Exaptation Shows That Evolution Is Not Intelligent
Feathers work remarkably well for flight. Fairly rigid, yet light, with a lot of surface area to push against air molecules, they permit birds to soar to great heights. Yet scientists are now starting to realize that feathers did not originally evolve for flight. Case in point, paleontologists are now finding feathers on dinosaurs whose size rendered them incapable of leaving the ground for anything more than a leap. Turns out, the same properties that make feathers great for flying also make them wonderful for insulation.
This makes feathers a quintessential example of a process called exaptation. While it seems they originally evolved to help maintain body temperature, their form and function has since adapted for flight.
"Exaptation is rampant in evolution," writes Anastasia Thanukos of the University of California Museum of Paleontology. "Any evolutionary process that involves co-opting a trait for a new function results in an exaptation. This means that all reasonably complex traits are likely to represent a layering of exaptations and adaptations."
The earliest ancestors of turtles likely evolved shells not for protection, but to serve as platforms for burrowing underground. Legs seem neatly adapted for locomotion on land, but leg-like limbs were present in a 375-million-year-old fish known as Tiktaalik, and were likely used for propping the fish up in shallow water. There are exaptations in genes, too. A gene called Distal-less controls coloration on the wings of butterflies, but since it's found in many other animals, it likely had different jobs in the ancient past. Human symbolic thinking may even be an exaptation, argues paleoanthropologist Ian Tattersall, since the brain regions that control it evolved long before signs of language or art first appeared in the archaeological record.
"The point is to recognize that adaptations are most frequently layered on top of exaptations—that all aspects of the living world, from the spots on a butterfly’s wing to the human brain, are influenced not just by what works today but by the twists and turns of their unique evolutionary histories," Thanukos writes.
Furthermore, exaptation clearly demonstrates that evolution is not in the least bit intelligent. Rather, evolution is a messy process of mistakes, recycling, and repurposing, a collection of chance capable of creating life mesmerizingly strange and breathtakingly beautiful.