Can a sex imbalance raise intelligence?
As a result of son preference and selective abortions, the sex ratio at birth (the number of males for each female) in some Asian countries is significantly skewed. This has been the case for a number of decades now, and may continue for a few more. As a reference, an example from China and India: among their 15- to 24-year-olds, there are, respectively, 1.14 and 1.13 males per female.
Aside from the problems that this sex imbalance creates in these societies, a curious consequence of it might be a slight rise in their intelligence over time. Women tend to select men whose financial prospects appear more promising, which prospects correlate with intelligence in the modern world in no small degree — let alone that intelligence by itself is usually appealing in a potential partner. Thus more children are likely to be born from the more intelligent men (the less intelligent ones are the ones less likely to marry), and since intelligence is highly heritable, the average intelligence of each generation emerging from this imbalance may then quite plausibly be a bit higher than that of the preceding one.