Further to the Steve Jones theory about the end of human evolution, there's a post by PZ Myers at Panda's Thumb on yet another way in which he may well be proved wrong – the Caesarean section:
While Steve Jones might think human evolution has stopped, I have to say that that is impossible. If human technology removes a selective constraint, that doesn't stop evolution — it just opens up a new degree of freedom and allows change to carry us in a novel direction.
One interesting potential example is the availability of relatively safe Cesarean sections. Babies have very big heads that squeeze with only great difficulty through a relatively narrow pelvis, so the relationship in size between head diameter and the diameter of the pelvic opening has been a limitation on human evolution. We know this had to be a factor in our evolution: the average newborn mammal has a cranial capacity that is roughly 50% of the adult size, chimpanzee babies have heads about 40% of the adult size, but human babies have crania that are only 23% of what they will be in adults. While our brains have gotten larger over evolutionary time, they have not gotten proportionally larger in utero, because large-headed babies increase the difficulty of labor and cause increased mortality in childbirth. If childbirth could bypass the pelvic bottleneck, that would allow for fetal heads to grow larger without increasing the risk of killing mother and/or child.
And childbirth is a risky proposition for women; 529,000 die every year from this natural process (although only about 1% of those deaths occur in places where women have access to good, modern medical facilities — hooray for modern medicine). About 8% of those deaths occur from obstructed labor, where the fetus is unable to proceed through the birth canal for various reasons, and these are the kinds of birth problems that can be circumvented by C-sections. In practice, teaching health care workers how to carry out emergency C-sections has been tested in regions in Africa, where it has actually worked well at reducing maternal mortality.
This is the subject of an article by Joseph Walsh in the American Biology Teacher, which suggests that C-sections will have an effect on human evolution.
"Nothing in biology makes sense except in the light of evolution." This was the title of an essay by geneticist Theodosius Dobzhansky writing in 1973. Many causes have been given for the increased Cesarean section rate in developed countries, but biologic evolution has not been one of them. The C-section rate will continue to rise, because the ability to perform a safe C-section has liberated human childbirth from natural selection directed against too small a maternal pelvis and too large a fetal head. Babies will get bigger and pelves will get smaller because there is nothing to prevent it.
Myers is unconvinced by the evidence to date, but, as he says, it's a tantalising idea:
Even as a purely theoretical exercise, though, what it does say is that it is obvious that human culture cannot end human evolution…all it can do is shape the direction in which it can occur.
Mick Hartley 
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