Encephalization of early hominids

[Billy T]

... Given the dire circumstances facing the world with climate change etc, the threat of suffocation and human nature I would be highly skeptical that 23% is actually a valid percentage of atmospheric O2
Where do they get this figure from any way?

It is easy to measure for any gas mix with O2 the only oxidizer. Just measure the pressure is a closed container before and after passing electric current thru wire in the container, is how this physicist would do it. I.e. as red hot wire grows thinner the resistance will increase. When that stops, turn the current off an let internal temperature return to the original temperature. The pressure will then be lower as all the O2 is now in the metal oxide. - I bet chemists have even better ways.

Your assumption that extinction will be by "suffocating" (lack of O2 or excess of CO2) is almost surely wrong. With AGW, both the peak temperature and humidity are increasing. When the wet bulb temp is 35C (95F) for an hour of exposure to that, you die. - internally over heat as can't dump to the environment your metabolic heat, even if just sitting in a chair.* Dogs can only perspire via their tongues, so they will all die before you who can perspire with most of you skin doing so.

Humans, not in "couch potato" mode but in their ancient state are really good running machines. Could run all day long after many animals that could not perspire via their skin. They eventually died of internal over heating. - I believe this is a main factor in why man became the dominate creature, not his bigger brain, which had not yet become "bigger."

Then he learned to cook roots etc. so didn't need to spend most of his awake hours munching on leaves etc. as apes do between his infrequent animal kills. With "free time" the discovery of cooking gave, his small brain became larger and useful and improved with use plus evolution selection, but it all started with being the world's best running machine.

* the rich will have air conditioning but that soon fails when linemen can't remove tree branches from wires etc. - no food delivered etc.

 

[iceaura]

Could run all day long after many animals that could not perspire via their skin. They eventually died of internal over heating. - I believe this is a main factor in why man became the dominate creature, not his bigger brain, which had not yet become "bigger."

Several researchers have noted that an initial enlargement of the human brain was possibly an adaptation to heat exertion - running, etc, under the afternoon sun of Africa, a time of day when humans could forage and scavenge away from the trees without fear of the big cats and other heat - vulnerable animals. Redundant brain circuitry is a known heat adaptation, helping to stave off seizures and brain failure from what is in effect an induced fever.

In this postulation, the initial enlargement created extra capacity during cooler times, which could be employed in managing further exertions in the heat - longer distance travel and exertion towards a goal distant in time or space, especially under duress, requires and then rewards a brain more capable of imagination and extrapolation. So an evolutionary feedback loop is created, the results of which create all kinds of possibilities for the use of that extra capacity.

The interesting aspect of that possibility is its incremental reward for incremental increase in brain size - which handles the puzzle of how the extra expense of the large brain, which is huge, was overcome in the absence of the tools, language, and other advantages that pay for our big brains today.

 

[Billy T]

Several researchers have noted that an initial enlargement of the human brain was possibly an adaptation to heat exertion - running, etc, under the afternoon sun of Africa, a time of day when humans could forage and scavenge away from the trees without fear of the big cats and other heat - vulnerable animals....

Certanly that "brain is for cooling" POV was held by the ancient Greeks. They knew its blood flow was large compared to its mass, but thought the heart was origin of thoughts, not the brain. - That belief is still reflected in language.

What you state makes little sense to me. Do you have a link stating that? The adaption* to heat stress would be increased density of skin's sweat glands, not a large brain. I think human brain became larger ONLY, when our ancestors had time to use it, time to sit and think, rather than spend almost every day light hour trying to find or catch food so as not to starve.

When our ancestors had not yet leaned their clay pots could be put in the fire to cook food, the digestive processes available to them were much slower and less efficient. - Like apes of today, they had to spend most of the day light hours eating raw stuff as you go / find it. No time to do much planning / thinking etc. That "free time" for bigger brain becoming useful / selected for/ came only after cooking of food make digestion quicker and much more efficient. - Greatly reducing the volume of stuff you needed to find and stuff in your mouth. The invention of cooking was the great step forward to a bigger brain's evolution.

