I agree that contraception makes a big difference. There are also general cultural differences here. In Sweden it is becoming increasingly common to have children without getting married, apparently in the expectation that the children will be raised by the community of friends even when the parents split up. I have two cousins once removed born to unmarried parents, and indeed their parents are no longer together. There is no social oppobrium. This does not contradict your point; in Sweden even children with no parents will not lead lives of poverty, though I don’t know about loneliness.

Have you read Jeff Hawkins’ On Intelligence? He lays out a theory of how intelligence works in humans that’s pretty plausible. The book’s worth reading even if you don’t buy it, because there is still a lot of interesting stuff there. His group has recently released a free-beer software library (surely patented, non-commercial use only) that implements the algorithm he believes the neocortex runs.

Speaking of singular events:

I’ve been struck lately by the huge significance of the invention of contraception. Before contraception, a lot of the societal strictures we laugh at now really did make sense: a pregnancy outside marriage, if brought to term, was quite likely to lead to a life of poverty and loneliness. Given the the strength of physical attraction, there was a real argument for parents and society exercising strict control over children and young adults.

How many of our values and mores descend from the need to prevent people from having sex outside marriage, and prevent them from having sex too often within marriage? Does the list include some we don’t recognize as directly related to sex? By greatly reducing the associated risks, those values become safe to abandon, even if doing so does dismay the older generations.

I’m especially interested in seeing which of the old-fashioned romantic ideals turn out to rest on needs that remain in force: I don’t expect the generation of children born in this decade to be completely free of scruples, even by our standards, regarding how they treat their SOs.