main human expressions are universal in all human races, additional evidence that all are descended from ‘a single parent-stock’. ● Because of the difficulties of observing the fleeting expression of emotions Darwin used photographs in addition to the usual woodcuts. ● Human beings do not have unique muscles. ● One of the first scientific books to use photography. Some say it is the first, not sure. Expression of emotions (1872) ● Shocking to Victorians. Not acceptable. To say something that is unique to human as not. ● The differences in mental functions between humans and other animals is one of degree, not difference of kind. ● Similarity in expressions of animals and humans o Black meercat 🡪 hair combed back and show teeth when want to scare o Dog body posture changes during expression o Cat are demonstrating emotions with body emotions o Darwin also showed human expressions with photographs (painting wasn’t enough and photographs had a 20 secs lag) 🡪 but Darwin found a good photographer // also captured Darwin and him trying to portray expressions himself 3 times 🡪 “what do you mean by insulting me? I really could not help it.. // also had a man who had numb nerve and was electrocuted ● Morality as a more refined development of other social animals o Morality was sacred in Victorian times so it was shocking ● Reciprocity and concern for the welfare of relatives had become accentuated in human beings and that is why we have this feature. ● The things we consider noble about human beings – heroism, sympathy, generosity/virtue are all derived from ancestors who had survived better by doing these things. They were accentuated in human beings and have those traits. ● Emotions come from a common source and not gained individually. Determined by questionnaire sent Darwin argued that there were three general principles of expression ● Serviceable actions become habitual in association with certain states of the mind and are performed whether or not of service in each particular case’. ● ‘antithesis. The habit of voluntarily performing opposite movements under opposite impulses has become firmly established in us by the practice of our whole lives. Hence, if certain actions have been regularly performed, in accordance with our first principle, under a certain frame of mind, there will be a strong and involuntary tendency to the performance of directly opposite actions, whether these are of any use, under the excitement of an opposite frame of mind.’ ● ‘the direct action of the nervous system’ ‘on the body, independently of the will and in part of habit’.