Question about evolution?

Question

Since the human brain is so big - sometimes causing female pelvics to break - wouldn`t natural selection work against humans evolving to have bigger brains?

BTW - I`m an atheist that does not deny that evolution is a fact. This question is merely a gap in my understanding - it is not some creationists attempt to prove the theory wrong.

Answer 1

Not if it was more reproductively advantageous than the deaths of women who could not give such live birth. Reproductive advantage is all in evolutionary processes, so, to make that omelet, many eggs have been broken over the time span of many organisms.

Look to our slow development. Would it not be more advantageous to develop much faster and avoid that long and mostly helpless phase? No, as reproductive success is greatly increased by the strategy of intellectual development we were selected for.

Answer 2

A lot has been sacrificed evolutionarily speaking for the big brains and thus big heads humans have in relation to body size. It must have been a huge advantage to have these big brains or the things you mention that work against big brains would have prevented them from coming about.

In addition to the difficulty of birthing, there is the long period of time required for a human baby to be able to even walk around on it's own, much less take care of itself. Human babies are born prematurely compared to other primates and mammals. The brain develops a lot more after birth in humans than it does in other organisms. The prolonged infancy is another price paid for the big brains.

Answer 3

It would not work against *any* growth of brain size, it would only be selected against once the baby's head started getting too big for a safe birth.

But there's an alternate adaptation that has also occurred, and that is *earlier* birth ... the baby being born earlier in its gestation. This is one reason why the human baby is *unusually* helpless (as compared to other placental mammals).

Another result of early birth is something called 'neoteny' ... where the adult of our species retains some of the juvenile characteristics. This may have something to do with the evolution of hairlessness.

Answer 4

Natural selection does not work to pick only the best traits. For each good trait, there is a cost. The cost of having large brains is a large head. The benefit far outweighs the cost.
Oh, and Darwin was actually a Christian his entire life...take a class on evolutionary history (not just reading some pro creationism website). Remember that people can write whatever they want to on the internet, that doesn't mean it is true.

Answer 5

Our big heads are a burden but they have value as well. They cause us to use much energy and we have to haul it around but it does a lot of good too. With our big heads we learn how to acquire food, mates, etc. With every feature we have evolved, it is sized on the ideal for the particular niche. For example, our bones are just strong enough to make breaking not likely. If they were stronger, they would be too heavy. Everything has an optimal size or shape that may get modified with changing environments. Charles Darwin was a Christian who figured out how animals evolve. He didn't become one IMO as the next answer suggests. It doesn't mean he believed everything in Genesis

Answer 6

Yes.
But natural selection doesn't work in only one direction (or even two directions; you have to stop thinking one or two dimensionally). There are selection pressures that also selected for larger brains.

It's a trade-off, but also evolutionarily compensated by the development of a larger pelvic girdle (in women).

Answer 7

the size of the human brain is caused by the number of neurons needed to the body activities.

Answer 8

if you want answers, become a christian. Charles darwin, a famous person for his evolution theories, became a christian at the end of his studies because he knew his theory was wrong.