Tag Archives: convergent evolution

The Subterraneans

Underground! From rabbit warrens to nuclear fallout shelters, it’s a great place to hide out. If you’re a terrestrial vertebrate, the safest place you could conceivably be is underground, where you’re protected by a temperature-stable bunker, an ocean of dirt, rocks, and roots. But it’s one thing to dig a burrow, and another to spend all your time underground, swimming through the soil. If you’re a full-time tunneler, there are really just two body types you can evolve to fit: the “mole” model, and the “earthworm” model.

Consider the difficulties of underground travel. You don’t want to be too large, or digging would be exhausting. You don’t want large eyes, which would be useless and become full of grit. You’ll need a keen sense of smell and touch, as you’re likely to be finding food by chemical and tactile signals rather than visual ones. This star-nosed mole from North America is a great example of the mole archetype: small, compact, wedge-shaped, with sealed-off eyes and ears, powerful front claws, and 22 fleshy appendages that are among the most sensitive touch receptors in the animal kingdom. Star-nosed moles are true swimmers; they breaststroke through soil, but are also quite adept at catching prey in the water. Moles are insectivores, related to that most ancient of mammals, the shrew. But thanks to the awesome power of convergent evolution, you don’t have to be related to the moles to become a mole.

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Family Reunion

Let’s talk about the first animal in the alphabet. Not only is it all alone up there at the top of the dictionary, but it’s all alone in its genetic family, a single fruit hanging from the end of a dead taxonomic branch. But although it may be alone in its immediate family, it’s got the weirdest extended family you’ve ever seen.

“A” is for Aardvark. Like the anteater, its super-thick skin protects it from insect bites as it burrows into anthills and termite mounds with powerful, clawed forearms and licks up their inhabitants with a long, sticky tongue. The resemblance to anteaters, however, is what we call “convergent evolution;” there’s no relation between the African Aardvark and its South American equivalent. In fact, there’s no relation between the aardvark and anything else. It’s the lone species in the Order Tubulidentata (“tube teeth”). To realize how lonely that is, consider that our Order is “Primates,” and imagine if humans were alone in the world without apes, monkeys, or lemurs.

A world without monkeys makes me sad.

However, “A” is also for Afrotheria. That’s the name of the Super-Order (a group below “Class” and above “Order”) to which aardvarks belong. And Afrotheria is an extraordinary example of evolutionary radiation, a single family exploding into a multitude of different forms. And my, oh my, does the aardvark have a strange extended family.

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