BIO 370Kirkpatrick & Hall, Fall 2004p. 112. Sex ratiosMost species that reproduce sexually have about equal numbers of males and femalesWhy? A species with mostly females will reproduce more rapidly. So why don’t we usually see species that are mainly female with just a few males?Is it because the sex ratio cannot evolve?No. Many species have evolved ways to make sex ratios different than 1:1Answer: When there is random mating, there is a natural selection advantage to females that produce offspring that are in the minority sexConsider a population with an excess of femalesWhat happens to a mutation that makes mothers carrying it produce only sons?That mutation ends up in males in the next generationBecause males are in the minority, they have more offspring per capita than do femalesThus the mutation speads, moving the population towards a 1:1 sex ratio
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