I grew up hearing that the main indicator of a species was that they only reproduced with one another. But Neanderthals and Humans cross bred. And they’re separate species. And in captivity Lions and Tigers can breed, but they’re obviously different species. Like I guess I’m just confused where the line gets drawn when deciding what is and isn’t a different species.
In: 50
There really is no hard line. Because evolution takes such tiny steps normally, the changes between generations makes more of a spectrum than a series of distinct steps. With the advent of genetic mapping, the line has gotten even blurrier in some ways. We can count the exact number of genetic differences between two populations, but how many is the cut off to make them two different species?
The US Endangered Species Act of 1973 doesn’t bother with defining “species” and uses the phrase “evolutionarily distinct population” to cut through that argument. Even that, though, is subject to argument, especially when money is on the line and lawyers get involved.
The definition we’re generally giving in high school these days (with an asterix) is “reproductively isolated”. The isolation can be genetic (dogs can’t mate with cats), behavioral (spring maters don’t mate with autumn maters), or geographic (I’m not swimming the Mississippi just to mate). The asterix is of course that there are exceptions even to this definition.
In short, it’s a knotty problem because we’re trying to discretely categorize things that aren’t discrete.
Latest Answers