This Microbe Isn’t Either Male or Female, It Has Seven Options to Choose Between

This little protozoa has seven different “mating types”

Tetrahymena thermophila. Photo: R. Robinson

The sexual identities of the teeny little protozoan Tetrahymena thermophila are full of diversity (and not in a Kinsey Scale kind of way). The diversity of thermophila arises not in their range of sexual preferences, but in their genders, for which they have seven options.

In fact, the little protozoa are actually pretty laissez-faire when it comes to sexual preference: each of the seven different genders can reproduce with the six others. They only cannot have babies with others of their own gender (which says nothing of love.)

Scientists, says Nature, have known about the gender variability of thermophila since the 1930s, but they never really understand how a specific protozoa came to have a single gender or “mating type.” But now, says Popular Science, research suggests that the decision is, basically, random. The mating type of the parents doesn’t matter:

“It’s completely random, as if they had a roulette wheel with six numbers and wherever the marble ends up is what they get. By chance, they may have the same mating type as the parents –– but it’s only by chance,” explains Eduardo Orias, a UCSD professor emeritus who has studied T. thermophila for more than 50 years. “It’s a fascinating system.”

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