Every Amazon Molly Is Female. The Name Tracks.

Meet the Amazon molly Poecilia formosa, a small freshwater fish that has been cloning itself (no male DNA required) for around 100,000 years. According to a study in Nature, the animal's genome looks surprisingly healthy.

When animals reproduce sexually, recombination shuffles genes and helps populations purge damaging mutations over time. Asexual species skip that safety valve entirely. In theory, bad mutations accumulate faster and faster, and limited genetic variety makes adaptation harder. This phenomenon is sometimes called Muller's ratchet, and it's generally regarded as a death sentence for species that reproduce by cloning. The Amazon molly has been ignoring that sentence for longer than Homo sapiens have existed.

The fish appears to use a DNA self-repair process called gene conversion, where one copy of a gene overwrites another. Using long-read sequencing, researchers documented this process at a detailed genetic level for the first time. The mechanism transfers small stretches of genetic code between chromosomes, erasing unfavorable mutations and sometimes spreading beneficial ones, keeping natural selection in play.

Back in 2018, researchers first mapped the Amazon molly's full genome expecting to find the genetic damage left behind by millennia of cloning. Instead the DNA looked healthy, similar to what scientists would expect in a sexually reproducing species. It took new sequencing technology to explain why.

Because similar repair mechanisms are involved in cancer and genetic disease, the Amazon molly has become an unlikely but valuable model for understanding human health.

It turns out asexuality isn't a dead end. The molly likely has more to teach us.

Read the full story at Popular Mechanics, March 11, 2026

Hot Take: Reading more of the research, the fish still dupes males of related species into releasing sperm to trigger egg development, but then uses none of their DNA. Honestly, respect.