> But anyone who thinks that this effect will last for billions, millions, or even thousands of years has failed to understand evolution.
Oh really? Evolution selects for survival, period. (Actually, survival selects for certain kinds of evolution.) Where is it written that survival implies over-population.
No. Evolution selects for genes that manage to leave lots of descendants. This is a local optimization that is not the same as long-term survival. In fact there are lots of examples of species going down evolutionary dead ends where eventually they get wiped out.
Thanks to the miracle of exponential growth, a successful trait that is possessed by a small fraction of the population will spread like a cancer until it dominates the population.
In the case of humans, any trait that leads to lots of kids despite economic pressures to have few of them is going to be evolutionarily successful. And it will be successful in a surprisingly short time. To take a simple model, suppose that we have a recessive allele that is 1% of the gene pool. (So 1.99% of the population carries the recessive, but only 0.01% of the population expresses it.) Suppose that people without it just replace themselves, while people with it expressed have twice as many kids. At first the trait will be utterly invisible. But in under 100 generations it will completely dominate the population. That is only a few thousand years.
> Evolution selects for genes that manage to leave lots of descendants.
Nope.
Survival selects for genes that have enough descendants. One way to have "enough" is "lots", but it doesn't necessarily work and isn't necessary.
> In the case of humans, any trait that leads to lots of kids despite economic pressures to have few of them is going to be evolutionarily successful.
Nope - lots of kids is neither necessary nor sufficient. The key metric is "do your kids have kids, rinse and repeat." Too many kids can break that, as can too few.
All else being equal, in an environment like our own where survival is easy, generally the more kids the merrier.
Modern economics and birth control have created pressures against reproducing that we have never faced in our evolutionary history. Our species has not yet evolved a response to it. Once we have evolved a response to it, I would predict exponential growth rate until we exhaust available resources.
This may not happen in 10 generations or 20. But in 1000 generations, our species will have adapted and reached a crisis.
The only way I see of "evolving a response to it" is selecting for baby-crazed women who are basically addicted to the hormonal changes of childbirth and rearing. Men would already be happy to impregnate women as much as possible, if they didn't have to stick around or pay child support.
And you think that selection process is not going on?
Anyways there are other possible responses. There is a strong correlation between being religious and having lots of kids. Therefore genes that incline one towards being religious are positively correlated with kids.
Another is a trait of failing to worry about future consequences. (Now you'll really be thinking about Idiocracy.)
Complex traits like these are part nurture and part nature. But to the extent that they are nature, there is evolutionary pressure for them to spread.
Evolution selects for genes that manage to leave lots of descendants.
Actually, it selects for different things in different environments.
r-strategists, that leave as much offspring as possible starting as early in life as possible survive well in unstable environments. Heaps of offspring is being produce, but only a small percentage survive to reproduce.
In stable, predictable environments, however, K-strategists thrive. They leave less offspring, but care for them long enough and good enough so that most of the offspring survive. Think species like humans, whales, elephants etc.
No, evolution always selects for the same goal. There are different strategies for attaining that goal, and in different environments those strategies work out differently. But the goal is always the same - do you many generations later have lots of descendants with the gene?
Oh really? Evolution selects for survival, period. (Actually, survival selects for certain kinds of evolution.) Where is it written that survival implies over-population.