Five times Star Trek biology plots went off the rails

In a now infamous scene from a 25 year-old Star Trek:Voyager episode, Commander Chakotay and Lieutenant Tuvok beam down to a remote swamp world in search of Captain Janeway and Lieutenant Paris. Instead, the officers encounter two oversized salamanders that bear traces of the missing crew members' DNA, along with some giant salamander babies. After Chakotay stuns the adult swamp creatures and brings them back to the ship, the Doctor reverts them back to their human selves using an anti-proton treatment. Mercifully, Paris and Janeway's amphibious offspring are left behind in the morass.

Thus concludes what is widely considered one of the worst Star Trek episodes of all time. “Threshold,” which most Trek devotees have worked hard to forget (you can thank me later for reminding you), raises a host of uncomfortable questions that the show never bothered to answer. What happens to the captain's swamp spawn after the crew abandons them? Does Paris ever tell chief engineer B’Elanna, who later becomes his wife, about his amphibious offspring? How is it possible that no one ever brings up this god-awful incident ever again?

Perhaps most importantly, who the hell decided that two humans mutating into horny salamanders through an accelerated form of evolution made any sense at all as a plot point?