Lecture 19_ New theories of human evolution_ The cooking ape hypothesis.pdf

Lecture 19: New theories of human evolution: The cooking ape hypothesis Cooking ape theory ● Based on the work of a brilliant primatologist named Richard Wrangham ● Richard Wrangham studies chimpanzees and for 20 or 30 years, he had followed chimpanzees through the forest in Africa, and observed th...

Lecture 19: New theories of human evolution: The cooking ape hypothesis Cooking ape theory ● Based on the work of a brilliant primatologist named Richard Wrangham ● Richard Wrangham studies chimpanzees and for 20 or 30 years, he had followed chimpanzees through the forest in Africa, and observed them, in particular their diet. ● He tried out everything they ate, except for a couple of disgusting bodily secretion. ● He said that the first thing to say about chimp food, is that it is disgusting, it tastes terrible to human beings, awful! They taste very bitter and very dry and chewing on leaves is basically impossible. You cannot live on it. ▪ Human teeth cannot chew on it and it is disgusting ● In fact, he stayed with a tribe of pygmies who lived in the same forest as the chimpanzees. ● He asked them about the food in the forest and what the chimps ate. They told him that even in years of terrible starvation, when everyone is dying, they cannot live on chimp food even if they tried. ● This is interesting because chimpanzees are the closest animal to us, genetically and anatomically. ● If the chimpanzees are closest to us, what makes us special? How did we get this intelligence ● **He said calories on labels (processed) differ from its raw form 🡪 way of cooking affects the calories What makes human special? ● His take on this is to look at the diet of human. ● Is eating meat a mistake or are we naturally vegetarians? ▪ Not a biological mistake because we are omnivores. Goes back before humans existed. ▪ Our ancestors have ate one another ● Is eating living enzymes good for you? (digestion) ▪ Yes, good for health but doesn’t mean that you can swallow more to become more healthy ▪ No. It goes into your stomach and get destroyed by stomach acid. Meat-eating hypothesis for human traits ● Traditional theory – meat eating. Chauvinistic – suggest men the one hunting etc… men deserve the credit. ● It kind of suggested that man is responsible for human evolution because man went out hunting and get all the meat and brought it back and everyone start eating meat and somehow the australopithecines evolved into brilliant humans. It is kind of inadvertently suggested that man deserves all the credit for human evolution. ● Tempting theory, but don’t think it works. ● Meat-eating does give a lot more calories that eating plants. ● We know that they ate meat because there are scratch marks. From bones that are 2.6 million years old and onwards, there are cut marks from the stone tools that these creatures made on bones. So we know that they were cutting up animals. And if you are cutting up animals, some of the cuts go through and you scratch the bones underneath, or maybe you scratch off the meat left one the bones with the tool. We can get meat eating dated by that means. Meat eating goes way back, far beyond. ● After all, the chimps eat meat too, they are omnivores. Old theory – Only meat could explain why human beings become so intelligent ● Only meat can explain our big brains. ● But meat eating goes far back, before our big brains. ● What is the natural food of human? The closest thing we can do is observe what modern hunting society does. But they are not ancient people but modern. Cannot say they are exactly like ancient hunter gatherer. But they are the closest. Meat eating lead to homo (sapiens) 🡪 present day humans? ● So, the old theory was that only meat could explain how human beings get so intelligent; only meat could explain how we get this gigantic jelly field heads, swollen fat heads. ● Our brain is very unusual; they are extremely large. We are very different because of our brains. ● Meat was considered to be the cause of this. ● But meat eating goes way way back, way way back before all these changes took place. Walking came first. Small brain creatures walked around and eat meat and they stayed small brain for quite a while. ● What is the proper food for a particular animal? Fleas-suck blood. Giraffe-leaves. Dolphins-fish. But what is the natural, original food of humans? Fruits (so do chimps) and meat and other food. ● The closest thing we could go by, aside from archaeological evidence, is what modern hunter gatherers have done since they were being observed for the last 100-150 years, not many are left now. Many modern hunter gatherer societies have been observed. They were considered the ‘original’ people because they are still living as hunter gatherers. But it is a mistake, they are not