In a clumsy effort to seduce her, I was trying to explain the evolutionary advantages of sexual reproduction to a female friend the other day, one of which I said was introducing an element of genetic competition into the process. She wanted to know why, if two sexes are needed to create genetic competiton, why aren鈥檛 there three, four or a million sexes to create even more competition? So why are there only two?
Tim Rowland, Bristol, UK