By Olivia Judson in The New York Times

Ciliates like the paramecium have very unusual sex, a fact often unmentioned in high school biology class.

When it comes to sex and reproduction, mammals are ultra-orthodox and, frankly, rather dull. Individuals are either male or female, no one changes sex and there are never more than two sexes in a species. No mammal reproduces asexually — by budding off a small piece of itself, say, or by splitting down the middle and growing a new individual from each half. Nope: among mammals, offspring are always produced by sex. That is, an egg fuses with a sperm to produce a child that is genetically distinct from both parents.

But things can get much hairier. Take ciliates — which get my vote for Life-form of The Month: February.

Most ciliates are single-celled organisms covered with tiny hair-like structures known as cilia — which is Latin for eyelashes. The cilia are used for a variety of activities, including swimming and feeding. Some ciliates even use them to scuttle across surfaces.

Behind the cilia, however, ciliates are a diverse and ancient group. Their lineage split off from the one that we evolved from more than a billion years ago; their closest relations are the apicomplexans (a group of single-celled parasites that includes Plasmodium, the bug that causes malaria) and the dinoflagellates (which I profiled in January).

Ciliates live in all kinds of places, from the guts of cockroaches to the waters around Antarctica, and they have a range of lifestyles. Some are filter feeders, sieving particles of food from the water like microscopic blue whales. Others are active predators, harpooning their prey (usually bacteria, or other ciliates) and killing them with poisons.

And if you’re a fact jock, you’ll like this detail. Almost all organisms on the planet read their DNA with the same language, so that if you put a jellyfish gene into a pig, you get exactly the same product in both organisms. Ciliates, however, don’t play strictly by the rules: they have repeatedly evolved small variations on the normal way of reading genes. (They also, mysteriously, have rather a lot of genes: some have as many as 30,000, which is several thousand more than we have.)

[Read the full article at

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