ancient people, they are modern people. They are people alive in the present and they just have many years of history behind their society as we do. So, one must be careful in equating them as the same that modern hunter gatherers are exactly the way ancient hunter gatherers were 100000 years ago. But they are the closet thing we got to observe and how ancient humans lived and ate. His theory – cooking is unique to human. The cooking hypothesis that cooking has real effect (as it was dismissed in the past) *controversial as he is not a palaeontologist (studies history of earth through fossil record) 🡪 he studies chimpanzees (1) Biologically adapted to eating cooked food ● We cook food because we can. ▪ Cooking food is one of the very few things that is universal about human beings. Human societies around the world are so diverse that they are very few things that you can say that it is universal. ▪ Eg: hunter gatherers ▪ What about sushi? ● Even religions and belief in supernatural beings are not universal. There are societies in the world that have no gods. But in Darwin’s day, this (having gods) is thought to be universal; every tribes and race in the world believe in god, so there must surely be a god. This is what people believed during those days. But this was not true. ● One thing that is very crystal clear is that cooking is universal. All human groups ever encountered in the history of the world and those exist today all eat cooked food. ● But what about eskimos who eat raw seals and sushi? Sashimi? ● All those cases that you can think are delicacies. ● Sushi is primarily cooked rice. Most of the food matter is cooked with a bit of raw fish. But nobody lives on sashimi. They live on cooked food. Eskimos who supposedly live on raw seals only eat raw meat in special circumstances when they are out hunting in the ice. When they are out hunting on the ice, they could not start the fire so they would eat raw meat during the day. All the travellers who saw this always reported this. But Eskimos do not live on raw meat. They lived on a diet of cooked food. The men went home at night and the womenfolk would have a cooked meal for them. If Eskimo hunters went home to the igloo and if there was not a hot meal waiting for him, he would have kicked her (wife) out of the snow and tell her to get lost and throw her things out. It is essential that after a long day hunting in the snow, they would come home to cooked food. Their meal is primarily cooked. (2) No known cases of long-term survival on raw food in the wild ● Wrangham went out to look for instances in which it had been recorded that human beings have ever lived a long period of raw food. ● One of the most famous case is that Alexander Selkirk, who is the origin of the story of Robinson Crusoe, a man who had been stranded on an island for many years by himself and made a house. He cooked his food. ▪ “got fire by rubbing two sticks of Piemento Wood together upon his knee” 🡪 Juan Fernandez Island 400 miles West of Chile 1704 - 1709 ● There were many cases on people who were lost in the sea on their boat for a long period of time and all they could get were seagulls and fishes and they could live for a month on raw food. But again, as long as you have plenty of freshwater to drink, you can live for a month without eating. ● The longest recorded case he could find was a woman in South America who was held captive by an Indian Tribe, the Yamamomo. She escaped and lived in the forest for 6 months. She could make no fire but she stumbled on an abandoned banana plantation, and she survived for 6 months. Bananas are man-made, they are domesticated. They are not ancient food. They are gigantic bananas, not the small ancient bananas. ▪ A case of survival on modern domesticated food doesn’t really show anything (3) Long term Raw foodist live only in cities (we need cooked food) ● Movement that claim eating cooked food is bad and unnatural. The natural thing is raw food. E.g. fruits. ▪ These people claim health benefits of raw food. ▪ They think cooking destroys the nutrients. ▪ Book: Nature’s first law: The raw food diet (arlin, dini, wolfe) 🡪 nature, raw, natural ▪ Most of them have vegetarian diet. ● ● ● ● ● ▪ These people claim it’s a better diet This would go against Wrengham theory. (cooking is unique to human) Hard to do studies of effect of raw food diet on human beings because they do not live in a laboratory --🡪 We do not know for certain if they cheat. These people only exist in western cities, with 24 hour supermarkets loaded with domesticated food products that doesn’t exist in ancient times. Modern supermarkets have all kinds of food from all places all the time. Unlike ancient times. Why eating raw food make you lose weight? ▪ Due to not enough energy (not healthy diet) ▪ Raw food is less digestible than cooked