* "Adaption" is the wrong word. It would be evolutionary selection of individuals with better sweat cooling systems, not bigger brains, prior to discovery of cooking.

 

[iceaura]

What you state makes little sense to me. Do you have a link stating that? The adaption* to heat stress would be increased density of skin's sweat glands, not a large brain.

A larger brain would not be for cooling, but for resistance to collapse under heat stress - redundant circuitry helps, there.

I think human brain became larger ONLY, when our ancestors had time to use it, time to sit and think, rather than spend almost every day light hour trying to find or catch food so as not to starve.

Very few large organisms, none of them omnivores or predators, spend most of their time actively trying to find or catch food so as not to starve. That would be an unstable and soon to be destroyed ecological niche. If an organism has insufficient surplus time under normal circumstances, the inevitable occasional hardships will kill it. Our small brained ancestors spent plenty of time sitting around at leisure, as baboons and chimpanzees do today, or they would never have survived. And yet their brains remained small, for hundreds of thousands of years.

Brains are very, very expensive. They are seldom worth their keep past a certain minimum size - an organism generally wants the smallest brain it can get by with. Something had to begin incrementally rewarding an incrementally bigger brain in a small number of individuals of an already long established hominid species, to cause us. And that something could not have been the kinds of culturally mediated benefits we enjoy today.

Supply side evolution - the approach that opportunity will drive evolutionary progress - works no better than supply side economics.

btw: Civilized human beings spend much more time working - engaged in onerous but economically productive effort - than their primitive ancestors did. The anthropologists who put stopwatches on the San hunter gatherers in the 50s and 60s estimated the men worked between 2 and 4 hours per day, about 20 per week, and the women half again as much - and these were marginal folk hanging on in very inhospitable terrain, with an extreme amount of effort demanded of them.

 

[Billy T]

A larger brain would not be for cooling, but for resistance to collapse under heat stress - redundant circuitry helps, there. ...

Large or small brain would have same temperature - that of the blood flowing thur it.

For me your "redundant circuitry" is not clear what that means - possible could make for conflicts - one part saying "flee" and other saying "fight" when new danger arose. Perhaps three independent processor doing same task with majority rules when difference arise is better but not cost effective, I am almost sure.- Can you clarify?

 

[iceaura]

For me your "redundant circuitry" is not clear what that means - possible could make for conflicts - one part saying "flee" and other saying "fight" when new danger arose. Perhaps three independent processor doing same task with majority rules when difference arise is better but not cost effective, I am almost sure.-

Not error but failure is the problem. The hypothesis is that a brain with multiple sets of neurons running in parallel for control of critical functions (breathing, swallowing, adrenal gland output, heart rate and timing, coordination of voluntary muscle contraction), any one of which is minimally sufficient to respond to a given stimulus with proper output signal, is less likely to fail under heat stress.

The principle of guarding against heat stress failure by incorporating redundant circuitry is standard in integrated circuit design. http://users.ece.cmu.edu/~koopman/des_s99/electronic_electrical/

The principle of evolutionary advance via duplication of existing structure and subsequent adaptation of role under selection pressure is also standard. It's an easy evolutionary path - given the selection pressure.

Cost effectiveness depends on the cost of failure, no?

 

[Billy T]

Not error but failure is the problem. The hypothesis is that a brain with multiple sets of neurons running in parallel for control of critical functions (breathing, swallowing, adrenal gland output, heart rate and timing, coordination of voluntary muscle contraction), any one of which is minimally sufficient to respond to a given stimulus with proper output signal, is less likely to fail under heat stress.

The principle of guarding against heat stress failure by incorporating redundant circuitry is standard in integrated circuit design. http://users.ece.cmu.edu/~koopman/des_s99/electronic_electrical/

The principle of evolutionary advance via duplication of existing structure and subsequent adaptation of role under selection pressure is also standard. It's an easy evolutionary path - given the selection pressure.

