Hi Catholic Scientist
I believe you are closest to a real answer here.
The point is that the particular trait you're looking at didn't necessarily have to be the one that was being specifically selected for. Things can "go along for the ride" so to speak.
The question is what the selection is for, then to see what came along for the ride.
Another thing that I didn't see brought up yet is sexual selection. Maybe the chicks just dug the guys that exhibited traits that resulted from bigger brains.
So we look at who are considered the best choices for mates: rock stars or nobel prize winners? Entertainers vs thinkers?
Long hair, large breasts, large penises, youthful appearances are all "abnormal" compared to other primates thus they are evidence of selection pressures for those traits. These traits have no survival advantage to speak of, and may even result in lower survival rates on their own. This leaves sexual selection and the competition for mates and reproductive success.
Rahvin
Message 15: But there's one possibility that involves an intellectual arms race without limit.
Competition with each other.
The smarter we get, the smarter the competition, and so even smarter individuals still have a selection advantage. It's an evolutionary spiral. Each increment is small, but the selective pressure is never actually overcome because there are always more humans to compete with.
This is one part of sexual selection: males compete with males for domination in order to have more mating opportunities. This does account for the sexual dimorphism in size (personally I believe this is becoming less, but that is my thoughts on the matter).
nwr
Message 17: Start paying more attention to the Republican candidates for US President. You might change your mind on whether the brain is overpowered.
Indeed. These people are definitely NOT the sharpest tacks in the box, yet they appeal to many people as leader types.
This again shows that intelligence is NOT what is being selected for in mates\leaders.
Catholice Scientist
Message 7: The point is that the particular trait you're looking at didn't necessarily have to be the one that was being specifically selected for. Things can "go along for the ride" so to speak.
Message 18: But you're still trying to find a need to fill for a positive selective pressure towards bigger brains. The point was that there might not even be that need there in the first place.
The size of the brain came along for the ride: what was being selected for that benefited from increased brain size\power?
Straggler
Message 19: The human brain uses a lot of energy. It requires a lot of feeding.
Without any positive selection pressure it seems unlikely that such an "expensive" organ would evolve purely as a side product of other factors in the way I think you are suggesting.
That might be how it started out. But some sort of selection for bigger and bigger brains does seem to be required to explain the result we have ended up with.
Sexual selection seems a viable candidate. Big brains are sexy.
Again: look at sexual selection in operation in our society today -- who are the sexiest women\ men? Compare them to who are the most intelligent women\men.
Catholic Scientist
Message 27: The same goes for the peacock tail... they don't need it, it resulted from other selective pressures. That's what I'm talking about.
Bingo. When you see a trait that has evolved to the point where it can go no further without overly impacting the survival rate of the carriers, when you see a trait that is not distributed in a bell curve, but a skewed curve pushed up against one end, where further development is not beneficial to the species, then you are looking at a run-away feedback loop selection --
Fisherian Runaway Sexual Selection:
quote:
Fisherian runaway is a model of sexual selection, first proposed by R.A. Fisher in 1915,[1] and expanded upon in his 1930 book The Genetical Theory of Natural Selection,[2] that suggests an explanation for sexual selection of traits that do not obviously increase fitness of survival, based upon a positive feedback "runaway" mechanism.
Fisher's explanation is that selection of such traits is a result of sexual preference; that members of the opposite sex find a trait desirable. This preference makes the trait advantageous, which in a circular fashion makes having a preference for the trait advantageous.
The process is termed "runaway" because over time, it would facilitate the development of greater preference and more pronounced traits, until the costs of producing the trait balance the reproductive benefit of possessing it.
By way of example, the peacock's tail requires a great deal of energy to grow and maintain, it reduces the bird's agility, and it may increase the animal's visibility to predators. Yet it has evolved, indicating that birds with longer tails have some advantage.
Also see
Sexual Selection, Stasis, Runaway Selection, Dimorphism, & Human Evolution for additional thoughts I have on this topic.
Fisherian Runaway Sexual Selection explains:
- large brains
- apparent bareness
- long head hair
- year round large breasts (while fertile)
- large penises
- etc
It is apparent to me that what is selected for in mates is creativity and youth, rather than intelligence, and that brain size came along for the ride.
Sex made us what we are.
Enjoy.
added by edit:
Tangle
Message 37: A related puzzle, or maybe more evidence of how valuable our brains are, is the fact that having such a large brain is a very distinct reproductive disadvantage. The babies brain is so large that it doesn't fit easily in the birth canal and without medical intervention a very large number of mothers and babies simply die in childbirth.
Then the baby has to be born whilst it's still immature because if it carried on growing to the physical maturity of most mammals at birth, the head would be so large that it simply couldn't emerge from the mother. This means that the mother has to invest many years of full time nurturing in order to get her offspring to the point were it can survive on its own.
Add extended development outside the womb as a means for even larger brains to evolve The extended childhood is also longer than any other primate, with a human child not able to fend for itself until ~9 years old, just a few years short of sexual maturity (and hence the neotenty is also linked).
Enjoy.
Edited by Zen Deist, : added end comments
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