We may not always look it, but humans are repurposed reptiles. Believe it or not, but all of these traits reflect your inner lizard.
1. Our Yolk Sacs
When we’re embryos, a relic of our egg-laying past hangs in the womb with us—a yolk sac. Just like bird and reptile eggs, this sac provides embryos with nutrients. Yolk sacs developed about 300 million years ago when the first amphibians moved onto land. Along with the amniotic sac, it prevented their eggs from drying out.
2. Resilient Skin
It may not look like it, but our skin developed thanks to a reptilian battle with the elements. 300 million years ago, reptiles evolved a new kind of skin to deal with the dry air on land: a watertight barrier of dead skin cells, which rested atop a layer of fresh, living cells. We inherited that same layering system.
3. The Hair On Our Heads (And Elsewhere)
Sorry mammals, but reptiles beat you to the punch and grew hair first. Animals like thrinaxodon—a burrowing reptile that lived 245 million years ago—evolved whiskers to feel around in the dark. Within 20 million years, animals got hairier and hairier, and the first mammals appeared.
4. Ears and Sense of Hearing
Three bones in our middle ear help amplify sound. Amazingly, two of those bones are part of a reptile’s jaw. The fossil record indicates that over 200 million years ago, those two jawbones started receding back into ancient reptiles’ heads. Hadrocodium, a small mouse-like creature that descended from reptiles some 190 million year ago, was one of the first critters to inherit the special three-boned ear.
5. Big Brains
As late reptiles and early mammals developed whiskers and a better sense of hearing, their brains had to process more information. Because of this, their brains started to grow.
6. Our Teeth
Most modern reptiles have long, sharp, peg-shaped chompers (think crocodiles). They don’t have canines—those are strictly found in mammals. But it wasn’t always that way. The dog-like lizard gorgonopsid was one of the first ancient reptiles to flaunt long, saber-toothed canines. By the time the shrew-like tritheldonts appeared 230 million years ago, reptiles were chewing on plants and developing molar-like teeth. Teeth became more complex, setting the stage for humans—and dentists.
7. The Genes That Make Us Us
Of course, we don’t inherit reptile teeth, skin, and bones directly. We simply inherit the genes that make them possible. One gene has a lot to do with all of these transformations—EDA. EDA controls how many teeth you have, what those teeth look like, how hairy you are, and how soft and sweaty your skin is. It’s believed that mutations to EDA in ancient reptiles helped us inherit our body’s current blueprints.
Want to learn more about our reptilian past? Tune in to Your Inner Fish tonight at 10 pm Eastern/9 pm Central on PBS’s Think Wednesday lineup.