# Evolution: Skull, Brain & Jaw Size



## RobynC (Jun 10, 2011)

I really should know this shit in more detail but needless to say I do know the following: As we evolved into humans a number of things happened to our bodies but the most important thing happened to our brains.

As our jaws shrunk in size, our skulls got bigger allowing a bigger brain to fit within them making us a great deal smarter than our predecessors. Unfortunately as our jaws shrank, the amount of force we could put down with biting became less but the ability to make tools ultimately got around that problem.

I'm not sure if the brain maxed out when our jaws shrunk to accomodate 32-teeth in them, or continued expanding after that point. Anybody have an answer?


_BTW: Interestingly the male brain at it's biggest (I mention male brains because they have always been bigger than a woman's brain - something which seems tied to scale) was 3.5 pounds and is now 3.0 to 3.05. Assuming scaling was always the same this would have made the primitive female brain 3.2131 to 3.2-2/3 pounds.

Some have claimed that it's the result of the fact that we have sort of "domesticated ourselves" while others claim that we've somehow made our brains more efficient for the same size. Truthfully I wouldn't be surprised if both arguments are correct in various ways._


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## OldManRivers (Mar 22, 2012)

The organization and complexity of the brain are of as much influence as size. The only thing that can be said is the end result, and some of the intermediate forms along the way.


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## He's a Superhero! (May 1, 2013)

It should be noted that brain size doesn't necessarily correlate with level of intelligence.


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## wuliheron (Sep 5, 2011)

With the exception of brain size, physiologically we are no different today than cavemen were millions of years ago. With half our brain power **** erectus evolved the unique hunting style of literally running their prey into the dirt from heat exhaustion. Humans have almost no fur, an unheard of 200 sweat glands, are incredibly efficient runners, and the only animals on earth than run all day long many of the hottest places on earth. To this day a few primitive tribes still run their prey into the dirt, which takes the better part of a day usually.


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## Purrfessor (Jul 30, 2013)

Instead of our brains growing bigger we developed those fissures to increase the surface area. Also I believe intelligence is most accurately recorded with the brain-to-body ratio. The bigger the better. Humans haven't developed solely for intelligence. We also have a very handy body, which will probably stay with most of the human race forever because we move a lot for fun and whatnot. It's not all about the brain.


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## ApostateAbe (Aug 8, 2013)

He's a Superhero! said:


> It should be noted that brain size doesn't necessarily correlate with level of intelligence.


Brain size matters. Recent studies of brain size and intelligence among humans report correlation coefficients between 0.3 and 0.6. There was a lot of denial about it in the science and in the public (i.e. Gould's _Mismeasure of Man_) before the existence of brain imaging technology.


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## He's a Superhero! (May 1, 2013)

ApostateAbe said:


> Brain size matters. Recent studies of brain size and intelligence among humans report correlation coefficients between 0.3 and 0.6. There was a lot of denial about it in the science and in the public (i.e. Gould's _Mismeasure of Man_) before the existence of brain imaging technology.


I said that brain size doesn't _necessarily_ correlate with level of intelligence. Some very intelligent animals have small brains.


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## ApostateAbe (Aug 8, 2013)

He's a Superhero! said:


> I said that brain size doesn't _necessarily_ correlate with level of intelligence. Some very intelligent animals have small brains.


OK, thanks for clearing that up. The correlation exists in the whole animal kingdom, too. Since correlation allows for exceptions, it would be more accurate to say that greater brain size doesn't necessarily _indicate_ greater intelligence. The correlation absolutely exists regardless of the exceptions.


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## He's a Superhero! (May 1, 2013)

ApostateAbe said:


> OK, thanks for clearing that up. The correlation exists in the whole animal kingdom, too. Since correlation allows for exceptions, it would be more accurate to say that greater brain size doesn't necessarily _indicate_ greater intelligence. The correlation absolutely exists regardless of the exceptions.


Women's brains are smaller than men's brains, and yet they have the same intelligence.


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## monemi (Jun 24, 2013)

wuliheron said:


> With the exception of brain size, physiologically we are no different today than cavemen were millions of years ago. With half our brain power **** erectus evolved the unique hunting style of literally running their prey into the dirt from heat exhaustion. Humans have almost no fur, an unheard of 200 sweat glands, are incredibly efficient runners, and the only animals on earth than run all day long many of the hottest places on earth. To this day a few primitive tribes still run their prey into the dirt, which takes the better part of a day usually.


Off topic, but I found it interesting that the area in sports where you see the least significant difference between men and women is endurance. Women probably aren't about to beat men for best world time for marathons. But it's one of the fairer competitions between the sexes. I would think this makes sense in terms of evolution. 

