Why do you need such hair to avoid overheating?
(Wait - surely you are not suggesting that such hair protects your brain from overheating because the Sun would otherwise beat down on your skull and overheat your brain!)
Encephalization of early hominids
- Thread starter Billy T
- Start date
(Wait - surely you are not suggesting that such hair protects your brain from overheating because the Sun would otherwise beat down on your skull and overheat your brain!)
You've not used Arxiv before?
Yes, you have to download the free PDF, on the right hand side of the screen where it says Download: PDF only (there are often multiple formats available).
You still haven't explained what selection pressure you think it applies. Cooking is a relatively advanced concept (there are modern humans who still haven't grasped it).
The expensive tissue hypotghesis, the one you've been simultaneously butchering and clinging to, is that digestive tracts and your brains are both metabolicly expensive and so there tends to be an inverse correlation between their sizes. There also tends to be (especially among primates) a correlation between fruit consumption and brain size.
Here's what Aiello had to say on the matter:
Brain tissue is metabolically expensive, but there is no significant correlation between relative basal metabolic rate and relative brain size in humans and other encephalized animals. The expensive tissue hypothesis suggests that the metabolic requirements of relatively large brains are offset by a corresponding reduction of the gut. The splanchinc organs [liver and gastrointestinal tract] are as metabolically expensive as brains, and the gut is the only one of the metabolically expensive organs in the human body that is markedly small in relation to body size. Gut sixe is highly correlated with diet, and relatively small guts are compatible only with high-quality, easy-to-digest food. The often-cited relationship between diet and relative brain size is more properly viewed as a relationship between relative brain size and relative gut size, the latter being determined by dietary quality. No matter what is selecting for relatively large brains in humans and other primates, they cannot be acheived without a shift to a high-quality diest unless there is a rise in metabolic rate. Therefore the incorporation of increasingly greater amounts of animal products into the diet was essential in the evolution of the human brain.
Leslie C. Aiello and Peter Wheeler
Current Anthropology
Vol. 36, No. 2 (Apr., 1995), pp. 199-221
The expensive tissue hypothesis does not propose to explain why encephalization occured, but rather the other changes that did (or did not) occur in response to encephalization. Aiello was addressing the question of the mechanics of how encephalization occured, not what drove the encephalization in the first place. In other words, the expenmsive tissue hypothesis was proposed to address a different question.
I agree completely. Said same with fewer words and photo in post 1951 as follows:
... Here is the great primate path divide cooking made:
Have small brain, big gut and eat raw stuff most of the day OR Have big brain & small gut and eat cooked food < 2 hours/ day.
...
And?
Meaningless post devoid of any content, or are you agreeing the Expensive Tissue hypothesis has zero explanatory power with regards to 'Why?' and was examining a different question to the heat stress hypothesis?
I assume the idea of cooking came from some opportunistic eating of some animals that died in a lightning-strike grass fires. Even as result of these unplanned events, a full belly with little effort and efficient digestion provided more energy and provided the time to think after eating all you could hold. I.e. with little energy required either to hunt the eaten animal or to digest it, there was an immediate increase in EROEI (Energy Return On Energy Invested) for that meal.
I don't think there is one advantage, related to more time for thinking, that was selected for, but thousands of different cases where having time to think of better ways of doing things aided survival and procreation. Planned cooking, in contrast, to opportunistic discovery of grass fire cooked animals, requires fire and crude clay pots, for liquids and "roasting sticks." They were not very "advanced concepts;" but improved via use of the "free time" even very primitive cooking provided.
For an imagined example:
One distant ancestor of man, the one who found the grass fire killed animal, say a rabbit, and ate it may have liked both the taste and fact the flames had burnt off the hair, so later when he killed a rabbit, he stuck it on a stick to burn off the hair, etc. and as that worked out well it became his routine, from which others of his tribe learned.
Then some other tribe member doing the same, did not like his hand getting so hot so used a longer stick, but it was more tiring to hold so propped it up on some stones at the mid point with heavy stone at the end far from the fire. Not long afterwards he noticing that the stone pile also blocked all the fires heat from his hand, then later still, a small wall was made, and later the wall went around the fire and rotisserie cooking with just a short stick across opposite walls developed. Then ovens that were first fire heated before the meat was added, etc., etc.
