One thing that over a generation or two that could have a significant impact is the effect of Caesarean sections, where according to the BBC
http://www.bbc.com/news/science-environment-38210837The regular use of Caesarean sections is having an impact on human evolution, say scientists......
Researchers estimate cases where the baby cannot fit down the birth canal have increased from 30 in 1,000 in the 1960s to 36 in 1,000 births today.
Historically, these genes would not have been passed from mother to child as both would have died in labour.
Researchers in Austria say the trend is likely to continue....
This means that (those surviving) could expect about 4% of mothers to die in child birth from this problem. This is a high number, which with other complications, could make increasing the population a deadly risk factor.