I shamed some guys that were training for a marathon when I was pregnant. Even 5 months pregnant, my time on my 5km run was still better than theirs. At least I gave them a heads up that they needed to step up their game. Running is one of the few exercises you can keep up all 9 months of pregnancy if you're in good health. I'm absolutely sure we were born to run. I feel it.


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## ApostateAbe (Aug 8, 2013)

He's a Superhero! said:


> Women's brains are smaller than men's brains, and yet they have the same intelligence.


Yes, no disagreement.


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## RobynC (Jun 10, 2011)

Because of the nature of the replies, they generally follow along two topics which I've divided by topic and the replies

Subject I: Size of Brain and Organization

@_OldManRivers_ @_He's a Superhero!_ @_wuliheron_ @_Stelliferous_

A.) That's why I put that whole BTW thing at the bottom
B.) I'm mostly interested in change in dimensions from an anatomical standpoint (I know the wiring changed quite a lot)


Subject 2: Brain Size and Efficiency

@_ApostateAbe_

1.) Why was there denial about it in the scientific community?
2.) How much of a percentage do those coefficients have on overall dimensions

@_He's a Superhero!_

There are exceptions to the rule but the fact of the matter is that among certain species there's generally a ratio of brain-mass to body-mass.

This is why, by the way, the reason that men have bigger brains than women and yet intellectual capacity are very similar.

Male brain average: 3.00 to 3.05 pounds
Female brain average: 2.80 pounds (91.8033% to 93.3333% the mass)

Now how big is an average man?: 5'9" to 5'11"
How big is an average woman: 5'3.7" to 5'5" (89.7183% to 94.2029% the size)

The small irregularities seem to account for the fact that 

1.) Men have a bigger upper torso than women for the same height

2.) Men generally have bigger hands and feet and a lot of nerves are required to control these areas

3.) Mens and Women's brains do have some differences in some areas as to the exact amount of white and grey matter


There are also several other responses which might not neatly fit in so I'll address them here…

@_wuliheron_



> With half our brain power **** erectus evolved the unique hunting style of literally running their prey into the dirt from heat exhaustion. Humans have almost no fur, an unheard of 200 sweat glands, are incredibly efficient runners, and the only animals on earth than run all day long many of the hottest places on earth. To this day a few primitive tribes still run their prey into the dirt, which takes the better part of a day usually.


Correct, many animals can run quickly -- way faster than us -- in quick bursts but however humans can run for unbelievably long distances without stopping (There are some creatures which can sprint some serious distances however: Bears can go full throttle for about a half hour as can wolves; some humans can run more than half a day at an albeit slower speed but you do that and you'll either exhaust most prey or you'll find something else to kill instead)

This is actually why humans have longer legs than most other animals -- it's not for speed, it's for cruising: Even to this day, barring a congenital defect, if you trained most people to run long distances (particularly from a young age), they could generally run marathons.

@_monemi_

Correct. In fact the wider hips we have makes it harder to run faster and requires more power for the same speed. This is also why women have stronger legs than men for the same weight (more power required for the same result)

Interestingly though jumping performance is less affected than sprinting performance and there are women who can do as good as men in that regard while still being unable to run as quick (like me -- though I can outrun quite a number of men too)

The primary characteristic required for long-range cruising is long-legs which both men and women have, women have longer legs actually and while the wider hips tend to hinder things a little, the extra length works out on a cruise and nearly evens things out.

I routinely run 10 miles every day _(either a morning run, or the treadmill which is boring as shit but I do it anyway)_, still takes about an hour to do it.


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## ApostateAbe (Aug 8, 2013)

RobynC said:


> Because of the nature of the replies, they generally follow along two topics which I've divided by topic and the replies
> Subject 2: Brain Size and Efficiency
> 
> @_ApostateAbe_
> ...


The perceived correlation between brain size and intelligence was used to justify racism and sexism. So popular authors like Stephen J Gould and Carl Sagan preached against it like it was a pseudoscience.

"How much of a percentage do those coefficients have on overall dimensions?" Do you mean like brain size to body size ratio? Don't know.


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## RobynC (Jun 10, 2011)

@ApostateAbe

I meant brain size to intelligence...


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## ApostateAbe (Aug 8, 2013)

RobynC said:


> @ApostateAbe
> 
> I meant brain size to intelligence...


I still don't understand the question. Can you rephrase it?


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## RobynC (Jun 10, 2011)

@ApostateAbe

The coeficient thing...


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## ApostateAbe (Aug 8, 2013)

RobynC said:


> @ApostateAbe
> 
> The coeficient thing...