Cost effectiveness depends on the cost of failure, no?

I don't think what works for electronic circuits works for the analog brain. - No neuron is critical. Thousands die every second. If there were two parallel sets of nerve networks telling heart when to beat that could, and probably would, kill you. I don't want to continue more this already too long a detour - start a conversation, if you do.

 

[iceaura]

I don't think what works for electronic circuits works for the analog brain. No neuron is critical.

1) It's standard design for critical analog electronic circuits. 2) The brain is largely digital. 3) All the circuits at risk involve many neurons, and fail as collections of neurons.

If there were two parallel sets of nerve networks telling heart when to beat that could, and probably would, kill you.

There is considerable redundancy in the heartbeat control modules, and it doesn't kill you - instead, it protects you against small localities of malfunction, such as the early stages of heat stress cause.

. I don't want to continue more this already too long a detour

OK. But the point that people are by evolutionary and historical standards being overworked in modern times is worth contemplating, as possible responses to AGW threat come up for consideration.

 

[Billy T]

... There is considerable redundancy in the heartbeat control modules, ...

Not in the brain. There is cascaded redundancy: If brain signals do not stimulate the Sinal Atrial Node (Spelling from memory) for too long, the S.A.N. will imitate a pulse on its own. That pulse travels down the His fibers (Bundle of His) to lower aspects of the heart. If conduction in the His path fails then lowers parts of the heart will contract. Unfortunate not well coordinated, but perhaps you can live long enough to get a pace-maker implanted.

This not the brain redundancy you spoke of. It is more like ship. If the ship start to sink then the lifeboats take on the job. If they leaks, then the life vest take on the job, If it water logs then you swim. Nothing in either case (Heart or ship) is parallel redundancy.

 

[billvon]

Not in the brain. There is cascaded redundancy: If brain signals do not stimulate the Sinal Atrial Node (Spelling from memory) for too long, the S.A.N. will imitate a pulse on its own. That pulse travels down the His fibers (Bundle of His) to lower aspects of the heart. If conduction in the His path fails then lowers parts of the heart will contract. Unfortunate not well coordinated, but perhaps you can live long enough to get a pace-maker implanted.

Ice is quite literally correct. There are a large number of parallel functional pathways to ensure heartbeat. For example, dozens of nerve fibers in the vagus nerve provide downregulation to the heart; a similar number in the accelerans provide upregulation. If a few die your heart is still regulated. You can remove part of the SA node and still have it perform its function because it is massively parallel.

If there were two parallel sets of nerve networks telling heart when to beat that could, and probably would, kill you.

There are. And indeed such parallelism is often a problem; google "re-entrant pathways" to see how the heart's massive parallelism can sometimes work against it.

 

[iceaura]

... There is considerable redundancy in the heartbeat control modules, ...
Not in the brain.

Yes, in the brain.

There is also extra capacity in the SAN, and in the direct response firing synapses on the heart itself.

But the interesting extra capacity would be the hypothetical overgrowth the heat stress hypothesis imagines to have emerged in the parts of the brain handling conscious thought and environmental awareness - these redundancies would be incrementally beneficial to a being with a foraging strategy involving long distance exertion and complex decision making at midday across African grasslands.

And then they would be available, during leisure hours, for conscious thought and complex awareness of no immediate benefit.

 

[Billy T]

Ice is quite literally correct.

No, not in the brain are there parallel excitation sources for the heart, unless you want to say the many neural cells sending signals to the vagus nerve are independent parallel systems OR that the vagus nerve, which has many individual nerve fibers (axons) carring their excitation down to the heart is as many systems as there are axons in the vagus nerve. You did make this second silly claim that parallel axons of a nerve bundle, should be considered parallel systems.

