The Amazon molly is an all-female fish species that reproduces clonally. It steals sperm from related species to trigger egg development but discards the paternal DNA — every offspring is a genetic copy of the mother. Muller's ratchet predicts this should be fatal within ~10,000 years: without sexual recombination, harmful mutations accumulate irreversibly until the genome collapses.
The Amazon molly has thrived for at least 100,000 years — ten times longer than theory permits.
The through-claim: the hybrid's internal mismatch is the repair mechanism. The Amazon molly's genome contains two divergent chromosome sets inherited from its original interspecies hybridization event. Gene conversion — a copy-and-paste DNA repair process where small stretches of code are copied from one chromosome to another — operates between these mismatched sets. Because the chromosomes differ, gene conversion can overwrite a harmful mutation on one chromosome with the functional version from the other.
In a normal clonal species with identical chromosomes, gene conversion copies broken code onto broken code — it can't repair anything because both copies are the same. The Amazon molly's genomic discord — two different parental genomes that don't quite match — provides the substrate diversity that makes repair possible. The flaw (being a hybrid with mismatched chromosomes) is the feature (having a template for error correction).
Muller's ratchet assumed that asexual reproduction eliminates the recombination needed to purge mutations. But gene conversion between divergent chromosome sets acts as a substitute for recombination without requiring sex. The ratchet doesn't click because the teeth don't catch — there's always a clean copy somewhere in the genome to paste from.