If anyone else is surprised by that claim, turns out it's not quite true (in a blurry way): [The variety between eye types] has led to the dogma that eyes have

If anyone else is surprised by that claim, turns out it's not quite true (in a blurry way): [The variety between eye types] has led to the dogma that eyes have evolved in all animal phyla 40 to 60 times independently (Salvini-Plawen and Mayr 1961). However, recent genetic experiments cast serious doubts on this notion and argue strongly in favor of a monophyletic origin of the various eye types followed by divergent, parallel, and convergent evolution. https://academic.oup.com/jhered/article/96/3/171/2187545/New-Perspectives-on-Eye-Development-and-the https://academic.oup.com/jhered/article/96/3/171/2187545/New... Even at a wider structural level, there is enough common ancestry to put a serious damper on the idea that it evolved independently 20 times. It's more like a single origin for major photosensitive proteins, and one origin per major eye type. That's not to say it never happens, notably, there's a behavioral trait in ants (seed dispersal) that appears to have evolved independently at least 100 times. Sometimes everything is set up to favor convergent evolution with dozens or more independent occurrences, but that probably wasn't the case with the eye.