Aristotle spent serious time on this and concluded eels spontaneously generated from mud, that's not a knock on him, you genuinely cannot find reproductive organs in a wild eel because they don't develop until the final migration, it took satellite tagging in 2018 to actually confirm what was happening. A 2,300 year old mystery closed by a GPS tracker is a good reminder that some problems just had to wait for the right instrument
I remember being fascinated by animals as a kid and the mystery of where eels went was one of the big unsolved puzzles I remember hearing about.
Much more recently I heard on QI about how medieval people, not knowing about migration, believed, through a lot of leaps, that it was ok to eat barnacle geese at lent. Worth investigating if you are curious :)
Fascinating how certain animals have evolved with complex migration patterns to breeding grounds. And unfortunate that 95% of the population has already collapsed.
Makes me wonder what the world was like before this last great extinction.
tl;dr Eels have a long lifecycle with several stages. They do not develop sexual organs until late in their life, when they migrate back to the Saragossa Sea. This meant earlier autopsies of eels revealed no sexual organs, even though scientists could provoke them with hormone therapy. So, a team lead by Jose Azevedo tagged female eels in the Azores in 2018, and tracked them via satellite [0].
I sometimes think about the selection pressures that lead to complex life cycles, like fig wasps. I find myself thinking about it naively, like one existed and the other grew into the niche. But, realistically, everything is changing (slowly) all the time. I just notice it for, say, influenza because their cycle time is so short.
Much more recently I heard on QI about how medieval people, not knowing about migration, believed, through a lot of leaps, that it was ok to eat barnacle geese at lent. Worth investigating if you are curious :)
Medieval Science was Baffled by Birds - CuriousCabinet123
https://youtu.be/vgFj-MMTqIc
Makes me wonder what the world was like before this last great extinction.
[0] https://www.nature.com/articles/s41598-022-19248-8
I sometimes think about the selection pressures that lead to complex life cycles, like fig wasps. I find myself thinking about it naively, like one existed and the other grew into the niche. But, realistically, everything is changing (slowly) all the time. I just notice it for, say, influenza because their cycle time is so short.