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Friday Fun Thread for December 9, 2022

Be advised: this thread is not for serious in-depth discussion of weighty topics (we have a link for that), this thread is not for anything Culture War related. This thread is for Fun. You got jokes? Share 'em. You got silly questions? Ask 'em.

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Indeed. By the nature of evolution, closely related species blur at the edges. Interfertility remains the main criterion to distinguish species, but it's neither binary (there are many degrees of non-interfertility: won't mate > will mate but not conceive > will conceive but not carry to term > hybrids are born malformed > hybrids are healthy but sterile > hybrids are fertile but have lower fitness) nor transitive (see ring species, where A is interfertile with B and B with C, but C is not interfertile with A). Besides, most species are named on morphological or genetical grounds, because checking interfertility with their relatives would be impractical. And of course many species are exclusively asexual and do not mate at all -- just look at the mess that is bacterial taxonomy, where populations of a single "species" can be more genetically diverse than mammals and fish.