food. Body must do more work to break down that food. Shocking: The raw food diet, have not only drastic weight loss, and 50 percent of woman studied cease to menstruate (amenorrhea, sterile) which is evidence of malnutrition and starvation. ▪ People who do attempt to eat uncooked food suffer these effects. ▪ Happened in Nazi War camps also ▪ Even if these people are eating the ‘most amazing’ food that had existed since the history of the world in abundance that never existed, they can have as much as they want, they eat huge quantities of food, but they are always hungry and they are suffering effects of starvation. (4) Human guts are small ● For a primate of our size, we have really 2 small guts. That means there is less digestive pathway to give a good battering of what you eat. ▪ So we eat cooked food as we cannot digest raw food diet ● Gorilla has giant guts. We don’t have that big guts that’s why we can’t eat leaves, we can’t digest them. ▪ The chimps can eat and digest leaves. We are not equipped to eat the same kind of food as chimpanzees. ▪ Giant guts are needed to digest their raw food diet ● Our teeth / molars are incredibly small. We have the smallest teeth of any mammals in terms of body size. ▪ Having small teeth means we cannot do what other primates do. They can chew piles of leaves because they have massive grinning teeth. ▪ Adapted to soft diet, not (raw) meat ● Human are biologically adapted to eat cooked food. Fire ● Fire has been controlled for > 200, 000 ya ● The big problem for Wrangham’s theory is the origins of fire. How far back do we have evidence of the use of fire by these early hominids ▪ Evidence is not entirely clear so the map shows ● Undoubted hearths, convincing sites, contested sits on when did fire get controlled ● Neanderthals also have fire. But as we go back to these earlier creatures, such as the homo heidelbergensis and homo erectus, the evidence is very patchy. So, if Wrangham is right, somewhere in here, the cooking business should have started, in other words, becoming adapted to eating of cooked diet should have evolved. Because it is at that time that the ribcage of the skeleton gets small, the barrel chest vanished of these early ape things like Lucy and australopithecines have a huge belly for stewing all the nasty stuff they ate, and it got narrow and the jaw went in and the teeth got smaller. ● Wrangham argues that the only way to explain those features of our anatomy is that those creatures were eating cooked food, which is drastically, vastly softer and easier to chew than raw food. Our jaw muscles are much weaker even per size of let’s say chimpanzees and other primates. There is a change in our chewing muscles, they are weaker. The bite power of chimps is way stronger than ours. We have extremely weak and wimpy bite power. We lost our big teeth, big guts and power to chew and smash food. ● But the fire evidence doesn’t seem to go back far and that is where Wrangham’s critics are hitting him. ● On the other hand, one has to say that when the evidence of the fire vanishes is also consistent simply to the deterioration of the evidence as time passed. The further back you go, 200-300 thousand years, a million to 3 million years, the evidence for anything gets much less because they are washed by floods and erosions and things change. Evidence tends to be eroded with time, so we don’t know how way back fire goes. We know fire goes way back, but we don’t know how far back the evidence for cooking goes. We know that these creatures had fire, so they probably used it for warmth, chase animals away but we don’t know when did that figure out that they could cook food with it. It seems like the kind of thing that could be stumbled across easily. For example, you brought back a dead rabbit from your hunt and threw them around in front of the campfire and you suddenly you rabbit is all scorched and it is softer now and it tastes better. Wranghan found out that other animals, species preferred cooked food if you offer it to them, even wild animals. Whether it is meat or plant material, the animals preferred cooked food. ● With processed food we get fat, same thing with pets. ● We are evolutionary adapted to live only with cooked food, but not with cats and dogs. ● Cats and dogs have the materials, the sharp claws and teeth to eat raw food, supposedly it is healthier for them. Not sure whether it is true. Humans are biologically adapted to eat cooked food ● Summary. Wrangham wants to contradict the old fashion view that cooking has no real effect, it is just an epiphenomenon. ● Cooking is universal, we need it. We have smaller gut. Eating meat does not explain that it makes us humans. ▪ It is universal, it is a need, gut, meat (strikeout, as it did not result in human evolution), time (200,000 years old humans, modern humans us) ▪ His