[gumby]

> Same for lions, btw, although I don't know about their sex' birthrates.

If you don't know the rate how can you say it's true?

By definition there is some sort of distribution of male/female cubs and there is presumably some sort of distribution of pack sizes. But apart from the victorian-inspired documentaries that talk about juvenile male ronins being chased from the pack I don't really know the dynamics, and I doubt anyone but a specialized community does. Where I live in Palo Alto the distribution of lone mountain lions that show up in town seems, anecdotally, to be predominantly female.

Humans are a good example: slightly more males are born but within the range of about 20-50 years of age, the sex ratio is 1:1. Humans have been basically* monogamous throughout recorded history and for whatever reasons that might be it would select for this birth ratio wouldn't it.

* Sure, there are plenty (well, a few percent) of kids whose father is not the male in a given hetero "couple" but it's the couple phenomenon itself that matters here.