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Old 03-01-2021, 05:25 PM   #14
Socratic Monologue
Originally Posted by WebSlave View Post
Has the definition for "species" changed too?

Used to be that the definition implied that only members of the same species could interbreed with each other. But heck, breeding snakes threw that definition right out the window when people successfully bred specimens from completely different genera together.
The short answer is 'yes'.

There are quite a few definitions of 'species'. Linnaeus determined species by morphotype -- basically, animals that look the same (this is kind of what hobbyists like to do, too). An 'evolutionary species' is one that maintains a line because it can't or doesn't mix with other species. A 'genetic species' (what you're referring to, I think) is a line of animals that cannot breed with another because of genetic incompatibility.

'Cladistic species' -- an idea that is driving most current taxonomic updates -- determines a species to be an animal group that has branched off genetically from a (genetically) nearby species.

Cladistics is the idea that living things should be taxonomically ordered based on shared ancestry (rather than what they look like or who they breed with) -- a 'clade' is a group of animals with a shared ancestor. It is overturning a lot of commonly held ideas, such as the idea that reptiles and birds are distinct groups -- on a cladistic analysis, birds and reptiles are both in the clade Reptilia, because there isn't a point in evolutionary history where birds and all the things we commonly call reptiles (that is, snakes, lizards, crocs, turtles and tuatara) split into two groups. Birds are actually more closely related to turtles and crocs than any of those three are to snakes, lizards and tuatara.

Neither is there any cladistic classification that matches up with 'herps' (reptiles+amphibians), since reptiles share a more recent common ancestor with mammals than they do with amphibians.

Any real biologists can feel free to correct me on the details. I had the basic outline of this in my head, but I had to look up some things I wasn't sure I was describing accurately.