The limiting of birth rates can last for a very long time as long as you stay at replacement rates. I don’t think “obvious evolutionary reasons” apply to humans any more, it’s not likely another species will outcompete us by breeding faster.
In the “long-long run”, given ad hoc reproductive patterns, yeah, I’d expect evolution to ratchet average human fertility higher & higher until much of humanity slammed into the Malthusian limit, at which point “when people have more food they have more kids” would become true.
Nonetheless, it isn’t true today, it’s unlikely to be true for the next few centuries unless WWIII kicks off, and may never come to pass (humanity might snuff itself out of existence before we go Malthusian, or the threat of Malthusian Assured Destruction might compel humanity to enforce involuntary fertility limits). So here in 2014 I rate the idea incontrovertibly false.
… don’t they? (in the long run)
No, they don’t—look at contemporary Western countries and their birth rates.
Oh yes I know that, I just meant in the long-long run. This voluntary limiting of birth rates can’t last for obvious evolutionary reasons.
I have no idea about the “long-long” run :-)
The limiting of birth rates can last for a very long time as long as you stay at replacement rates. I don’t think “obvious evolutionary reasons” apply to humans any more, it’s not likely another species will outcompete us by breeding faster.
Any genes that make people defect by having more children are going to be (and are currently being) positively selected.
Besides, reducing birthrates to replacement isn’t anything near a universal phenomenon, see the Mormons and Amish.
It’s got nothing to do with another species out-competing us—competition between humans is more than enough.
This observation should be true throughout the history of the human race, and yet the birth rates in the developed countries did fall off the cliff...
And animals don’t breed well in captivity.
Until they do.
This happened barely half a generational cycle ago. Give evolution time.
So what’s your prediction for what will happen when?
In the “long-long run”, given ad hoc reproductive patterns, yeah, I’d expect evolution to ratchet average human fertility higher & higher until much of humanity slammed into the Malthusian limit, at which point “when people have more food they have more kids” would become true.
Nonetheless, it isn’t true today, it’s unlikely to be true for the next few centuries unless WWIII kicks off, and may never come to pass (humanity might snuff itself out of existence before we go Malthusian, or the threat of Malthusian Assured Destruction might compel humanity to enforce involuntary fertility limits). So here in 2014 I rate the idea incontrovertibly false.