Headscratchers / Star Trek S3 E10 "Plato's Stepchildren"

• We are told that after spending time on Earth, the Platonians based their society on Plato's ideas, including his fondness for eugenics — granting them perfect health and longevity, but at the expense of resistance to infection. But later we're told that these individuals are themselves the ones who visited Greece millenia ago, so they can't very well have had a selective breeding program in that time. Maybe they experimented on themselves, similar to how Julian Bashir was augmented after birth on Star Trek: Deep Space Nine?