There are a large number of parallel functional pathways to ensure heartbeat. For example, dozens of nerve fibers in the vagus nerve provide downregulation to the heart...

It is ONE vagus nerve we consider as the path way not its few hundred axons for individual cells that are parallel systems. As you take that POV that every one of the cells driving signal down those axon is a separate parallel system too, then the brains does have sever hundred parallel system stimulating the heart, but why stop there - each of those cells driving action potential down an axon was in turn part of a neural oscillator network with more than a million cells - I.e. Why not claim there are at least a million distinguishable cells that work in parallel to stimulate the heart? - Answer: because that is a silly reductive POV. The heart is normally stimulated to beat by the (one) vagus nerve. We distinguish nerves from the axons that make them up. E.g. each eye has ONE optic nerve system.

Once we consider the Atrio Ventrial part of the heart, AV then yes there are two independent and physically separate parts of the AV that can drive, stimulate via His conduction fibers, the lower parts of the heart. That is where a mesh like electrode of heart pacer is attached. Although I know a lot about all this as helped develop the first good reliable pacemaker, which APL/JHU then licenses to MedTronics (and they made millions form it) I did follow your suggestion (as I have forgotten a lot in ~30 years since leaving that project.) But first let me clarify a point that is often is not mentioned: the AV node is a "triggerable one-shot oscillator" - normally one cycle produced for each brief and weak stimulation from the brain. I. e. the output of the AV node is much stronger and longer lasting than the pulse that triggered it. Its output goes down the fast conduction bundle of His to cause the lower ventral parts of the heart to contract.

Here, from first Google hit (Wiki) are some of the first facts stated, which illustrate my point well - namely two parallel systems for making heart contract don't normally exist as when they do they can cause problems even death:

... atrioventricular nodal reentrant tachycardia, AVNRT, is a type of tachycardia (fast rhythm) of the heart. It is a type of supraventricular tachycardia (SVT), meaning that it originates from a location within the heart above the bundle of His. AV nodal reentrant tachycardia is the most common regular supraventricular tachycardia. ... The main symptom is palpitations.

AVNRT occurs when a reentry circuit forms within or just next to the atrioventricular node. The circuit usually involves two anatomical pathways: the fast pathway and the slow pathway, which are both in the right atrium. The slow pathway, which is usually targeted for ablation, a treatment for AVNRT) is located inferior and slightly posterior to the AV node, often following the anterior margin of the coronary sinus. The fast pathway is usually located just superior and posterior to the AV node. These pathways are formed from tissue that behaves very much like the AV node, and some authors regard them as part of the AV node.

In common AVNRT, the anterograde conduction is via the slow pathway and the retrograde conduction is via the fast pathway ("slow-fast" AVNRT).

Because the retrograde conduction is via the fast pathway, stimulation of the atria (which produces the inverted P wave) will occur at the same time as stimulation of the ventricles (which causes the QRS complex). As a result, the inverted P waves may not be seen on the surface ECG since they are buried with the QRS complexes. ...

Let me amplify this:
"The slow pathway, which is usually targeted for ablation, (a treatment for AVNRT) is located inferior and slightly posterior to the AV node"
and explain why we have a second way to stimulate the lower parts of the heart even though it can and does cause the very problems as I noted when two differnent systems can cause the heart to contract."

It is possible for the brain signal intended to trigger one shot from the AV node is too weak or non-existent. Thus nature has provided an alternative way to keep the heart beating at least at a slower rate. If it has been too long since the normal AV node was activated, then within the AV is another self activating single pulse generator but not strong enough by its self to cause the ventricle parts of the heart to contract. Thus as this backup generator is below the AV node, it sends it signal retrograde to trigger the needed stronger AV node half cycle of that one-shot oscillator and keep you from dying.

