Question about evolution?

Question

Since the human brain is so big - sometimes causing female pelvics to break while giving birth - 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.

Jariya - If my facts are wrong then tell me. This is a question right. Just because Im an atheist that does not mean Im well versed in the theory. But I want to be hence the question

Answer 1

The birthing process is complicated moreso by our evolution to be bipedal then it is the size of the head.

The narrowing of the hips required to stand erect makes the birth canal much more difficult, and this likely occurred prior to the increased brain size we have.

If those bigger brains versus great birthing deaths resulted in a net increase in survivability, then it is by definition a positive mutation.

Answer 2

Good question. I've never heard of the pelvis actually breaking, but I think I see what you're getting at. Actually, because a wider pelvis in females allows for the birth of larger brained babies, a wider pelvis has been naturally selected in females. There are some factors that would work against a larger brain or a wider pelvis, but the benefits outweigh them. Pelvic width is a limiting factor on how large human brains have evolved to become, though.

Answer 3

You are correct: natural selection has chosen bigger and bigger brains at birth, but only at the rate it's chosen bigger and bigger pelvises. This is part of the reason a large proportion of human brain development occurs after birth.

The tendency for the human brain to increase in size is limited by the capacity of the female pelvis to accommodate a baby's head during birth. The female pelvis has also evolved to become bigger, but not quickly enough to allow human brain size to increase as quickly as it would otherwise.

Until modern obstetrics, death of the baby, the mother, or both due to obstructed labour (the head's too big for the pelvic foramen) used to be extremely common. It still is in parts of the world without access to medical or skilled midwifrey services.

Answer 4

Ok, i just read about this, so here's a serious, educated answer, but I'm not sure I can explain it as well as the author and I don't want to paraphrase it incorrectly. Read a book by the head of the human genome project, Francis Collins. He wrote a book called, "DNA: The Language of God". It explains the theories of evolution, Intelligent Design (which I didn't know the difference), natural selection, etc.
It is fairly new, but just now out in paperback. My local library has it. Anyway, I hope you enjoy it and I'll check back in a few weeks for any comments you have in case you read it.

Answer 5

If the brain were to get so large at birth to prevent live births then you would be right. Obviously you have a balance between birth success and the life success which large brains enhance.

What this has done is moved the human gestation period down to 9 months. But there is a balance there to, as you can't shorten the gestation period too much and still have successful births.

As always, you have continual tradeoffs. When it comes to evolution, there is no free lunch.

Answer 6

No, because the setbacks caused by the difficulty in giving birth are trumped by the merits of having greater intelligence and walking upright.

I added walking upright because that is part of what causes the difficulty in bearing children. Bipedalism has caused human beings' pelvises to narrow. If we were still lunging around on all fours, childbearing would be easier.

Answer 7

number 1 brain is soft tissue... it wouldn't cause that problem... someones feeding you misinformation.... and if it did occur it's because the baby is too big..... baby's are born whit the skull not fully developed as to give the head some flexibility... when you are talking natural selection.. you don't talk about the odd occurrences in one species.. you talk about the effects of the whole species.... such as 6 legged creatures are small... things with wings are small... that is a natural selection example... another example is illness... this is found in the human race actually... if you look at the trees, insects, animals.. rarely do you see epidemics or long term illnesses occurring ... things in nature rapidly are healed to avoid extinction... (extinction of an animal is caused by over hunting by humans).... humans are not respecters of nature... their religious practises interfere with evolution and nature's balance... that is why there is great epidemics and illnesses in the human race... as they cause the damage so are they receiving damage... and if humanity is unable to correct the problem with in their behaviour,,, then natural selection will cause the extinction of them all....

Answer 8

genetic mutation does not always have good consequences -
actually our brain size is slightly smaller than some prehistoric ancestor, so maybe natural selection is already at play there -
give it a few more thousands or millions of years and we`ll see !
( but wait...now with hospital, surgical procedures, big brain baby can survive...natural selection is a bit screwed up now )

Answer 9

Every design is a compromise, and in this case there are failed pregnancies because of human skull size. But Homo sapiens is 'the naked ape' and his main defence is his intelligence and social co-operation, so the requirement for problem solving and communication is paramount. Failed pregnancies are a trade-off.

But early Genesis and the rest of the Bible tells us about more important things than these. Why? _Because_ mankind needs social co-operation, and that is where God's revelation in Jesus comes in.
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Answer 10

there is greater survival value in many children being born with large brains than there is with a few people dying during birth.