Apparently, I really did kind of pay attention during undergrad bio class.

A lot of the biochem has definitely dissipated, but I do still think about genetics from time to time, probably because it was the emphasis to my major.

The biological species concept has been a mainstay for the modern definition of species.

The biological species concept defines a species as members of populations that actually or potentially interbreed in nature, not according to similarity of appearance. Although appearance is helpful in identifying species, it does not define species.

However, it still has a lot of caveats:

• We already pointed out two of the difficulties with the biological species concept: what do you do with asexual organisms, and what do you do with organisms that occasionally form hybrids with one another?

• What is meant by “potentially interbreeding?” If a population of frogs were divided by a freeway, as shown below, that prevented the two groups of frogs from interbreeding, should we designate them as separate species? Probably not—but how distantly separated do they have to be before we draw the line?

• Ring species are species with a geographic distribution that forms a ring and overlaps at the ends. The many subspecies of Ensatina salamanders in California exhibit subtle morphological and genetic differences all along their range. They all interbreed with their immediate neighbors with one exception: where the extreme ends of the range overlap in Southern California, E. klauberi and E. eschscholtzii do not interbreed. So where do we mark the point of speciation?

• Chronospecies are different stages in the same evolving lineage that existed at different points in time. Obviously, chronospecies present a problem for the biological species concept—for example, it is not really possible (or very meaningful!) to figure out whether a trilobite living 300 million years ago would have interbred with its ancestor living 310 million years ago.

There do seem like there are a lot of distinct species that are able to breed with other distinct species and yield viable offspring.

On Facebook, people have been posting articles about coywolves.

• Coywolf: New coyote-wolf hybrid sees explosion in numbers • 2015 Nov 1 • Zachary Davies Boren • Independent
• Greater than the sum of its parts • It is rare for a new animal species to emerge in front of scientists’ eyes. But this seems to be happening in eastern North America • 2015 Oct 31 • The Economist

While most people think hybrid offspring of different species are generally less vigorous than their parents (and usually sterile like mules), coywolves seem to be doing better than wolves in certain environments.