Point of this fictional example is that it takes incremental advances and some years of brain use to make task X more efficient and require less constant attention so as to make even more free time for more thinking about hundreds of other advance in doing Task Y, where Y is one of very many advances that the brain (with time to think) delivered. Each little increment was selected for - became part of an evolving culture.
Let me try another way to answer your question about the selection processes. Consider the evolution of the opposable thumb. What selected for it? Again not any one thing, but thousands of tasks became more efficient, took less time. Were part of a positive feed back cycle.
How would you reply if I asked you to explain what selected for the opposable thumb?
There is no simple single answer to that, or to what selected for a bigger brain - thousands of usually little incremental things did (as they still usually do today). Point is that cooking provided many more hours each day that were no longer needed to find and stuff mouth with low digestion potential food while dragging around a big guts that still was digesting crude raw food eaten a few days earlier.
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No. There is lots of NEW content in the six quotes of post 1951. And as stated in post 1980, there is vast multitude of small incremental / application of thinking that explain why more time for thinking that cooking (and its thought improved advances) made.
BTW, brain is "energy expensive tissue" - that is a fact, not a hypothesis. Roughly 10 times greater energy per Kg is required than the rest of the body.
Long ago, I said I did not want to continue this off thread detour and suggested it should continue as a conversation. Unless you do answer the parallel question I asked you about what explains selection for the opposable thumb, I don't plan to post more here, off thread, even if you and others wish to.
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And yet you're willing to dismiss, out of hand, a hypothesis that is backed by evidence, ties in nicely with some of the other hypotheses (eg social pressures and more efficient hunting and gathering) as well as the expensive tissue hypothesis all so you can try and bash a square peg into a round hole?
Here's what I think happened, based on the research I have done.
Heat stress selects for larger brains with greater interconnectivity to allow greater levels of cognitive function in an arid environment.
The improved interconnectivity allowed for more efficient hunting and gathering, which combined with social pressures selected for more complicated uses of existing tissue.
More complicated uses required the brain to expand and increase interconnectivity in order to retain the heat resistance and redundancy, and required more energy. Increasing metabolism is less favourable than improving digestive efficiency and hunting and gathering methods because it raises core temperature which exacerbates rather than relieves core temperature issues. Improving digestive efficiency, improving hunting and gathering methods, and improving food preparation methods in turn allows the reduction of gut size which is selected for becuase it reduces the over-all additional energy requirements of the organism. Improving hunting and gathering techniques, and improving food perperation techniques, in turn, represent more complicated uses of brain tissue, which requires brain size to increase, which in turn require further growth and interconnectivity to retain, or improve upon existing heat stress resistance. Increased socialization and communication skills are selected for because they encourage more efficient hunting and gathering skills as well as food preperation skills.
And so a positive feedback cycle is established which drives an increase in brain size and the compelxity of brain function until a critical level is reached related to social development and language development - at which point development slows or stops because the need for increased specialization and complexity is removed.
See - you don't understand the square peg you're cramming into a round hole:
...The expensive tissue hypothesis suggests that ...
Those are the words of the original author, not me - take it uyp with them if you don't like it.
The idea of cooking, from whatever source derived, requires a brain capable of deriving such ideas.billy said:
Be much easier and tastier to skin the rabbit, and easier to capture the rabbit using fire in the first place (which delivers one's food precooked), but let's go with the scene:billy said:
So you are imagining a bipedal tool and weapon constructing hominid routinely capable of controlling fire and successfully hunting such prey as rabbits without the physical attributes otherwise necessary, a member of an entire tribe of hominids capable of picking up that specific trick and making their own weapons and cooking spits for using it with their own fires and captured game, by observation.
So you are already talking about a predator living in very capable pack op weaponized and fire-equipped hominids - i.e. small gut and high quality food consumer, with lots of leisure time - capable of planning and conceptualizing such a task - i.e. large brain, significantly more expensive than a chimps.
From there to us is not that big a jump. It's getting to that level, from chimp level, that needs explanation. That's a very big jump.
I would search for possible explanations that provided incremental advantage to incrementally greater opposition starting with the hand structure of an arboreal primate.billy said:
There are several easily postulated - more reliable and energy efficient carrying of objects or children by an early stage quasi-biped, maybe, or better foraging grip on shallow water food items, stuff like that.
