The recent publishing of the green sea turtle genome brought back memories of my first encounter with baby sea turtles, and one of the most fun and astonishing examples of hardwired behavior I know of. I had the good fortune to travel to Heron Island in the Great Barrier Reef during my undergraduate days. We were there in March and April, the Down-Under Fall, when the sea turtles hatch and begin their journey to–well, to be eaten, frankly, although a few percent do make it to adulthood.
The first nest that I saw hatch emerged in the afternoon on a rainy day. Normally sea turtles come out of the nest and make their way to the water at night, and use cooling temperatures as a cue. Rain fools them into thinking it’s dark, and this hatch was making their break in broad daylight. We watched the baby turtles–each no bigger than a big kiwi fruit–flop awkwardly towards the water, alternating their flippers and dragging themselves forward. We shooed away the seagulls who watched us with petulant expressions, since the normal fate of a baby sea turtle hatching during the day is a short trip down a seagull’s throat.
But none of this is the behavior I was thinking of. Rather, the amazing thing is what happens when you pick up a baby sea turtle. Once the pressure of the sand beneath its belly is gone, the motion of its flippers magically switches from alternating to synchronized, both flippers flapping in unison like the oars of a sculler on Lake Union. Even more remarkable is what happens when you tilt the turtle from side to side, or front downward or upward. The rear fins, useless on land, become rudders, turning in just such a way as would correct the turtle’s posture in the sea so as to keep it level and moving straight ahead.
Tilt the turtle head down, both rear fins bend up. Tilt it to the left, the left rear fin bends down and the right fin bends up, while one front flipper stops moving and the other churns frantically. The newly hatched sea turtle needs to get out to sea fast, to avoid the predators in the reef along the way, and its coloring (dark on top, light on bottom) are optimized to make it difficult to see as long as it remains level.
This is what evolution does. It takes random variation and selects for those combinations that lead to reproductive success. If those variations have their root in genes, those genes get passed along. I’m curious to see if anyone tackles the question of how the turtle keeps steady, now that we have the tool of its genome to help. I’d love to learn what goes into hardwiring this kind of behavior and who knows? Maybe nature’s figured out some tricks that the cellphone makers don’t know.