Why the gender ratio is 1:1

Well, I’m heading off to a wedding in the family, so I figure if I don’t get a chance to write anything else for the weekend, I may as well leave you with knowledge of Fisher’s principle. Ever wondered why the gender ratio is 1:1 rather than, say, many more females than males? Read that and you’ll know why. Isn’t science grand?

2 Responses to “Why the gender ratio is 1:1”

  1. drinian Says:

    Sadly, makes much sense.

    I’m too lazy to make a joke about gender ratios of harem anime.

  2. Gregory Maxwell Says:

    Last night Kat and I saw a Virginia possum in the yard. Tonight we were discussing their peculiar marsupial breeding habbits and their short lifespans and Kat posed the question, “I wonder if there are more female than male?” Remembering Fisher’s principle, I responded “No. It’s 1:1, it’s always 1:1” and sent her to the Wikipedia article.

    She was quick to point out that the Wikipedia article mentions that the 1:1 ratio doesn’t hold up all the time. The cited paper “Hamilton, W.D. 1967 Extraordinary sex ratios Science 156: 477-488” is utterly fascinating. Basically, if the sex-selecting factor is itself sex-linked then Fisher’s principle does not necessarily hold, although it appears that such a situation is anti-adaptive and the balancing mutations usually occur. Because of this some cases of hybrids (breading of near-related species) can produce highly tilted sex ratios, due to the absence of the balancing mutations.

    There appears to be class of behaviors where an imbalanced ratio is stable: Under conditions of exclusive incest combined with some very specific genetic sex selection mechanisms a mostly female population is stable. The paper has a couple of examples of this in several types of parasitic arthropods that live in wasps and figs. Though I found myself wondering if a species propagates itself exclusively via incest really counts as sexual reproduction.

    (Ultimately Kat agreed that my generalization that “it’s always 1:1” was pretty much correct.)