This fish's eyes start growing in the womb, then its own body kills them off
Astyanax mexicanus exists as two forms of the same species: a sighted river fish and a blind cave-dwelling form. Cavefish embryos begin forming eyes like their surface cousins, but the lens cells self-destruct during development, leaving the adult eyeless. Researchers see it as active natural selection against a costly organ that is useless in total darkness, not just neglect.