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As male chickens are killed after birth in mass farming. Will being male become a negative evolutionary trait, that is to say will females become more likely as male death is more likely.

Joshua Farrell
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  • Also a follow up, does the chicken industry use selective breeding to increase the chance of females? – Joshua Farrell Jan 25 '20 at 23:17
  • What do you mean by "the chance of females". I suppose you are still talking about sex-ratio. In all cases, please ask your follow-up questions on a separate post. Note that chicken are a GSD (Genetic Sex Determination) species. Just like other birds, they have a ZW sex chromosome system. There is therefore not much that can be done to bias the sex-ratio. Related post: Do males of all sexual species have Y chromosomes? – Remi.b Jan 30 '20 at 04:19

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Any chick has a mother and a father. Hence, the contribution to the gene pool of the following generation comes at 50% from males and at 50% from females. As a result there is no selection for biasing the sex-ratio among its offsprings. The variance in reproductive success might be higher among males than among females but that does not matter for the sex-ratio.

This is known as Fisher's principle. In the terms of W.D. Hamilton (Extraordinary sex ratios), copy-pasted from wikipedia:

[..] given the condition that males and females cost equal amounts to produce:

  • Suppose male births are less common than female.
  • A newborn male then has better mating prospects than a newborn female, and therefore can expect to have more offspring.
  • Therefore parents genetically disposed to produce males tend to have more than average numbers of grandchildren born to them.
  • Therefore the genes for male-producing tendencies spread, and male births become more common.
  • As the 1:1 sex ratio is approached, the advantage associated with producing males dies away.
  • The same reasoning holds if females are substituted for males throughout. Therefore 1:1 is the equilibrium ratio.

To my knowledge, only kin/group selection can yield a sex-ratio different from 1:1 to be an ESS.

Remi.b
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  • Let's assume all male chicks are killed, and all eggs are fertilised by some other population of males, not influenced by the farmed hens. Say for example a certain chicken (a female in this case) is more likely to produce females by some genetic mutation. Then chicks of said hen will also have a greater chance of producing females. This hen will have more female chicks than the average hen. Hence over time the sex-ratio tends towards females. – Joshua Farrell Jan 31 '20 at 06:52