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|Is Darwinian Evolution [Just] A Theory?|
Feb. 24th, 2009 at 8:25 pm
You’ll hear some opponents of Darwinian evolution say this sometimes, and it makes me laugh. If Darwinian evolution is merely a theory, that is small comfort. After all, gravity is “just” a theory, but for all that, gravity can mess with you pretty bad when you take a stroll off a third-floor balcony.
My beef with Darwinian evolution isn’t that it’s “just” a theory. It’s that it’s become more than a theory for some. A good theory, according to Karl Popper, should be falsifiable. Yet if we concede (unlike the Creationists) that the Earth is older than 6,000 years, that species can be created and go extinct at times other than the creation and the flood, and that species themselves can change over time and adapt to their environments, then can we still be absolutely sure that the only mechanism of species creation and change is Darwinian natural selection? How would we know if other mechanisms are operating sometimes?
All too often, Darwinian evolution functions as a heuristic, or a rule of thumb, rather than as a theory. A theory should help us make predictions, and certainly Darwinian evolution makes plenty of predictions. But most often, Darwinian evolution seems to preordain its own conclusion and then the “proof” is actually sought to show how natural selection produced the observed result.
As an example, let us consider how the leopard got its spots.I choose this story because it comes from a Rudyard Kipling series called “Just So” stories, written for children. Kipling tells us how the Leopard got its spots by taking fashion advice from an Ethiopian (who prefers the monochrome look for himself). These “Just So” stories are cute and pat and neat.
In practice, Darwinian evolution often functions in very same kind of “Just So” way as Kipling’s tales. How did the Leopard gets its spots? Because Leopards with spots make it easier to hide from their prey. How do we know that? We’d have to put Leopards out there in the same environment to test whether different kinds of spots, or no spots at all, cause them to kill less prey. But if we could show that spotless Leopards kill more prey than spotted ones, would anyone reject Darwinian evolution because of that? Maybe Leopards aren’t the best example, since they are actually going extinct and genetic studies show they’ve had quite a hard time of things for a long time, so spots or none, they aren’t too successful right now.
Darwinian theory says the best-adapted species tend to survive. How do we know they’re the best adapted? Because they survived. That tautology is awfully convenient for something that’s “just” a theory.
Now, a lot of work is actually being done on the evolution of ornamentation; it’s a problem that worried Darwin himself; he knew it presented a real threat to his theory. How do peacock feathers improve the species’ chances of survival? Sure, chicks dig it, but how does that advantage their offspring? And how can you prove it experimentally?
Most of this ornamentation work (at least that I am familiar with) has been done, not with peacocks or leopards, but with guppies. And what researchers find is that female guppies prefer to mate with brightly colored males, but that brightly colored males tend to get eaten. So in guppy ponds with lots of predators, the (surviving) males tend to look pretty drab, and so, therefore, do the male offspring. In the guppy ponds without predators, those drab males can’t get the females’ attention and so the brightly colored males tend to proliferate. Fine, but why the different breeding incentives for males versus females? What adaptive purpose does it serve the species to have brightly colored males? I don’t think there is one, though some have suggested that the metabolic skills required in synthesizing colors is expensive and difficult, so this shows the male has a lot of resources to spend on the female. That may be true for the peacock, but I do not think this is the case for guppies, where any differences would have to be minor.
For my part, I think female guppies prefer brightly colored males for the same reason we do: they’re more beautiful. We know something beautiful when we see it, and so does the female guppy. I don’t think it confers any selective evolutionary advantage; it’s simply that beauty is something to be universally desired. That answer, of course, is completely unacceptable to a pure Darwinian, who must keep seeking for evolutionary advantages bright colors confer.
Whatever your feelings about the evolution of ornamentation are, the key point here is that these answers have still not arrived. And yet, you don’t see anyone saying that we should suspend, or reject, Darwinian evolution because it cannot account for ornamentation. And there are similar difficulties with the mystery of altruism, where some valiant work has been done, but few would claim the problem has been solved.
Let us move to another example, which is Darwin’s claim that species adapt to best exploit the available resources, and how this relates to diversity. We are taught that rain forests have the most diversity of species. Why? Scientists theorize that it’s because they have the most resources: rich soils, abundant sunshine and water. Fair enough. But when biologists actually looked at it, they discovered that the number of species competing for sustenance in the available niches is much larger than elsewhere. Though the aggregate energy in the rain forest available is relatively large, the per species increment is smaller. And species compete much more within themselves than elsewhere in rain forests, so it’s pretty dog-eat-dog in there.
