Sunday, July 18, 2010

Getting Darwin wrong

kw: book reviews, nonfiction, evolutionary theory, polemics

I can just hear all the biologists and paleontologists saying, "For pity's sake, don't publish that! We've got trouble enough in the trenches against the Creationists!!" But no, they just had to do it: Enter What Darwin Got Wrong by Jerry Fodor and Massimo Piattelli-Palmarini. To jump to the chase, the statement that is sure to get everyone's attention is their conclusion, that "there isn't any theory of evolution."

So what did Darwin get so wrong? It wasn't proposing that evolution is happening and that new species are produced from existing ones. It wasn't even his lyrical descriptions of the spreading diversity of living things, as exemplified, for example, by the finches that had "obviously" radiated from a founder population that came to the Galapagos Islands not too many thousands of years ago. Rather, it was his proposal of a mechanism for evolutionary change and innovation, for which he proposed the name natural selection, as somehow analogous to the artificial, human-directed selection that has produced many dog breeds from the primordial wolf, many pigeon breeds from the rock dove, and many breeds of cattle from the aurochs.

There genuinely is a serious problem with this analogy: artificial selection is mindful, but natural selection is mindless. In fact, to be a viable theory of evolutionary change, it is required to be so mindless that it is very, very hard for us mindful creatures to imagine it. We mostly don't. Instead of doing the hard cognitive work to discern the natural history sequence that may have led to a particular hummingbird species, for example, most writers produce "just-so stories" filled with intentional language. The hummingbird's ability to nearly stop its heart overnight when it can't feed is typically described as a reaction to the bird's "need" to conserve energy. I have yet to see a depiction that begins with a pre-hummingbird, which was probably larger and had plenty of energy to survive the night, a description that shows how, by various stages, as a population of nectar-feeding opportunists became one of nectar specialists, the entire physiology of the birds changed, one part of which being the development of a more variable metabolism.

Generalists becoming specialists. Is such specialization some kind of natural law? It is sometimes stated as such, as though it were as infallible as the law of gravity. But this kind of language sounds like there is some mind directing things behind the scenes. Perhaps Darwin did not make his argument sufficiently clear. He proposed an entirely mindless process, which nevertheless produced a result (many, many results) that we, with our pattern-detecting and -generating minds, think of as "progress".

I could go very long here, and I gathered a lot of quotes from the book, with some intention to take up the cudgels on behalf of natural selection. I think the theory of natural selection is quite valid, but I have to agree with this book's authors that Darwinists and Neo-Darwinists are guilty of a great deal of sloppy thinking. So I will do my best to keep this short, and merely present a few points worth considering. For a longer discussion of related points, see my posts of July 13, July 15, and July 17.

First and foremost, if a creature is alive, it is taking advantage of a flow of energy from some source to some sink. Most life on earth lives courtesy of Solar energy, but some lives instead on energy released from Earth processes, or stored chemical energy left over from the formation of Earth. For simplicity, I'll consider some animal in the food chain that begins with plants that photosynthesize Solar energy and ends with the decomposition of the animal, or its predator, by fungi and bacteria. The requirements for this animal's sustenance are: something to eat; sufficient water, either for it to drink or such that it won't desiccate (maybe it lives in water); a range of temperature in which its proteins work right; a low enough population of predators that it can live a while; and safe places to hide when predators are around. But this animal was born, and if its species is to continue to exist, there are a few more requirements: other members of the species (or the population) sufficiently close by that it can find a mate (we're assuming a sexual species here) and a level of stability in its environment that is tolerable, during this animal's productive and reproductive life span. There may be requirements I haven't thought of, but this is a sufficient set to make the point.

That collection of requirements describes what is often called the "niche" for a species. This is useful shorthand, but we must use care to avoid circular language. Creatures tend to create the niches in which we find them. There is no pre-existing niche that yawns expectantly until just the right critter comes along. Consider rabbits and Australia.

