Carl Zimmer in The Loom:
Here we see a happy, typical family of sea monkeys. Note the red bow and plump lips that indicate the female of the species, and the tall body and protective stance of the male. I assume that the father’s well-placed tail blocks some other clues to his identity. The parallels between the sea monkeys and the human family (see inset) are uncanny and surely nothing more than a coincidence.
The real life of sea monkeys (brine shrimp, or Artemia) is a pretty far cry from Ozzie and Harriet. Sea monkeys don’t live in families, for one thing. And in a lot of populations, the females have no need for males. Their eggs can develop into healthy embryos–and, eventually, adults–without the need of sperm. You can take that picture of sea monkeys and wipe Dad out.
From an evolutionary perspective, this father-free way of life has a lot going for it. Let’s say you’ve got a sexual pair of male and female shrimp in one tank, and two asexual females in the other. Let them breed for a while. Sexual species typically produce a roughly even ratio of sons and daughters. So only half of the sexual population can produce eggs, while every individual in the asexual one can. It won’t be long before the asexual population is far bigger than the sexual one. Out in the wild, this proliferation should mean that the genes for male-free reproduction should quickly dominate populations. Down with sex, in other words.