David Almandsmith's picture

Your Reptilian Innards

Episode #2 of PBS’s Your Inner Fish—entitled “Your Inner Reptile”—comes complete with silly shots of people with scaly skin and snaky tongues. The slow-mo shots of leaping bikini-clad women tipped me off that the producers were mostly men. Fortunately for all of us, such silliness is brief and excellent content fills the program.

In Episode #1 of “Your Inner Fish”—cleverly titled “Your Inner Fish”—irrepressible Neil Shubin showed us that much of the anatomy and physiology of fishes and humans is very similar, but over the millions of years, a line of lobe-finned fish adapted to shallow water and mudflats. A new basic body plan emerged—the tetrapod. All terrestrial vertebrates are tetrapods; just don’t try arguing about that with a King Cobra.

Episode #2 traces the origins of other traits of the human animal—amnion, yolk sac, skin, variety in tooth morphology, hair, the 3-bone middle ear, and a larger brain. In the process, we visit Nova Scotia, the South African Karoo, and a couple of biological research labs. This time we are spared dissecting cadavers and instead get to watch a speeded-up sequence of dermestid beetle larva gorging themselves on a dead opossum. Fascinating.

Shubin presents us with several morphological developments where the scientific community is still undecided as to the most likely environmental pressures that led to them. Did the development of different-shaped teeth occur because it increased the nutrition gained from captured prey? Can the origin of hair be traced to the development of whiskers for navigating underground burrows and foraging at night? Yes, Virginia, there are controversies in evolutionary biology; but only about ‘how’ and not about ‘whether.’

We learn that both teeth and hair develop in the embryo from folds in skin tissue directed by the EDA gene. The next time you search for “hypohidrotic ectodermal dysplasia” in Wikipedia, you will find a picture of Michael Berryman whom Shubin interviewed during the episode. Michael has an EDA defect that kept his embryologic skin from folding to create teeth, hair, sweat glands, and nails. Michael has an acting career in Hollywood with roles as aliens and monsters. Again, fascinating.

“Your Inner Reptile” ends with a shopping list of human traits that have yet to be developed. I’m certain most will be covered next week in Episode #3, “Your Inner Monkey.” Since mammary glands are on the list, maybe the producers will reprise the bikini sequence.