I would not guess easier net weaving or complex tool manufacturing and employment, and the like, because such things would require a basically opposable thumb in the first place.
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Moderator Note: Problem solved.
Huh? What requirement can not be met with raw food?
The issue of the egg before the chicken can not so easily be dismissed in a organic system that requires bio feedback loops to function and the evolution of successful bio feedback loops to achieve a sustainable evolution. IMO
As explored in the Art House Sci Fi screen play: 2001: A Space Odyssey (Arthur C Clarke: 1968) the massive leap into self determination, volition, sentience ( the use of abstraction ) is not to be underestimated.
The ability for the human to decide to suffer for how long and how much, plays a key role. Example: "I shall wait and have this for breakfast" or "Wait till I get you home!
" or "I shall climb that mountain to see what I can see" etc requires self determination as does cooking and advanced use of abstraction ( imagination).These faculties do not come cheap IMO.
yes evolution doesn't come cheap!
The primary faculty of the big brain Human IMO is the ability to imagine thus we generate a subjective and virtual world in which we can make free choices and then apply that virtual world to our greater reality. ( as in rehearsal, practice before doing, hypothesizing, theorizing, visualizing an act before doing it etc...
But alas, you are left with the "egg before the chicken or the chicken before the egg" problem and simply hypothesizing a co-development over millions of years for a fully integrated bio feedback system doesn't hold water too well IMO.
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sorry ...Trippy can you move my last post as well
Sure. But at this point it won't be until after work.
Bells
Staff member
If Billy is buying into Richard Wrangham's theory, then that is the exact theory he is buying into.
There are obvious caveats with this theory, principally when hominids first actually tamed fire to use for cooking and what exact correlation that had with brain development. Not to mention how Wrangham first came up with the theory in the first place:
Richard Wrangham has tasted chimp food, and he doesn’t like it. “The typical fruit is very unpleasant,” the Harvard University biological anthropologist says of the hard, strangely shaped fruits endemic to the chimp diet, some of which look like cherries, others like cocktail sausages. “Fibrous, quite bitter. Not a tremendous amount of sugar. Some make your stomach heave.” After a few tastings in western Uganda, where he works part of the year on his 20-year-old project studying wild chimpanzees, Wrangham came to the conclusion that no human could survive long on such a diet. Besides the unpalatable taste, our weak jaws, tiny teeth and small guts would never be able to chomp and process enough calories from the fruits to support our large bodies.
Then, one cool fall evening in 1997, while gazing into his fireplace in Cambridge, Mass., and contemplating a completely different question—“What stimulated human evolution?”—he remembered the chimp food. “I realized what a ridiculously large difference cooking would make,” Wrangham says. Cooking could have made the fibrous fruits, along with the tubers and tough, raw meat that chimps also eat, much more easily digestible, he thought—they could be consumed quickly and digested with less energy. This innovation could have enabled our chimplike ancestors’ gut size to shrink over evolutionary time; the energy that would have gone to support a larger gut might have instead sparked the evolution of our bigger-brained, larger-bodied, humanlike forebears.
Then, one cool fall evening in 1997, while gazing into his fireplace in Cambridge, Mass., and contemplating a completely different question—“What stimulated human evolution?”—he remembered the chimp food. “I realized what a ridiculously large difference cooking would make,” Wrangham says. Cooking could have made the fibrous fruits, along with the tubers and tough, raw meat that chimps also eat, much more easily digestible, he thought—they could be consumed quickly and digested with less energy. This innovation could have enabled our chimplike ancestors’ gut size to shrink over evolutionary time; the energy that would have gone to support a larger gut might have instead sparked the evolution of our bigger-brained, larger-bodied, humanlike forebears.
Jokes aside, the theory, is one that is gathering steam, led by one Suzana Herculano-Houzel, a neuroscientist in Brazil, and Manuel Domínguez-Rodrigo, from Spain, if latest studies are anything to go by. Just as the theory has a lot of detractors, with evidence of controlled fire that would have been used for cooking, not quite supporting the cooking for brain size brigade. One thing that Billy is arguing about, in this thread, is that it is now very popular among the paleo diet supporters and is being embraced by them, which could be why it has gathered so much steam of late.
