This animal stole 10% of its genome from bacteria and hasn't had sex in 60 million years

Bdelloid rotifers are microscopic freshwater animals, most too small to see without a hand lens, and they have not reproduced sexually for tens of millions of years — an evolutionary strategy that should, by the standard math of biology, have driven them extinct. Without sex to reshuffle genes and keep pace with fast-evolving parasites, an asexual lineage is expected to lose the race and die out. Bdelloids didn't get the memo.

Their trick is drying out. When their pond disappears, bdelloids enter a state called anhydrobiosis, losing nearly all their body water and shutting down until moisture returns — sometimes for a very long time. In 2021, biologists reported reviving bdelloid rotifers that had been frozen in Siberian permafrost for roughly 24,000 years, and they resumed reproducing normally.

The desiccation process shatters their DNA into fragments. When the cell rehydrates and repairs itself, it occasionally stitches in stray genetic material from whatever bacteria, fungi, or plant cells happen to be nearby — a form of horizontal gene transfer that's rare among animals but routine for bdelloids. As much as 10% of a bdelloid rotifer's genome appears to have arrived this way, borrowed rather than inherited.

They escape their parasites the same way: dry out, blow away on the wind to a cleaner pond, and start over somewhere the old threats haven't followed. No sex required, and apparently no rules either.