Let's talk about sex...ratios (evolution that is)

Ruchira Paul sent me an email asking me to clarify this exposition of how gene selectionism can explain 50:50 sex ratios. First, I would like to second the author of the original post's injunction to read Richard Dawkins' The Selfish Gene, it is a masterpiece of scientific exposition. For many people an encounter with the The Selfish Gene is a K-T scale event, the world is changed after the encounter. That being said, it surely isn't the last word. A friend of mine mentioned how she noted that Dawkins heaps scorn on Amotz Zahavi's Handicap Principle, but a generation later this model has gained a modest level of acceptance. The Selfish Gene was written in 1975, and though it is a classic, it is not timeless in all its particulars. With that caution and exhortation out of the way let us move on to sex ratios. We know mechanistically that ...