conclusion is that humans are biologically adapted to eat cooked food. Just like how the flea is adapted to drink blood and the giraffe eat leaves on top of trees and so forth. ● What are human adapted for? Nobody can really answer this question. Fruits, yes. Meat, yes. But what we have been missing is cooked food. We all eat cooked food and we have to. ● There are people who don’t eat meat, and they are just as human as we are, they are just as fit and smart and everything. ● The old test, which is the Atwater of digestibility, was based on the idea of what comes out of your rear end, basically all the calories that you eat are gone by the time it gets out on the other end. Therefore, you must have got all those calories. This turns out to be wrong. It turns out that all the calorie information on the food that you buy and eat is in a way wrong, it is misleading. Because that calorie information is based on burning the food. But it says nothing about the calorie information based on whether it is cooked or not or how it is cooked. If you eat a cooked sausage and a raw sausage, the amount of energy that you get out of the same sausage is vastly different. Why? Because your body has to do work that cause energy to digest the food. There is a calorie cost in whatever you eat vs the calorie benefit in whatever you eat. Benefits of eating cooked food (1) energy = more reproduction ▪ Eg: chimpanzees that eat 5% more ripe fruit conceive 4 months quicker ● Cooked food has vastly higher energy than raw. ▪ Body can’t get the same amount of nutrients from raw food. ▪ Cooked food is basically pre-digested. ▪ Cooked food makes it easy for animal guts to digest. We get loads of calories from smaller amount. ▪ Human don’t spend a lot of time chewing every day. We lose the big jaw, teeth and muscle. We don’t need them. (2) Cooking 🡪 energy ● (A) Starch gelatinized 🡪 increased digestibility ● (B) Protein denatured 🡪 increased digestibility ▪ Used to be believe that raw eggs are the perfect food. (Protein denatured 🡪 increased digestibility) ● But it turns out you get very little energy from raw egg. Because your body need to work more to digest. Highly digestibility (cooked!) Up to 97% ● Cooking increases ileal digestibility of egg protein by 44 – 78% ● (C) Texture softened ▪ Tested and proven not only in humans but in animals ▪ Soft diet 🡪 reduced cost of digestion (Secor 2009) ▪ Experiment with snakes: grinded and cooked meat (hard, original, softened) ● Grinding, cooking, grind + cook 🡪 reduction in cost of digestion of 12.4%,12.5% and 23.4% respectively When did humans become biologically adapted to cooked food? ● So, when did this happen? He tried to use fossil records to try to argue that it was somewhere around the time after homo erectus or around the time of homo erectus (1.9 million years ago), that cooking revolution happened and these earlier creatures began to cook, say a percentage of their food, and over a thousand of years a higher percentage of their food is cooked, until such a long period of time of eating this soft, easy to eat, super digestible sort of food, that our species have become absolutely dependent on eating cooked food as we are now. ▪ Interesting changes in skeleton structure and teeth 🡪 teeth get smaller as diet was softer ▪ A great diagram to show the difference in the guts between Lucy (left) with big barrel chest and a narrower rib cage that we find in homo erectus. ● Australopithecus afarensis (walker and tree climber) has bigger guts than homo erectus (walker & endurance runner) (smaller) ● We are totally dependent on eating a cooked diet, we cannot live without it anymore. Our bodies have changed as a result on the kind of diet that we eat, which is cooked. ● Australopithecines like Lucy are creatures that walk on two legs and can still probably climb on trees. The skeletons of homo erectus, the toes and the arch seem to show that they have become expert runners because they are probably powered by a nice breakfast of cooked food, and they hunt for animals (which they failed most of the time), and they went home (empty handed) and the women would feed everyone because they are always out getting dependable food all day like berries, roots and fruits. Meat-eating hypothesis of human origins Consequences of cooking 1) Early Weaning (due to cooking) ▪ Human children 2-3 years old o Consequence: Mother can another baby sooner ▪ Chimpanzee 4 to 5 years old 2) Little chewing 🡪 humans <1 hour per day while chimpanzees take 4 to 7h a day (SAVE TIME) 🡪 because chimpanzees have bigger jaws, guts compared to humans 3) Growing bigger brains 🡪 due to small guts, more energy with cooking 4) Sterilises the food too Our human brain take 20% of our calorie to produce 🡪 eating cook food doesn’t make you clever or give bigger brains BUT eating cooked food makes it