Re: Shrinking brains in evolution
- From: Kermit <unrestrained_hand@xxxxxxxxxxx>
- Date: 14 May 2007 07:38:46 -0700
On May 13, 3:06 pm, Mike <mat...@xxxxxxxxxxx> wrote:
On May 13, 10:08 am, dkomo <dkomo...@xxxxxxxxxxx> wrote:
In _Evolving Brains_, John Allman mentions that early modern humans had
brains that averaged 1450 grams, whereas the average for contemporary
humans is about 1300 grams. He opines that this is a result of the
"domestication" of humans. The development of agriculture and
domestication of animals as sources of food and clothing have served as
major buffers against environmental variability.
Reduction in brain size and neuron number have been observed in many
domestic animals relative to their wild counterparts. Dogs have brains
that are about three quarters the size of the brains of wolves of
comparable body size. Humans have assumed the responsibility for
providing food and shelter for dogs, and thus the dog's necessity for
maintaining a larger brain is decreased. Large brains are also very
energy intensive, and so there is a selective advantage in making them
smaller.
Another example comes from the comparison of the retinas of European
wild cats and domestic cats. Domestic cats have 40% fewer retinal
ganglion cells, which relay the input of the retinas to the brain. This
major loss of neurons might be produced by programmed cell death in
development and linked to domestication.
--dk...@xxxxxxxx
It seems to me that modern computers are both much more powerful
and much smaller than computers in the 1960s. More efficient design.
Evolution does not "design" except if we use the word
figuratively, but accomplished the same result. Besides the fact that
the brain is a greedy organ (i.e. consumes 26% of your oxygen and 29%
of your glucose), humans have immense difficulties with childbirth
compared to other animals due to the large size of the baby's head.
Clearly there would have been strong evolutionary pressure to evolve
brains as good or better that were smaller. It would be foolish to
suppose that there is any linear correlation between brain size and
intelligence, particular when we compare ancient and modern human
specimens.
Here's an animal with a brain the size of a pecan making a tool and
using it:
http://news.nationalgeographic.com/news/2002/08/0808_020808_crow.html
Birds are under *very strong selective pressure to keep their brains
lightweight. Humans have a selective pressure for smaller brains to
save on energy, too, altho I think your point about the dangers of
human childbirth is much more significant. We pretty much solved the
food problem by 100,000 years ago.
Also, we may have lost some brain mass in areas that have nothing
directly to do with what we think of as intelligence. Look at the cat
example losing retinal ganglions. Perhaps we lost some kinesthetic
intelligence or something else. My wife and I have speculated on how
we may have bred ourselves to be more domestic over the last 13,000
years or so. We have selected out those who have poor impulse control.
Folks who are more social probably have more reproductive advantage
than their paleolithic ancestors did. Our immune system may have
improved, at least as far as communicable diseases are concerned.
But it wouldn't surprise me if we are dumber than paleolithic humans.
How well would they have done ignoring reality for some social
construct?
Kermit
.
- References:
- Shrinking brains in evolution
- From: dkomo
- Re: Shrinking brains in evolution
- From: Mike
- Shrinking brains in evolution
- Prev by Date: Re: Majority of scientists in US believe in god
- Next by Date: Re: Abiogenesis
- Previous by thread: Re: Shrinking brains in evolution
- Next by thread: Re: Okimoto vents some hot air and Prof Chiel offers unsupported claims about the predictability of IC
- Index(es):
Relevant Pages
|