The correlation coefficients fall between 0.3 and 0.6. That means 30% to 60% of the way between no correlation (random scatter) and perfect correlation (straight line) of the two variables: brain size (presumably volume) and IQ.


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## RobynC (Jun 10, 2011)

So brain size has a 30%-60% relation to intelligence?


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## ApostateAbe (Aug 8, 2013)

RobynC said:


> So brain size has a 30%-60% relation to intelligence?


Yeah, that way of expressing it isn't too bad.


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## RobynC (Jun 10, 2011)

If correlation was direct though it would vary 100%
with size right?


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## RobynC (Jun 10, 2011)

Regardless, back to the fossil record... my primary interest

First: At what point did our brains start getting larger and our jaws start getting smaller
Second: At what point did our jaws remain large enough to carry 32 teeth in them?
Third: At what point did our brain reach maximum mass
Fourth: When did our brian reach current mass?


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## monemi (Jun 24, 2013)

RobynC said:


> Regardless, back to the fossil record... my primary interest
> 
> First: At what point did our brains start getting larger and our jaws start getting smaller
> Second: At what point did our jaws remain large enough to carry 32 teeth in them?


I only had two wisdom teeth. My dentist said I have small jaws. The two wisdom teeth I did have were a tiny, strangely shape and pointed horizontally/backwards with shallow roots. They were rubbing against the soft tissues in my mouth. The rest of my teeth are naturally straight. My half sister never had any wisdom teeth and neither did my Dad. Is it just me or do less and less people have wisdom teeth? 

I think our jaw sizes are still changing. Cooked meat isn't as difficult to chew as raw meat. We don't need large jaws.


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## RobynC (Jun 10, 2011)

@monemi

You mean you only had two teeth that grew in, or just two formed?


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## ApostateAbe (Aug 8, 2013)

RobynC said:


> If correlation was direct though it would vary 100%
> with size right?


I don't know what you mean by, "direct," but I think you probably understand the idea.


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## ApostateAbe (Aug 8, 2013)

RobynC said:


> Regardless, back to the fossil record... my primary interest
> 
> First: At what point did our brains start getting larger and our jaws start getting smaller
> Second: At what point did our jaws remain large enough to carry 32 teeth in them?
> ...


Here is a timeline of increasing cranium size in our ancestry:










The trend has not slowed down. Darwin hypothesized that large human brain size and human intelligence is due to sexual selection of powerful males by females, and that hasn't stopped, either.

I can't answer the question about the teeth.


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## Swordsman of Mana (Jan 7, 2011)

RobynC said:


> I really should know this shit in more detail but needless to say I do know the following: As we evolved into humans a number of things happened to our bodies but the most important thing happened to our brains.
> As our jaws shrunk in size, our skulls got bigger allowing a bigger brain to fit within them making us a great deal smarter than our predecessors. Unfortunately as our jaws shrank, the amount of force we could put down with biting became less but the ability to make tools ultimately got around that problem.
> I'm not sure if the brain maxed out when our jaws shrunk to accomodate 32-teeth in them, or continued expanding after that point. Anybody have an answer?
> _BTW: Interestingly the male brain at it's biggest (I mention male brains because they have always been bigger than a woman's brain - something which seems tied to scale) was 3.5 pounds and is now 3.0 to 3.05. Assuming scaling was always the same this would have made the primitive female brain 3.2131 to 3.2-2/3 pounds.
> Some have claimed that it's the result of the fact that we have sort of "domesticated ourselves" while others claim that we've somehow made our brains more efficient for the same size. Truthfully I wouldn't be surprised if both arguments are correct in various ways._


diet
in contrast to our ape ancestors (from circa 7 million years ago), we eat
- more meat
- less cellulose vegetation
- cooked food (which acts as a sort of pre-digestion process, both making the food easier to chew and more nutrient efficient)

the resulting effect was
- smaller jaw 
- smaller gut (cuz we need less digestion power)
- more room freed up for the brain case to expand


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## Swordsman of Mana (Jan 7, 2011)

ApostateAbe said:


> Here is a timeline of increasing cranium size in our ancestry:
> 
> 
> 
> ...


this is wrong on a few levels
1) neanderthals had a larger average cranial capacity than modern humans (1450cc)

2) more intelligent does not always equal "better". 
- according to this study the distribution of sexual activity and intelligence is more of a bell curve (and it makes sense of if you think about it. Vin Diesel and Bradley Cooper probably get way more sex than Bill Gates or Steven Hawking). 
- there are other disadvantages to extremely high intelligence such as over analyzing and hesitance to take action (just ask any Enneagram 5 or 6w5). this is why Donald Trump makes a lot more money than Einstein or Aristotle ever did (though this is a problematic assumption even in itself, as income is often _negatively_ correlated with birthrates in modern times). 
- more brain size (and, by loose correlation, more intelligence) requires more caloric energy to function. 

