Exaptation, Exaltation

Exaptation, Exaltation

Photograph by Spencer Lowell / Trunk Archive


Welcome to The Overview, a weekly newsletter in which Editor-in-Chief Willow Defebaugh offers a holistic look at life on Earth, seen from above.

“The art of life lies in a constant readjustment to our surroundings.”

Kakuzo Okakura

Something has become abundantly clear to me in the last week: our thresholds aren’t what they used to be, for pretty much everything. How much emotional stress we can take, how much social time we can handle, how much we can create, expose ourselves to—it has all changed since the pandemic began. Rather than lament about our newfound limitations, this week I decided to focus on what we can do with them. Nature is all about adaptation, after all. So, I turned my attention to an animal that has a lot to teach us about a change of pace: turtles.


The first thing to know about turtles is that they are an evolutionary marvel. According to an article in The Atlantic, up until a few years ago, the question of how they developed their shells had scientists stumped. Paleontologists argued that they must have come from osteoderms, the same bony scales that gave crocodiles, armadillos, and some dinosaurs their thick armor for protection. But developmental biologists disagreed—and they were right. After the discovery of an ancestor with a shell only on its belly, they came to the conclusion that turtle shells evolved from rib bones that widened and eventually came to encase their backside.


The question that came next was: why did this evolution take place? If it was for protection and survival, as many people assume, why wouldn’t these ancestors have gone the route of reptiles with osteoderms? Developing a half-shell that would inhibit both mobility and breathing would be a big risk. The answer was found in the rest of the creature’s body: namely, its muscular arms with broad claws. It turns out, the ancestors of turtles were diggers; the broadened rib cages helped to anchor the animal so that its arms could burrow into the ground and take shelter.


In evolutionary biology, exaptation refers to a trait that was evolved for one purpose and then took on another. In the case of the turtle, what was initially a tool to help it dig eventually became a suit of armor—what has come to define everything we associate with these animals. Feathers are another prime example of this: they first appeared on dinosaurs with no ability to fly, likely for warmth and mating purposes. Growth does not always go where we expect it to.


What came from that pivot in purpose is a means of protection unlike any other in the animal world. Turtles and tortoises are able to defend themselves to such a degree that other characteristics which most animals rely on for survival have become secondary. Most species of turtles have not developed advanced visual and auditory capabilities, for example; when you have a suit of armor attached to you, the need to keep an eye or ear out for predators becomes somewhat obsolete. There are benefits to having naturally strong boundaries. 


The fortresses that turtles carry with them have also allowed them to develop a unique disregard for speed, another trait that most other animals rely on for survival. Why run when you know that few things can really hurt you? In addition to their impregnable defenses, this slowness actually allows turtles and tortoises to have longer lifespans; slow-moving reptiles whose metabolisms are cold-blooded generally live longer than warm-blooded counterparts of similar sizes. Some research has even suggested that their stem cells repair themselves more frequently. 


When it comes to our own evolution, we don’t always get to know the “why” or where it’s leading us—and that’s okay. What we think we might be developing for one purpose might someday serve another. Evolution unfolds over eons. It’s okay to go slow, to move at your own pace. It’s okay to put up boundaries, to drown out the distractions. It’s okay to retract into your shell from time to time, to know your limits. What feels like a limitation now might someday be your greatest strength, and a gift for generations to come. Keep going.