The upshot is, if you’re just starting out on the road of life, you’d rather be a bristlecone pine cone, nearly alone, on the top of a cold mountain peak, than the seed of a canopy tree, which has to survive all the predators, insects, and get a clear spot of ground to get sunshine. It appears that the rain forests are too diverse in proportion to the available energy, and other, more temperate climes, are not diverse enough, and so far, we don’t know why, and I think it’s fair to say Darwinian theory isn’t helping us figure out why. People are using Darwinian theory as a framework, or a heuristic, for how to consider the problem, but that’s it. They’re looking for the explanation within Darwinian theory, so there’s no way they’d discover something that falsifies Darwinian theory this way.
There are other puzzles that evolution and natural selection can’t seem to answer. Leaves are green because they need to reflect red, the most heat intensive wavelength of light. But this is only a problem in warm and hot climates. At higher latitudes, leaves and grass should be black, where overheating is no problem and adequate sunlight is. But that’s not what we see. Leaves are green everywhere. Why? If Darwinian evolution had really optimized every species’ niche, then there should be black leaves. I’m not saying this renders Darwinian evolution false, but I am asking, what would be proof that Darwinian evolution was false, or at least didn’t universally apply?
Could we agree on an observation, or an experiment, that, if a certain result was observed, would force us to restrict, or reject, Darwinian evolution in certain cases? I don’t think proponents of Darwinian evolution could even imagine such a test, nor would they agree to it. They are too used to looking at something already present in nature, and then using Darwinian principles to show how this is the preferred result. It’s a “Just So” story, where Darwinian evolution is the neat, pat, tidy answer already supplied.
But that’s cheating. It’s funny that so many proponents of Darwinian evolution love to trash religious faith, saying that the religious don’t accept evidence, but only accept evidence that fits their religious faith. I find Darwinian evolutionists do the same thing, all the time. They can try to pretend that their minds are open, but if you ask them to come up with an observation or experiment that would falsify the theory (and you don’t allow them to use their favorite Creationist straw men), they literally can’t imagine it. Far be it from me to criticize religious faith; I think such things are essential: no one can live his life only on the basis of what can be empirically proved beyond a shadow of a doubt.Â I just think we should recognize Darwinian theory for what it has become: more than a theory, a dogma.
That doesn’t mean it isn’t useful, but I don’t think it makes it a theory. To go back to the gravity example, we have Newton’s thoughts about gravity, but then Einstein revised it with his theory of space-time. And now others are talking about quantum gravity. There are in fact several theories of gravity. Just as there could be several theories, perhaps all of them true in certain cases, of how species are created and change over time. Yet biologists don’t seem open to this, despite some evidence of non-Darwinian evolutionary mechanisms operating in species change.
Can we find cases where things exist that don’t seem to be accounted for by natural adaptation or improved survivability? I have offered up a few examples earlier in my post, but I’ve saved the best example, in my opinion, for last: How can Darwinian evolution account for the human brain?
The human brain only comprises 2.5% of the body’s weight, but consumes fully 20% of its energy. It’s a greedy consumer of glucose and oxygen. In newborns it’s even worse: fully 60% of the newborn’s energy is going into its brain, and it doubles in size in the first year after birth. And it takes an incredible amount of time before a human is able to survive on its own. All this energy is going for what? Is all that intelligence really improving survival? No other animal on earth comes close to spending, metabolically, what we do on running our brains. It is a huge risk to take, and it causes a huge hit in survivability, especially in children (which is what would affect species’ success the most, because children have not reached breeding age yet).
The human brain is an amazing thing, but it is far in excess of what we would need just to hunt lions on the veldt, fish in the ocean, or pick fruit from trees. I’m not saying that the human brain didn’t evolve; the fact that we find genes in our brains that are very similar to mice and even fruit flies testify to our common genetic heritage. And I am very aware of the great number of theories that have been advanced to explain, from a Darwinian standpoint, how a human brain could be produced. But the work on the evolution of intelligence is so preliminary, no one can pretend that any of these theories has a great deal of support at this point. And until we know more, anything anyone says about the evolution of intelligence is conjecture or dogma. It is very far from proven that the adaptations and changes we see in the human brain came solely due to pressures of natural selection.
Stephen Jay Gould poo-poos the uniqueness of the human brain, saying it is only because we are humans we find it unique. He says, if elephants could talk, they could rhapsodize about their incredible trunks. And an elephant trunk is an amazing thing. But elephants can’t talk, and they can’t rhapsodize about anything. If the human brain could only rhapsodize about itself, then it wouldn’t be a very interesting organ. And much more often than being amazed at itself, it is amazed at elephants’ trunks, leopards’ spots, green leaves, and a whole host of other things. It can ask questions and digest patterns and communicate subtleties that birds, whales, and chimps cannot. The human brain is not just unique, it is uniquely unique.
John Gardner in his book Grendel calls humans “pattern eaters,” which is a very good name for what our brains do. Some times we make fun of this, as in when people find Elvis’ profile in burnt toast or the Virgin Mary in the stump of wood. But this same pattern-eating is what led us to discover the electromagnetic spectrum of light and energy, which enables me to post these thoughts.