That's a good point, the amount of variation changes over time. I'd be extremely surprised if the current amount somehow fell all the way to zero though. There

That's a good point, the amount of variation changes over time. I'd be extremely surprised if the current amount somehow fell all the way to zero though. There's apparently some speculation (according to the Wikipedia article on the Flynn effect at least) that the Flynn effect is due to non-genetic factors, in which case the underlying genetic trends are being obscured. There's a claim that genotypic IQ could be decreasing but we're not seeing that reflected effect in phenotypes due to environment improvements (which probably won't continue forever).