Perhaps an analogy will help: We put life boats on ship in case something goes wrong, but they can cause something to go wrong. For example in a storm, the ropes holding one end of the life boat can break allowing it to swing free and punch some holes in the hull so that the storm's larger waves enter making ship float lower and fill with water faster until it sinks. Before that happens, the captain will order it cut free. Life boats, even though part of the ship are not a parallel floatation system, but a backup system to be used SEQUENTIALLY if the primary system fails.

AVNRT is caused by a backup system than often saves lives, but if the backup pulse to the AV node is not needed as brain is triggering the AV node OK, and the backup system is active too, then you have two systems trying to control the heart's beating. Best to destroy one - the backup one (Ablate it, with well localized heating as it is distinct tissue like the life-boats are. Laser heating is used now days, I think). AVNRT seldom kills but will if it converts to ventricular fibrillation* as it often does if the AVNRT is not just a few cycles of heart beat rhythm - last for a minute or so.

Thanks for directing me to link that illustrates well how two different systems trying to control heart beat is NOT nature's plan. - Do not exist in the brain as I stated. That does not rule out backup systems which do exist - at least three for heart beat.

*BTW my group at APL/JHU made a much larger implanted device that could terminate automatically ventricular fibrillation. I did not work on that project but followed it closely. MedTrons also sells that APL designed device. We called it AID, for Automatic Implantable Defibrillatior, but after AIDs had a differnent meaning, MedTronics renamed it. It would try three times to stop the ventricular fibrillation. Gave each internally delivered shock about 10 seconds apart as we had to recharge the energy storage capacitors. This meant by standers would see the victim convulsing three times.

We knew lawyers would fight each other for the right to claim APL had killed him; so we included a "bucket memory" - several times each second the data in bucket n transferred to bucket n+1 and eventually was lost as the last bucket in the chain got new data. - We could proof in court that victim was in ventricular fibrillation 5 seconds before our device tried even the first of three times to save him. In that era, this added to the cost and volume. We did not want to tell real reason it was needed** - So said it was for medical research - provided EKG data for 5 or so seconds before ventricular fibrillation began.

** No doctor would implant one and no company would make one without that bucket memory, as quiet often the victim of ventricular fibrillation does die - even with automatic intervention in a few seconds. They did not want many dozens of multi-million dollar law suits each year. In airport hall way you can see ventricular defibrillation boxes now. I would not use one on anyone - I'm not a doctor. Only a doctor, with stethoscope,*** would stand a chance of not losing very cent he had if the victim did not live. - That is the world we live in today: Of the lawyers, for the lawyers and by the lawyers. (You can replace "lawyer" with "very rich" to be more general.)

*** And a dam good, expensive lawyer with hours of documentation on sexy Power Point slides about ventricular fibrillation.

 

[billvon]

No, not in the brain are there parallel excitation sources for the heart

Again, of course there are. Your central nervous system is one of the most massively parallel processors on the planet. That's why people regularly lose lots of neurons to head impacts, senescence, apoptosis, tumors, hypoxia etc and do not have their hearts go out of regulation. Specifically, you can remove parts of the pons and not lose such regulation. (Remove all of it, of course, and you are out of luck.)

unless you want to say the many neural cells sending signals to the vagus nerve are independent parallel systems OR that the vagus nerve, which has many individual nerve fibers (axons) carring their excitation down to the heart is as many systems as there are axons in the vagus nerve. You did make this second silly claim that parallel axons of a nerve bundle, should be considered parallel systems.

Why is it silly? Aircraft have multiple parallel fly-by-wire control systems. Their wiring is often contained in common looms - just as the multiple parallel control systems for the heart are contained within common nerves.

It is ONE vagus nerve we consider as the path way not its few hundred axons for individual cells that are parallel systems.

See above.

 

[Trippy]

I saw an article very recently suggesting that the evolution of large brains in human ancestors may have been an evolutionary adaptation to heat stress, just as Bilvon is saying. The corrollary being that when heat stress was less of an issue, all of a sudden we found ourselves with all this redundant circuitry that we then started putting to other uses.

