Agriculture and Speciation
Artificial selection is well known in evolution classrooms as an example of the powers of selection and descent with modification. Indeed, domestication of wild species has led to loads of tasty, cuddly, and weird plants and animals. Does domestication play a role in speciation? Are domesticated plants and animals their own species?
Ever hear of Great Danes, toy poodles, broccoli, or cabbage plants? If you’ve never heard of any of these things before, we encourage you to learn about them. Go ahead. We’ll wait.
When we talked about cabbage and broccoli before, we mentioned that they are plants of the same species (Brassica oleracea). What we didn’t mention was that they also share this species umbrella with kale, Brussels sprouts, collards, and kohlrabi.
The story for the dogs is similar, except that Great Danes and toy poodles aren’t just the same species; they're the same subspecies (Canis lupus familiaris)—a subspecies of the grey wolf. That's right. Underneath all its cuddliness, your pet Malti-poo is just a wolf with thousands of years of artificial selection working to increase its cuteness and decrease its aggressiveness. As different as a Malti-poo is from a wolf, or a Brussels sprout from a kale plant, they don't qualify for separate species status.
The reason they don't qualify as species is that they can usually still interbreed with their wild ancestors. This doesn't mean that they're not well on their way to becoming their own species some day, just that the thousands of years of artificial selection haven’t done the trick yet. If they're not distinct species, what are they? This is where we enter the breeder's vocabulary of cultivars, races, breeds, and varieties. These are different ways of acknowledging and classifying the differences among organisms that belong to the same species. How convenient.
Before giving up completely on the idea of artificial speciation, there is some evidence for it in sheep and fruit flies, an odd couple to say the least. Jack Lemmon and Walter Matthau odd. Domestic sheep can no longer interbreed with their wild ancestor, Ovis orientalis. Laboratory experiments with fruit flies have shown that it's possible to induce reproductive isolation between lab populations grown in different habitat types and food substrates. From this, scientists have determined that there is evidence that it's possible, but artificial speciation hasn't happened yet. For the time being, evidence is in short supply, but even a little bit of evidence counts as evidence. Give it a few million years and see what happens.