alt Hacker NewsGiven that fertility rates are currently plummeting worldwide, the principles of natural selection would dictate that humans are currently undergoing very high selection pressure for specific traits.
Basically, any genetic trait that causes people today to think "You know, I think I'm going to remain childfree" is specifically selected against, and any trait that causes people to want more children will be selected for. I'd argue that the invention of reliable birth control was that biggest change in human selective pressures in history. Evolution made sex highly pleasurable and desirable because it often resulted in passing on your genes. That's no longer true with reliable birth control, and with such a huge environmental shift natural selection will act on other avenues that cause people to have children.
True, and here's an interesting twist: as you wrote, this is mainly happening due to "I think", so it's primarily on a memetic level. Humans also pass on lots of thought/behavioral aspects to their children (memes). Therefore I'd expect that selection on the behavioral level is happening much faster than on a genetic level.
Idiocracy's "stupid genes win" likely won't happen, my theory is that selection will remove memes (behavioral/thought/cultural patterns) that cause childlessness from the meme pool much faster.
Could also well be that natural selection will rear it's ugly head again first. I previously thought that people rejecting the evolutionary theory (creationists etc) were just backwards and anti-science. But I've realized since that this is a too simple judgement. The ethical implications of evolution are dark. Humans have had a word for selection since the dawn of language - "death".
A bit sad that paraphrasing Paul Watzlawick in this context fits very well: one cannot not participate in evolution.