As you may know, one of the factors influencing the human choice of a mate is (shh!) B.O. Sure, so what's new?

It appears that:

(1) certain genes play a role in the characteristics of body odour by causing chemical interactions with skin bacteria

(2) we are attracted by body odours produced by those genetically dissimilar to ourselves

Fine, so what's the problem?

One problem may be the contraceptive pill. It may disrupt a woman's instinctive attraction to a genetically different mate.

Result:

(1) fertility impairment

(2) risk of miscarriage

(3) weakened immunity in offspring

(4) increased likelihood of breakdown in connubial relationship.

See http://royalsociety.org/news.asp?id=7937

"Time is what prevents everything from happening at once" - John Wheeler