[autosharp]

E.g. most chickens (about 2/3) that come out of their egg are male. But a flock only allows maybe 1 adult male for every 5 females, with the surplus murdered by other chickens. So almost all male chickens are superfluous in that sense. It is still selective pressure which makes chickens have 'too many' males, because apparently those chickens/flocks have created more of themselves.

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

[rybosworld]

Birth sex ratio of chickens is naturally 1:1.

You can do weird things with temperature to affect those birth rates, but the ratio will not reach as high as 2:1 as far as I know.

[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.