possible for bigger brains to grow 🡪 species of human was already born smart (same as smaller guts) 🡺 Did cooked food cause smaller teeth 🡪 no, its because of natural selection where human species born with smaller teeth and jaws will do fine too as they still can eat o Even have a better advantage 🡪 over big teeth cousins as use lesser energy to make it up The cooking hypothesis summary (Richard Wrangham) 1) Humans are biologically adapted to eating cooked food 2) Why? Cooking 🡪 energy 3) When? Since homo erectus ~ 1.8 to 1.9 million years ago 4) Significance 🡪 anatomy, life-history, physiology, society 🡪 he argued that men go out hunting and women stay at home to cook (prof don’t find it convincing) Significance ● Wrangham look for evidence on homo erectus that they are eating cooked food. ● He argued again against the meat-eating hypothesis that meat eating made us what we are and argued that eating cooked food did it. ● Young apes have to be carried around for years. ● Whereas humans, they can reproduce every 2-3 years. Because it is possible for babies to wean early. They can be given mashed food, cooked food. The only time human live on raw food is when drinking mothers’ milk. ● The amount of time freed up from chewing allow us to do other thing. (4-7 hours VS <1hour). The important result of eating cooked diet is that it led to our big brains. ● Our brain is enormously energy hungry. No coincidence that the brain evolved in a creature that eat high energy food. ● Most persuasive point – we cannot live without cooked food and all human beings in the world eat cooked food. ● Cooked food – responsible for bigger brains and smaller guts. ● Rats demonstrated the same things. The ones who ate the soft food gets fat, and the ones with harder food stays thinner because their bodies are burning up more calories just to process the food that they eat. Persistence hunt (ancient form of hunting that still exists today) ● He starts off by observing that only human beings, of all the living things in the world, can recognise tracks on the ground. Other animals can recognise scent but smudges on the grounds mean nothing to other animals, only humans recognise the tracks because we are so clever and can understand what the marks on the ground mean. We used them to chase animals down. ▪ ● ● ● ● ● ● ● ● ● Hand signs indicate that one of them had found the tracks of a group of animals. The persistence hunt – the most ancient hunting technique in the world. The tribe people run down their prey. ▪ They feel the rhythm of the animal’s movement through the spacing in their tracks. ▪ Concentrate on the animal which carry a heavy set of horns 🡪 the animals will get tired more easily. ▪ They separate their target prey from the herd so that its track will not be confused by other animals. After hours of tracking, they go into a trance like state of concentration. If they could not see the tracks of animal, the hunters have to imagine the path the animal would have taken. Next stage of the hunt –the chase. Only one man will undertake the chase – the runner. ▪ This is how a man hunted without weapons, he hunted with physical endurance. Running on 2 feet is more efficient in longer distance than running on four. With hands, the man carry water to replenish himself the liquid which he loses as sweat The moment of the animal’s death, the hunter shared his pain. ▪ He rubbed his legs with the animal’s saliva to relief the agony of his burning muscle and gives thanks to the life he has taken to sustain the lives of his family, waiting for him back in the settlement. These are modern people living in the current society. And this kind of hunting is very likely the earliest form of hunting where they had no weapons, simply their bodies are enough to hunt, having 2 legs to run rapidly. We usually underappreciate our bodies to run long distances with 2 legs. We can run really far with 2 legs, unlike animals. If we chase animals long enough, the animals will die. Summary ● Humans are biologically adapted to eat cooked food only since 1.8 -1.9 million years ago ● Cooked food is massively more energy rich ● We get more energy out from the same food that is cooked than it is raw. ● The part that is most persuasive is the fact that we cannot live without cooked food. ● We lost the structures and abilities to eat raw food because we don’t need them anymore and now, we are trapped. ● Because we start eating cooked food, we cannot get out. We are doomed to continue to eat cooked food as long as we live. ● The thing about adopting a cooked food diet is that our guts are getting smaller and our brains got bigger and these things are somehow linked. According to Wrangham, cooked food is the cause of both, our gut getting smaller and at the same time, our brains getting bigger. ● Lineages evolve, not individuals