as long as enough people are free to choose their fertility, at near enough to the real cost of fertility, with anything near the current range of genes, cultures, and other heritable influences on fertility, then in the long run we should expect to see a substantial fraction of population with an heritable inclination to double their population at least every century.Yes, that should be our default expectation, but this expectation can be undermined by another mechanism if it's powerful enough. The obvious candidate is genetic evolution becoming subservient to memetic evolution. At this stage in our species' history, it's hard to imagine more powerful evidence for the growing dominance of this new mechanism than the Demographic Transition. Still, we'd be more confident that this overthrow will be long-term if we could name other cases where the blind urge to reproduce had been enduringly subliminated to the needs of other replicating systems.
Luckily, John Maynard Smith wrote a book consisting of a list of such cases: The Major Transitions In Evolution. The most relevant transitions from his list:
- eukaryotic endosymbiosis
- biological colonialism, especially eusociality
Of course, Maynard Smith (why does he get two last names? could his kids demand four?) already listed sociocultural evolution as the most recent transition. I hope my values aren't biasing my forecast when I say I'm optimistic that this transition to memetic evolution will have a similarly enduring effect on the reproductive behaviors of the biological substrate on which it runs.
However, I doubt that the Earth will be a valid testbed for Robin's hypothesis, because I stand by my prediction in 2000 that heat pollution will in a few centuries start imposing severe and permanent pressure against growth in global standards of living.