 

[iceaura]

No, not in the brain are there parallel excitation sources for the heart,

The issue was redundancy, not separate parallel structure only. Significantly more neurons than are needed, any small subset of which are sufficient for the original function, is what was posited. That is a standard method for improving circuit function reliability in circumstances of occasional heat stress, and it's an easy path for evolutionary change to take.

The corrollary being that when heat stress was less of an issue, all of a sudden we found ourselves with all this redundant circuitry that we then started putting to other uses.

And that would have happened immediately, since heat stress in a midday forager/scavenger or persistence hunter would be an occasional and fairly brief demand however severe.

And the "other uses" would have been, in the beginning, exactly the uses that most needed protection under the immediate stress - imagination, forethought, terrain memory, narrative development and maintenance, everything necessary for successful long distance hunting and/or scavenging.

Meanwhile, back at the camp: most omnivores and predators, as humans emerging from the trees unto the hot savannah are presumed to have been, have a lot of leisure time in their ordinary life. They sleep a lot. And it is very unlikely that the brain modifications involved would have been narrowly confined to any one sex or age classification.

This is far from the thread, of course, but the official thread topic is just debris and dishonesty from the corporation-addled wingnut web sites of the English speaking world - so it doesn't need much attention. We have leisure time, and no immediate stress.

 

[Trippy]

I saw an article very recently suggesting that the evolution of large brains in human ancestors may have been an evolutionary adaptation to heat stress, just as Bilvon is saying. The corrollary being that when heat stress was less of an issue, all of a sudden we found ourselves with all this redundant circuitry that we then started putting to other uses.

As I understand it, the basic idea was proposed in the 1970's.

Take a fixed resource, a waterhole, and put humans around it. The humans also have to spend time solitary hunting a mobile resource - prey, including endurance running. There is a fixed distance, beyond which a hunter can not proceed and still be successful because they would die of dehydration returning (unless the hunt is successful) to the camp because chasing prey induces heat stress and the consumption of the body's water resource.

Heat stress causes neuron death so, ultimately, those hunters that are more successful would be expected to be those that have larger brains with greater neuron interconnectivity, that have sufficient redundancy to retain sufficient appropriate processing capacity and is therefore more resitant to heat stress and the damage it causes. This seems more viable given that runners can get body temps of up to 42°C and heat stroke victims have had body temperatures recorded up to 47°C which is higher than animal models would seem to suggest.

This also seems to suggest a natural reason why the exponential growth of the human brain would stop with the emnergence of speech - co-operative hunting might be expected to become more successful than solitary hunting.

 

[Trippy]

The issue was redundancy, not separate parallel structure only. Significantly more neurons than are needed, any small subset of which are sufficient for the original function, is what was posited. That is a standard method for improving circuit function reliability in circumstances of occasional heat stress, and it's an easy path for evolutionary change to take.

And that would have happened immediately, since heat stress in a midday forager/scavenger or persistence hunter would be an occasional and fairly brief demand however severe.

And the "other uses" would have been, in the beginning, exactly the uses that most needed protection under the immediate stress - imagination, forethought, terrain memory, narrative development and maintenance, everything necessary for successful long distance hunting and/or scavenging.

Meanwhile, back at the camp: most omnivores and predators, as humans emerging from the trees unto the hot savannah are presumed to have been, have a lot of leisure time in their ordinary life. They sleep a lot. And it is very unlikely that the brain modifications involved would have been narrowly confined to any one sex or age classification.

This is far from the thread, of course, but the official thread topic is just debris and dishonesty from the corporation-addled wingnut web sites of the English speaking world - so it doesn't need much attention. We have leisure time, and no immediate stress.

Agreed.

 

[Billy T]

I saw an article very recently suggesting that the evolution of large brains in human ancestors may have been an evolutionary adaptation to heat stress, ...