But this still just remains a theory and it has a lot of hurdles to overcome before it becomes more widely accepted in the scientific community.
Nothing with a chimp brain can learn to cook. That's the main problem - it's the initial bump up, from the chimp brain to the size where all this feedback benefit from fire and tools and such can start to happen, that is the hardest to explain.
Cooking comes into the picture after that - it works as a later contribution to the jump from chimp-and-a-half to basically human.
Also: We were bipedal, which implies a somewhat smaller gut, and probably had opposable thumbs, before we hit the initial brain size jump. So there's that to consider. We were not eating a chimp diet, even then - we had some kind of foraging niche of our own.
Bells
Staff member
I agree.
Cooking and brain size might correspond with the second burst of brain growth in our evolution, but not the first (and I say that with a huge might). There is no evidence that our early chimp like ancestors were using fire to cook. The evolution of the teeth from our very early ancestors should be proof of that.
Fraggle Rocker
Staff member
The earliest evidence of controlled fire goes back almost a million years. That was long before the emergence of H. sapiens. Therefore this key technology was indeed developed by an ancestral species with a smaller brain.
Other key technologies were developed even earlier. Flint knapping, for example, allowed our distant ancestors to scavenge the meat left on the bones of animals killed by predators, since their teeth were not properly shaped for the job. This greatly increased the protein content of their diet, making it possible for descendants with a mutation for larger brains to survive--since brain tissue requires a lot of protein for maintenance.
(This is why dogs, who have been bred to enjoy an omnivorous diet, have smaller brains than wolves.)
Hairless primates, namely humans, that have cooked food, and thus do not need huge gut with long transit times to digest food eaten raw, as apes do. So apes have relatively small surface to volume ratio (compared to "hairless apes") for cooling. Thus, humans can more efficiently dump more heat to the environment, especially as even weak air currents, unimpeded by a cm of thick hair (or fur) increase the rate of cooling by evaporation (perspiration).
Digestion of food eaten raw, is much more energy intensive process than digestion of cooked foods, which have been soften and partially broken down into smaller molecules by the external heat (stove or fire). Thus not only is there many more cubic centimeter of "ape gut" than human gut, the energy each cm^3 uses to a break down complex molecules into smaller units that can pass thru the intestine walls, into the blood is greater too. Then there is also the fact that the ape gets a smaller fraction of the calories from the raw food with his less efficient digestion of it and it takes longer , still requiring energy before it leaves his body.
All these factors make the apes thermal problems worse as his cooling surface to gut heat production is a smaller ratio than that of human. I doubt an ape could survive in the full noon sun light, if you shaved all his black hair off and let almost all of the solar heat of the African plains reach his skin. A very high fraction of the sun's heat is absorbed by the ape's black hair and quickly transferred to the air, not the ape's body. Most humans don't need to block sunlight from reaching their body FOR THERMAL REASONS*; however, humans who live in or transit hot solar deserts keep most of their body covered with more than one layer of cloth. For one who does not understand what I have been explaining about the importance of NOT letting the solar heat get to the body, this use of thick layers of cloth by the Bedouin and other desert Arabs seems strange.
* Skin cancer is a different reason.
As one of my six references in post 1951 explicitly said (and all imply): Raw food and its required large volume and large energy requirement gut, leaves too little energy left over to have a big high energy demand brain too. That is also the answer to your question below, so I only summarize after it.
It is impossible to get from raw food the energy needed to support BOTH the raw food's required big, energy-intensive, gut and longer processing period (days, not hours, of transit time) with only a fraction of its calories released in the inefficient digestion, (done only by the body), instead of with pre-softening and some external partial break down of complex molecules by cooking; AND the very energy intensive requirement of large, human size brain. Elephants can do this as they have evolved an "auxiliary cooling system" - huge ears, and larger ears for the African elephant than the Indian elephant as African elephants are under greater peak heat stresses.
Also bigger brains (of same nearly spherical shape for shorter inconnection white mater) have a worse thermal stress than smaller brains do as both their surface to volume ratio is lower AND internal cooling by blood flow thru the brain, especially the small capillaries, is dissipative - I.e. more heat generate by the blood flow which it must remove. Frankly, I think the "thermal stress" argument as the cause of bigger brains has every thing just backwards. Please, some one, explain why bigger brains relive / reduce thermal stress.
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