Baby boys born small for their gestational age have a greater chance of infertility as adults than those born at an average weight, research suggests.
One of the things we can observe is that in times of dearth the male/female ratio at birth changes. The ratio at conception we think doesn’t change, but there’s at least limited ability for the womb to “choose” what to allow to come to fruition.
The standard explanation for the change in the usual 106 boys to 100 girls (or so) at birth is that a runty male is no good in the gaining grandkids stakes. Those stakes being the only ones anyone is playing for. Pretty much any woman who is fertile can, if she desires, have a child or more. This is not true of less favoured males.
Hmm, OK. So, in times of famine why bother to try to have a male child? Spontaneously abort, try again next month.
Not sure if this changes that explanation or is in addition to it. For it would lead to the same sorta result. Underweight males are infertile – or more likely to be – rather than just ill-favoured in pursuit of a mate. We’d get to the same end result of any selection process in those times of dearth, wouldn’t we?