There were no rabbits in Australia until some well-meaning humans brought a number of breeding pairs there in 1859. The conditions over a large part of the continent are ideal for rabbits. Accounts abound of the awful consequences of their spread there, to the point that two million could be killed yearly and have no noticeable effect on the population. Was there a niche for rabbits, awaiting their arrival? No, there were other grazing animals that had been making full use of the native plants. Their populations waned as rabbits spread. Though this is natural selection in action, no new species have so far been produced, though a few may have gone extinct. In time, perhaps the local predators will get better at hunting rabbits, and a new species of marsupial rabbit hound may arise. Unless, of course, humans find an appropriate rabbit disease with which to eliminate them.

Let us consider a longer span of time into the future, say 100,000 years. That is a lot of rabbit generations. If Australia still has rabbits, it is likely that a few species of more specialist rabbits will have evolved. Some might eat mostly grassy plants and their seeds (as the rabbit in my yard does); some may eat more woody fare; some may get better at swimming and eat marsh plants, though they'll have to watch out for crocs. Why is this? When an environment is "too rich", as Australia is, in rabbit terms, the development of specialist species is favored because the total of their populations exceeds the population of a more generalist species that is less efficient at metabolizing a wider range of foods.

This, by the way, is the kind of prediction that natural selection allows us to make. It is no empty theory, as our two philosophers would have us believe. Theories have two principal uses: to explain what we see, and to predict what might happen as a consequence. Some theories, such as Newton's theory of gravity, or Einstein's general theory of relativity, are sufficiently exact that they can be used to make very exacting predictions of such things as the dissipation rates of globular clusters of stars, or of the position of the planets and their moons for many centuries into the future.

The theories of natural history, and most particularly evolution's theory, natural selection, deal with much more complex systems, and their predictions are correspondingly less precise. Natural history and paleontology show us that mammal species tend to survive for between one and four million years, before either evolving into new species or going extinct. However, we know of mammal species that are quite a bit older than four million years, and we are finding out how easy it is to drive even young, thriving species to extinction by hunting or habitat destruction. So the "one to four million years" species lifetime is no more than a historical range, and cannot be taken as a natural law. But it allows us to say that, were we to invent a time machine and jump twenty million years into the future, very few of today's species of mammals would still be in existence, and while a similar total number of mammal species would likely be found (unless humans are still around and have really messed things up), most of them would be just one or two million years old.

Finally, I must agree with the authors in decrying the tendency of many to say that natural history can produce anything. They ask, "Will pigs fly?" and they answer, only if their weight, musculature, and number of limbs change (they also posit feathers, but bats fly without feathers). Let's see, reduce the weight so wings don't have to be 747-sized; instead of adding limbs, reconfigure the front limbs; change the forelimb and forehoof into some kind of flying surface...well, I can see the direction this is going, and that "niche" is already filled, with the flying foxes, the large tropical fruit bats.

But the point I'll make, enlarging one the authors make, is that natural selection has to work with the changes that mutations can produce from already-living creatures. You can't have a hand without an arm (well, you can, if your mother took Thalidomide during pregnancy, but it isn't a very useful hand). It seems that natural selection hasn't deviated from the humerus-ulna-radius scheme for arm bones of mammals and birds, but the number of "finger" bones has varied. Some humans have six fingers, and I know one man with no thumbs, just five fingers on each hand. Equids have one "finger" in each foot. While it can be thought of, to have an extra bone accompany the humerus in the upper arm, the present arrangement is "good enough" and has never been improved upon.

The authors do not propose a new theory of evolutionary mechanisms. They say there isn't one, and simply propose that we stick to descriptive natural history. I think a point or two that I have made, in an elementary way perhaps, show that natural selection is a useful theory. It gives us language with which to describe how populations change through time. It accompanies the fact of evolution and provides explanatory power. It is easy to misuse, and Drs. Fodor and Piattelli-Palmarini have done us good service to point out the many ways it has been misused. But let us not discard the theory just because it has been misused. We don't discard our hammers, just because a hammer is occasionally used as a murder weapon.

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