Sperm count is unlikely to affect the population growth anyway, what we need is to get people out of poverty and proper family planning with access to proper birth control. Then we can "control" the population.
Don't forget educating women, which tends to result in fewer children per household.
I am concerned, though, that the temporary lull in overpopulation will be broken by belief systems that encourage large families; by definition, those with a genetic or memetic instinct to have many children will out-populate those without that instinct. (I have a soft spot for the Mormons, but they come to mind here.)
Memes aren't strictly inheritable in the same way that genes are.
For example, it is completely plausible to advance the argument that children in large families decide to have fewer offspring due to their own childhood experiences. I'm not saying that this is definitively the case or that I have any evidence for it, but it is just as plausible as the conjecture that a propensity for a large number of offspring is perfectly inheritable.
Even if memes are not genetically heritable, they are still transmissible, and therefore still subject to selection pressures. And the more children these families have, the broader the attack surface for large-family beliefs to infect the next generation.
Moreover, I would suggest that genetics do influence tendencies for adopting some memes over others, especially as regarding the instinct to spread genetic material, which is very ancient. I can't cite any scientific support for this idea, but the likelihood seems very strong.
Because it's demonstrably successful at curbing population growth rate? Because during periods of the most aggressive enforcement of the one-child policy, China had its highest growth rate in recent history, 2-2.5x that of the US?
And now, during its period of least aggressive enforcement, but with a rapid pace of industrialization and wealth injection, the growth rate has fallen dramatically?
Or perhaps we want to look at Japan, which without forced abortions, property confiscation, and brutal acts of repression have managed to achieve a negative growth rate?
No matter which way you slice the data, the trend is clear: industrialization, wealth, and stability decrease growth rates, and do so far better than any number of guns and Bibles you can point at people.
> Because during periods of the most aggressive enforcement of the one-child policy, China had its highest growth rate in recent history, 2-2.5x that of the US?
The fact that China would think to enforce such a policy should give one pause.
I don't think that policy is so great. People don't have children just because they can, we need to educate people about children and population growth. My aunt and uncle have an adopted daughter from China, she was abandoned as a result of the one child policy: the policy didn't stop her from being born, but it stopped her from having her biological family.
That does lead to other problems, like putting a strain on the welfare system of countries when there suddenly is a huge decrease in the number of people that support those who have retired.
Look at Japan where there are fewer and fewer supporting more and more. It is kinda working for now but what will happen in 20 years? Who knows.
My guess? We'll gradually shift back into larger households, with several generations living under one roof. Not that bad, when you come to think of it.
Sperm count is unlikely to affect the population growth anyway, what we need is to get people out of poverty and proper family planning with access to proper birth control. Then we can "control" the population.