Fastest Moving Islands, Part II: Evolution of a Species
Galapagos tortoise
By Rick Schleicher

Picking up from my last story. Why do the Galápagos giant tortoises live so long, up to two hundred years? I stated that the reason had to do with geology and plate tectonics. There are (or were) fourteen different species of Galápagos giant tortoises, each unique to their island or in the case of the island of Isabela, each volcano (there are four), except the scientists keep changing the number, some of the giant tortoise are extinct or were thought to be extinct. The Floreana giant tortoises were thought to be extinct, except they found one roaming around the highlands last year. The scientists found genetic differences in the giant tortoises on Santa Cruz, though they look the same, so now there are two on Santa Cruz. 

Scientists can drive you crazy. You might have heard of Lonesome George? This old guy was thought to be the last of his species from the island of La Pinta. The scientists were all concerned about preserving his gene pool and so set about attempting to mate him with a giant tortoise from a different island. This was not going very well so the National Park brought in a specialist, a buxom young doctor from, of all countries, Sweden. She did everything she could, apparently there was some massage therapy involved. I never was able to meet her, but there are/were plenty of stories. Better not to imagine.

Anyways, the giant tortoise species in the Galápagos, according to the scientists, is twenty-six million years old and yet the oldest island in the Galápagos is five million years old. This indicates that the tortoises have moved from island to island as the islands emerge and then sink. Now, obviously once or twice every million years a bunch of them did not get together, build a boat, name it the Mayflower and sail away in an effort to flee religious persecution. The closest thing to church I have ever seen any of them attend is feeding time at a breeding center. 

Photo by Barbara Anderson at Unsplash

What happens, near as the scientists can figure, is that, let’s say giant tortoise Fred, he’s minding his own business, but happens to be in a gully. It doesn’t “rain” very often in the Galápagos. What it does do is drizzle six months out of the year in the highlands and sometimes down near the coast, but when it does rain, usually February, it’s buckets and dogs and cats, two inches an hour. Every street in town becomes a river, the rivers become ragging and it’s hot so that you can be soaking wet, takes only a couple of seconds for that and you still want to get in front of an air conditioner. We’ve had a few tours when this happens, all fond memories, good things happen with the wild life. But there you have Fred and all he knows is he is heading for the highlands, crossing this gully. The next thing he knows is he is swept out to sea by a flash flood. Now tortoises float and can live for a year without food or water. So, Fred is floating out there in the ocean, hoping a killer whale doesn’t come by and eat him. He has another problem though, it’s the rainy season and so the prevailing winds that might have sent him towards a new island don’t exist. Even if they did exist or when they eventually return, that new island is fifty miles away. Pretty tough odds he is going to be blown that way. That island is a speck on the horizon. If by some odd chance the winds do blow him that fifty miles to landfall, he needs to land on one of the very few beaches in the Galápagos or else he will be dashed upon volcanic rocks by the waves.

Photo by Juan Zambonino at Come To Galápagos

But let’s say, by some miracle, he is blown to that island and he happens to land on a beach. Now Fred needs to eat and drink and in order to procreate he needs a girlfriend who also has to have survived the same very long shot circumstance as he did. He heads for the highlands, not waiting around on the beach for his girlfriend.

His cousin Johnny could not float that well, so he sank. His cousin Kevin could not last that long without food or water, so their gene pools don’t make the crossing. Fred makes it to the next island and he waits around for thirty years in the highlands for his girlfriend to arrive, but Fred dies two years before she gets there, his gene pool doesn’t survive. But, his cousin Bert, floats, can live without food or water and has a gene that allows him to live longer than Fred managed, as does Sally, Bert’s newly arrived wife who found Bert in the highlands, lonely, but well fed. 

And so there you have, plate tectonics affecting genetic evolution of a species.