The Human Condition:

Evolution as Adaptation – September 1, 2013

Turtle’s Spine

A recent issue of Science1 has a fascinating article about the development of turtle shells. Since the turtle’s shell is anchored to its ribcage and not an independent piece of external hardware like a crocodile’s hardened scales or armadillo’s bony plates, the question arises whether the turtle’s shell is an outgrowth of its skin, which then attached to the bones, or an outgrowth of the rib bones, which then replaced the skin. Scientists have studied the genetic development of turtle embryos and the development of soft-shell turtles, but they still can’t agree. Some even think different turtle species developed their shells along one or the other pathway.

This argument reminds me of a central fact of evolution. Nothing new arises on its own. The body parts we see all around us each had to be adapted from something else. Forelimbs with fingers evolved into single hooves by simultaneously shrinking the parallel bony structures of the digits into shin splints along the middle finger and pushing the nail out into a semicircular block of keratin for the hoof. Forelimbs with fingers evolved into wings by simultaneously shrinking the humerus and elongating the radius and ulna, stretching the forefinger into an even longer strut while shrinking the others into nubs, and pulling the skin of the arm skin further down the torso to make a pliable membrane. And the latter happened at least three times in evolution: once when certain reptiles evolved into pterodactyls, again when a different class of dinosaurs evolved into birds, and still once more when certain mammals turned into bats.2

None of this is design by what we would think of as intelligence. That is, someone sits down and asks, “How would I achieve this?” And then this mythical someone forms an image in the mind’s eye of the sorts of parts required to fit the purpose: a hard block with suspending struts and elastic bands to take shocks on stony ground, or a framework of struts and tissues to bend the wind. And finally the creator pulls out a sketchpad and creates the imagined structure in bone and muscle and skin, then translates those parts into the appropriate proteins. That’s design by intent, and it’s not what happens.

Instead, certain changes in the environment require the entire organism to change its life patterns or else decline and eventually disappear. Some members in each generation experience a small random change that either pushes them toward a new pattern, or pushes them away from it, or does nothing at all, or kills them outright. Most members of the species continue to struggle and fail. But those who get a little closer to being able to cope with the change succeed in proportion to the rest of their generation. If their offspring fail to inherit the change, they die and take the genetic change with them. If they inherit the change, they may succeed and breed again. And if they inherit, along with the original change, another tiny change that pushes them even further toward the successful pattern, their chance of success is even greater. And so it goes.3

The environmental background changes slowly or fast. The players in niches within that background either move toward a successful new life pattern or die out. The nature of the inherited change is random, for good or ill. What is not random is the effect of that change: it is tested in the environment and has either no effect or it succeeds or fails. Success—in whatever shape and on whatever terms the environment demands—is the only criterion.

Three things are certain. First, no species gets to a completely new and successful form all at once in the first generation. However, some species or individuals who may have been struggling in the old environment may find new opportunities as the environment changes around them. These species get a free head start on change. But it’s only a small advantage.

Second, these small random changes are happening all the time and in all directions of a better or worse fit to the environment, or to no apparent effect at all. Most of the changes are unimportant, or only slightly debilitating, or slightly helpful, or—occasionally—immediately lethal. Only when the change happens to fall in line with the direction in which the environment is already pushing the species does this small random change create the conditions for marginal success.4

Third, even when a favored individual inherits a change, and perhaps improves on it through mutation at the point of inheritance, and passes it along to the next generation, that individual will still die and disappear. Every individual dies, having made the best use he can of the equipment he inherited. Evolution relies on death, generation after generation going down to nothingness, just as the butcher, the baker, and the candle maker rely on their customers consuming their products, making them disappear, and coming back for more.

Evolution is not cruel. No more than a flash flood, a forest fire, or a tornado is cruel. These things exist, and they may be good for some organisms and bad for others. Sometimes you need to clear the ground unexpectedly so that other species get their chance to try their adaptations.

Evolution has only one rule: what works survives. Even if it’s ugly, like the nasal apparatus of a star-nosed mole. Even if it crosses previously established boundaries, like the duck-billed platypus. Even if it’s ungainly and improbable like the giraffe or the kangaroo. If it works, it survives.

If you require the universe to yield only perfectly logical and beautiful results, you won’t like evolution. If you require the universe to be motivated by thought, generosity, caring, and pity, you won’t like evolution. If death distresses you, you won’t like evolution. If the universe worked exactly the way you wanted it to, it would be a smaller place filled with more sameness.

But the universe is vast and complicated, where anything is possible. And that is a beautiful thought in itself.

1. Naomi Lubick, “Biologists Tell Dueling Stories of How Turtles Get Their Shells,” Science, Vol 341, 26 July 2013, p 329.

2. This haphazard tendency to use existing parts is one of the reasons why, after 120 million years of evolution, the top speed of a bird in level flight is still only about 50 miles an hour and, in diving flight, just over 100 mph. Consider that less than a century after the Wright brothers flew in North Carolina, the top speed of an airplane was Mach 3, humans had achieved orbit at about 17,000 mph, and landed on the Moon. And that’s my best argument against evolution by intelligent design.

3. See also Evolution and Intelligent Design from February 24, 2013.

4. “Marginal” in this instance refers to its original meaning: being at the outside edge, the far end of the curve, the next to last thing we try.