"The human brain has been getting smaller and smaller since the Stone Age - and no one is sure why".

 

Since 20,000 years ago the human brain has gone from 1,500cc in Cro-Magnon to about 1,350cc today, losing a chunk about the size of a tennis ball.  There is no consensus why this is happening, but there are several theories:

 

1.  We are just plain getting dumber.  This is loosely based on the premise that we are "devolving" culturally and intellectually.  The movie "Idiocracy" is used as an example of this phenomenon, in which the uneducated produce more offspring than the educated. 

 

I can imagine a cultural devolution scenario - but loss of intelligence would have to be based on something more substantial than "dumb" parents.

 

2.  We are the equivalent of a domestic cow.  Just as domestic animals have developed smaller brains and are less robust than their wild form, so has man "domesticated" himself - with a similar outcome.  Now living in goups and relying on each other for safety and daily necessities man, could no longer afford to behave like a "caveman".  To preserve the cohesion of the group, the murderers and the very aggressive would be driven out or killled, and thus eliminated from the gene pool.  Being a cooperative member of the group greatly increased the chance of survival.  Having a large, robust body and an energy-hungry brain was no longer an advantage.  The wild, cunning wolf was becomiing a tail-wagging puppy.

 

Dmitri Belyaev successfully bred the aggression out of wild foxes and produced a much different animal.  After about 12 generations the foxes had developed a curly tail, floppy ears and a different coat pattern. The skeleton was smaller, more delicate, and the cranium had changed shape.  They became less noticably sexually dimorphic - and they wagged their tail, something the wild form never did.

 

3.  Although our brains have become smaller, the ratio of brain volume to body mass has always remained the same.  We have not become dumber because our brains have rewired to become more efficient.  But the reduction in brain size was not uniform throughout this period.  During times of low population density, brain size increased; during times of high population density, brain size decreased.

 

If we continue "losing our minds" at this rate, in 20,000 years we'll be back pre-human size.

 

 

 

 

 

 

 

 

Views: 96

Replies to This Discussion

Just a Hypothesis: Maybe we are loosing that portion of the brain that acts like a space heater by firing off in a seemingly random pattern. A higher population density generally correlates to better environmental controls. In general, you will notice that people from the colder climates have a larger cranium on average than people from the warmer climates.

We could also be loosing the ability to hear god.
I believe you meant "Just a theory." :-D
I wouldn't give my ideal that much credibility. I skipped step 2 and went straight to step 3 and stopped.
Good enough for a Creationist, in other words.

... or an underpants gnome.
I can think of three possible reasons off the top of my head, (no pun intended).

1. Natural selection has reduced brain size to conform to the small pelvises of the human female. We will probably find infant/maternal mortality rates have dropped at roughly the same rate over the last 20k years.
2. Perhaps we are slowly, as selection dictates, losing the parts of our brains that would have been used to figure out how to survive in a less hostile world where fewer tigers are hiding in the bushes and our answers to life's problems are built on the shoulders of those that came before.
3. You may be right. We do have a tendency to protect our weak (minded) and sacrifice our best and brightest. Altruistic behavior and intelligence seem to correlate as well. Michael is right as well. Population density is on the decline in those of traditionally colder environments and rising at explosive rates in warmer climes.

That is, as i said, off the top of my head.
2. Perhaps we are slowly, as selection dictates, losing the parts of our brains that would have been used to figure out how to survive in a less hostile world where fewer tigers are hiding in the bushes and our answers to life's problems are built on the shoulders of those that came before.

Err, I think you reversed that. I think you meant that we're losing the parts of our brain that helped us survive in a more hostile world with more tigers.
Read John Keeley's "War Before Civilization". Also Matt Ridley's "Red Queen" and "Origins of Virtue". Those tigers are not tigers, they are snakes.
I prefer to think that we are just becoming cute and cuddly.
A small female pelvis I think would be selected against. Perhaps you've seen the "earth goddess" figurines from the Stone Age, a big figured woman.

The correllation between population density and brain size has to do with having to be self-reliant when you're alone, and more reliant on others when you're in a group.
Careful with the whole "uneducated produce more offspring than the educated" thing. Just because one chooses not to get an education, or can't afford one, does not mean they are less intelligent or should I say, have the capability of becoming more intelligent. Not to mention, as one who chose to have 2 kids, I find that VERY insulting.
I DID NOT make the assertion that the "uneducated produce more offspring than the educated". That is loosely the premise of the movie "Idiocracy" to which the Discover article referred. Since very few have seen the film - including me - I had to find out what the movie was about and try to give a synopsis.

I'm sorry you misunderstood.
Not to mention, as one who chose to have 2 kids, I find that VERY insulting.

You stopped at two. That kind of 'proves' the point that he wasn't even trying to make. :-D You can get insulted by the generalization once you have number five.

Anyway, you're making the mistake that statistics absolutely say something about anyone in any of the categories represented by the statistics. They don't. They're just a way of generalizing potential causation, and you often don't even get direct causation.

If you do end up having 6 or 8 kids, it could be the result of you realizing that the religious lunatics are out-breeding us, and you're doing your part to try to balance us out. Statistics leave plenty of wiggle room for alternate causation.

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