To better understand the evolution of sex, a number of biologists are looking to the exceptions to the rule. Populations of sexual animals may be less prone to going extinct because they can adapt to more niches. Or perhaps the rarity of asexual animals is the result of evolution playing out not in short-term competitions, but over vast stretches of time. Perhaps that’s a cost too great to balance the advantage of giving up fathers. That’s a lot of extra DNA to build when a cell divides–which requires a lot of phosphorus and other ingredients. Very often, when an asexual lineage emerges, it gains an extra set of chromosomes. There may be different explanations for different cases. Defenses against ever-evolving parasites might be especially important. Maybe sex lets adaptations evolve faster, because mothers and fathers can combine genes into new combinations. Scientists have given this question a lot of thought, and they’ve come up with some possible answers that they’ve been testing in recent years. Sex must have a powerful advantage that overcomes its disadvantage–what the late biologist John Maynard Smith dubbed the two-fold cost of sex. Down with sex, in other words.īut this has only occurred in only about one in every ten thousand species of animals. Out in the wild, this proliferation should mean that the genes for male-free reproduction should quickly dominate populations. It won’t be long before the asexual population is far bigger than the sexual one. So only half of the sexual population can produce eggs, while every individual in the asexual one can.

Sexual species typically produce a roughly even ratio of sons and daughters. Let’s say you’ve got a sexual pair of male and female shrimp in one tank, and two asexual females in the other. You can take that picture of sea monkeys and wipe Dad out.įrom an evolutionary perspective, this father-free way of life has a lot going for it. Their eggs can develop into healthy embryos–and, eventually, adults–without the need of sperm. And in a lot of populations, the females have no need for males. Sea monkeys don’t live in families, for one thing. The real life of sea monkeys (brine shrimp, or Artemia) is a pretty far cry from Ozzie and Harriet.

Seamonkey picture