3) human brain size stopped decreasing around 50,000 years ago and has since decreased to around 1350cc on average (source: The Human Species: an Introduction to Biological Anthropology, Relethford 2010)

obviously, I'm not saying that intelligence isn't useful or that we should all turn back into club swinging **** erectus (**** erectae? lol), but, like any biological advantage, is has a diminishing marginal utility after a certain point.


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## monemi (Jun 24, 2013)

RobynC said:


> @_monemi_
> 
> You mean you only had two teeth that grew in, or just two formed?


I had two oddly shaped wisdom teeth that grew in. My dentist said usually what would happen is the wisdom teeth would crowd the rest of the teeth in the jaw, because there isn't enough space for them. Instead, they shifted to a very odd position where the gum meets ligament.


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## OldManRivers (Mar 22, 2012)

monemi said:


> Off topic, but I found it interesting that the area in sports where you see the least significant difference between men and women is endurance. Women probably aren't about to beat men for best world time for marathons. But it's one of the fairer competitions between the sexes. I would think this makes sense in terms of evolution.
> 
> I shamed some guys that were training for a marathon when I was pregnant. Even 5 months pregnant, my time on my 5km run was still better than theirs. At least I gave them a heads up that they needed to step up their game. Running is one of the few exercises you can keep up all 9 months of pregnancy if you're in good health. I'm absolutely sure we were born to run. I feel it.


Another way to see that is the people (women, in particular: the fight or flight decision would favor the smaller female burdened by an unborn child who could run and run and. . .) that could run would eat more and be eaten less.


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## RobynC (Jun 10, 2011)

*Swordsman of Mana*

What I'm wondering is when our brain reached it's maximum size, were our jaws already shrunk below the capacity to fit all it's teeth in there?


*Monemi*

I know there's a gene that prevents them all from coming in, I didn't know only two could come in


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## Brynja (Oct 13, 2013)

RobynC said:


> *Swordsman of Mana*
> 
> What I'm wondering is when our brain reached it's maximum size, were our jaws already shrunk below the capacity to fit all it's teeth in there?
> 
> ...



Ooo  I only grew the bottom two as well. I didnt know there was a gene for any of this at all actually...


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## monemi (Jun 24, 2013)

RobynC said:


> *Swordsman of Mana*
> 
> What I'm wondering is when our brain reached it's maximum size, were our jaws already shrunk below the capacity to fit all it's teeth in there?
> 
> ...





Brynja said:


> Ooo I only grew the bottom two as well. I didnt know there was a gene for any of this at all actually...


I didn't know anything about a gene to prevent wisdom teeth from coming in. Any idea how old that gene is?


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## saksham (Aug 27, 2013)

well i really believe our brains are devolving..... whats actually evolving is our stupidness :shocked:


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## Zero11 (Feb 7, 2010)

He's a Superhero! said:


> It should be noted that brain size doesn't necessarily correlate with level of intelligence.


Or simply put it that way that if the brain is too big your "controller" isn´t able to handle it anymore which means being dumb.


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## Obscure (May 20, 2013)

Does bigger car meen more suitable/comfortable or faster? >.>


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## He's a Superhero! (May 1, 2013)

saksham said:


> well i really believe our brains are devolving..... whats actually evolving is our stupidness :shocked:


I think we all get to choose if we do stupid things or not (at least to a degree). My advice is don't feel the need to always follow the crowd!


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## Manny (Oct 15, 2013)

Interesting fact:
Hominid brain size began increasing at an exponential ratio once we began to eat meat.
Our large brains easily accommodated to the high levels of protein in meat.


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## RobynC (Jun 10, 2011)

Where would I find more info?


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## LadyO.W.BernieBro (Sep 4, 2010)

l never had Wisdom teeth either.

My face and jaw are about the same size as when l was 13.

l've had weird delays like this for a lot of things, though. Could they show up later :shocked:


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## Arya (Oct 17, 2012)

RobynC said:


> @_monemi_
> 
> Correct. In fact the wider hips we have makes it harder to run faster and requires more power for the same speed. This is also why women have stronger legs than men for the same weight (more power required for the same result)
> 
> ...


I should be a good runner judging from this, but I'm not.  I have long legs, and narrow hips, but I can't run without pain. I have stupid pronating feet. Has anyone shown how feet have evolved?


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## Up and Away (Mar 5, 2011)

I think a strain of us used to have bigger brains actually, but lacked something else crucial for survival.


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