I am not a biologist, so I can guarantee that I really have no clue what I’m talking about. Needless to say, I’ll charge ahead stubbornly anyway.
I was listening to Radiolab a couple weeks ago, and they did an interesting bit on conservation in the Galapagos — in particular, half the episode was about an invasive parasite that is endangering three species of finches on one of the islands, and the resulting interbreeding of those finches in the face of annihilation. Now, as I’ve mentioned, I’m not a biologist, but I very distinctly recall that in my 6th grade biology class a species was defined as a set of individuals who can create fertile offspring — a donkey and a horse are not the same species, because when they mate, they produce mules, which are infertile; a chihuahua and a St. Bernard, however, produce a batch of fertile puppies (it helps if the mom is the St. Bernard), because they are the same species. So how was it that three separate species were interbreeding and producing fertile offspring?
This question has actually crossed my mind a number of times before, since basically every other week we discover that we’re not actually X% Cro-Magnon man, we’re actually some weird hybridization of (X-1)% Cro-Magnon and (Y+1)% Neanderthal.
And with extinct species it’s particularly difficult to tell anything about species and speciation, since species are constantly evolving and changing, and if you look at, let’s say, the slice of 2 MILLION years during which we know that T. Rex existed, we only have about 50 specimens to determine what constitutes the species, while in the last two million years, the genus Homo has gone from this:
Now tell me that with 50 specimens in a two-million-year period you’re going to have any clue what constitutes natural variation within a given species (keep in mind that, at least technically, Justin Bieber can produce fertile offspring with Anne Hathaway or Jennifer Lawrence or whomever you take to be the height of evolutionary perfection) and two completely separate species, and it’s not hard to see that the concept of species is just totally 100% man-made bunk.
I mean, it’s not entirely useless — I was trained as an engineer, and I still work a lot with models, and as understandable, simplified representations of the real world, models are incredibly useful. The species model gives biologists a shared and meaningful framework for all sorts of things — again, not a biologist, but I’d assume it’s much easier to have a formal classification system so that you can discover that Huge Green Turtle with Domed Shell and Green Spot is resilient to drought, but Huge Green Turtle with Domed Shell and Red Spot is susceptible to drought, and then when drought hits The Island With Huge Green Turtles with Domed Shells, you know how to react and which to worry about. And sure, maybe they can breed, but they don’t, and their gene pool stays separate in practice, so hey — good model, or whatever.
So I was kind of taken aback listening to that episode of Radiolab to hear a biologist just freak right the F out about the finches interbreeding (see around 15:45-17:30 in the episode). The hosts present the species concept as “a biological rule” specifying which individuals will or will not mate, and then treat the breaking of that rule as this crazy thing that’s never happened before, when in reality we think that this “rule” is just a model — a simplification that proves true in most cases, but not all — and that that model has broken at every stage in our own evolutionary process. All I could think was, “Here’s this biologist who ought to know better going crazy because her model broke, like she’d never seen it before or realized it could, in the face of countless known instances where exactly that has happened.”
I ran this little incident by my friend (who happens to be a biologist), and she …
- had already heard about the Galapagos finches and thought it was a pretty big deal, and…
- told me why it was such a big deal.
It turns out that, yes, the species model is just a model, and it is acknowledged as such, and in fact there are many species models, and the “species problem” (essentially, what actually constitutes a species) has been around in some form or another since before Darwin even made it to the Galapagos. Ernst Mayr explored the definition of species in Systematics and the Origin of Species, eventually settling more-or-less on the “textbook” definition given above. More generally, though, the various species models may also take into account physical characteristics (…with Green Spot vs. … with Red Spot, or in the case of the finches in question, song pitch and size) or statistical clustering of genetic characteristics, where the lines may be a bit fuzzy, but generally you’ll see two fairly distinct populations when comparing the genes of some large sample of members of two different species, and you can say with some certainty given the genetic characteristics of a new sample whether it’s one or the other.
I’m about to do something that I very, very rarely do, so cherish it: I admit that I was wrong. Well, with the caveat that the hosts sorta bungled the presentation. They presented it as though the biologist in question was amazed at the breakdown in the model, when upon re-listening, I realize that what she was actually presenting as amazing was not the fact that previously-thought-to-be-different species were mating, but the creation of a new species in a way that biologists expected had happened and could and would happen, but had never seen happen before in vertebrates, and that this speciation was occurring at a wicked fast rate. The end result of this process would be a new statistical clustering of genetic characteristics, representing a group of finches sharing physical similarities that largely chooses to mate among that cluster, fitting pretty nicely into any of the various species models presented.
And that actually is pretty cool — because now that they’ve found a new finch, they can correct one of the greatest social injustices of our times by naming it Atticus.