Link please. Also if 5 or more years old, it is in conflict with new idea of the 6 links below (all quality sources) and final video.

our ancestors managed to get enough energy to grow brains that have three times as many neurons as those in apes such as gorillas, chimpanzees, and orangutans. How did they do it? They got cooking, according to a study published online today in the Proceedings of the National Academy of Sciences.

The brain is so energy-hungry that in humans it represents 20% of the resting metabolic rate, even though it only represents 2% of body mass, suggest Professor Suzana Herculano-Houzel and Karina Fonseca-Azevedo of the Institute of Biomedical Sciences at the Federal University of Rio de Janeiro.

"Why are the largest primates not those endowed with the largest brains as well? Rather than evidence that humans are an exception among primates, we consider this disparity to be a clue that, in primate evolution, developing a very large body and a very large brain have been mutually excluding strategies, probably because of metabolic reasons."

Gorillas, they suggest, already live on the limit of viability, foraging and eating for 8.8 hours a day, and in extreme conditions increasing this to as much as 10 hours a day. In contrast, humans' move to a cooked diet, possibly first adopted by Homo erectus, and their bigger brains yet smaller bodies, left spare energy which allowed further rapid growth in brain size and the chance to develop the big brain as an asset rather than a liability, through expanded cognitive capacity, flexibility and complexity.

Eating meat and cooking food made us human, the studies suggest, enabling the brains of our prehuman ancestors to grow dramatically over a period of a few million years. Although this isn't the first such assertion from archaeologists and evolutionary biologists, the new studies demonstrate, respectively, that it would have been biologically implausible for humans to evolve such a large brain on a raw, vegan diet

The idea is that raw food just doesn't provide enough calories. You have to get out more than you put in, and raw food takes a lot more work (meaning calories) for your muscles and organs to chew and digest, resulting in a net decrease in the amount of calories available for the rest of your cells. But you can only spend so many hours of the day eating--there must be time to sleep, forage and procreate, too. This limits the amount of calories you can get per day, and it turns out this is directly related to how many neurons you can grow

cooking—thanks to chemical processes that differ for starches, meats, and connective tissue—increases the number of calories in the food available to the human digestive system. Cooking also reduces the energy cost of digestion: gorillas, for example, must chew all day to absorb enough nutrition. Cooking makes more metabolic energy available for other things: the development of a large brain relative to gut size, or later, in prehistoric societies, more time available for hunting.

"You can't have a large brain and big guts at the same time," explains Leslie Aiello, an anthropologist and director of the Wenner-Gren Foundation in New York City, which funds research on evolution. Digestion, she says, was the energy-hog of our primate ancestor's body. The brain was the poor stepsister who got the leftovers.

Caption is: As we began to shy away from eating primarily fruit, leaves and nuts and began eating meat, our brains grew.

We developed the capacity to use tools, so our need for large, sharp teeth and big grinders waned. From left, a cast of teeth from a chimpanzee, Australopithecus afarensis and a modern human.

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.

Watch Harvard professor of biology and anthropology's video at:
http://bigthink.com/videos/cooking-changed-the-size-of-our-brains
It makes my point too and another I did not think of: Cooking's much higher nutrition for much less work also made free time for many more well-feed healthy babies that survived to make more. - An explosion of the hairless ape's population followed.

 

[iceaura]

Link please. Also if 5 or more years old, it is in conflict with new idea of the 6 links below (all quality sources)

None of those links is in conflict with the heat stress hypothesis for the initial incremental boosting in brain capacity and size.

As in the other standard explanations for brain development that depend on factors that require a larger brain in the first place, cooking has a chicken and egg problem in explaining the initial boost - the increase beyond the chimpanzee volume and energy consumption. That is the problem addressed by the heat stress hypothesis.

 

[Billy T]

None of those links is in conflict with the heat stress hypothesis for the initial incremental boosting in brain capacity and size.

One of my six links states it is metabolically impossible to the human brain to have grown three times larger than the ape with raw food only and all of them imply that. Heat stress or not, does not over come that limitation.