If you teach evolution, or like to read about it, there’s a new paper you should read by Kevin Padian in the journal Evolution: Education and Outreach (free download; reference below). It’s a discussion of misrepresentations about evolution that occur not only in popular science writing, but also in textbooks. As president of the National Center for Science Education (NCSE), and a respected paleontologist at Berkeley who works on the evolution of birds and flight, Padian carries considerable authority in this area. And indeed, his points are generally good. In fact, I was embarrassed to see that I’ve been guilty of some of these misrepresentations, for which I’m sometimes called to account by readers here.
I do have a couple of disagreements with Padian’s points (more below), but on the whole they’re solid and worth absorbing. Here are some that I agree with, or at least don’t strongly disagree with:
- Define evolution properly. My own definition is “change in allele frequency over time,” but Padian doesn’t like that: he prefers Darwin’s definition of “descent with modification”. I’m neutral about this. Padian doesn’t like the gene-frequency change definition because such changes could reverse themselves, nullifying evolution. But so can “descent with modification”. Further, it’s not clear what, exactly, gets modified? Nevertheless, I’m happy to adopt Padian’s change as a supplementary definition to my own.
- Avoid the term “modern” when referring to traits or species. To Padian, this implies progressivism, and we know evolution isn’t really on a one-way march to ever-better organisms. I’m neutral about this change: I don’t see the harm of referring to “modern reptiles” as opposed to “Jurassic reptiles.”
- Don’t use the term “many scientists believe.” This is because “many” implies that science is decided by vote; “scientists” could refer to those outside the field of expertise (for example, it’s fair to say “many scientists doubt evolution”, though most of those misguided doubters are chemists, engineers, and the like); and “belief” is not something scientists have. “Confidence based on evidence” is better, and avoids the religious implications of the word “believe.”
- Avoid the words “primitive” and “advanced.” Padian sees these as carrying value judgments similar to that of the word “modern.” He prefers the term “basal” and “derived,” which come from cladistic systematics. I’m perfectly happy to adopt those terms, though they may be confusing in popular-evolution texts.
- Don’t personalize scientific debates. As Padian notes, “this example [the argument about the closest living relatives of whales] was not about individual scientists arguing with each other, but about the kinds of evidence that scientists in certain fields are trained to understand and preferentially accept.” I mildly disagree with this, for it gives the impression that science is not a human enterprise, and that personalities play no role in the progress of science. Ultimately, of course, truth wins out, but the force of certain personalities, or the unwillingness of scientists to admit they’re wrong, does affect progress in some fields. Think about how long the influential Steve Gould, for instance, delayed progress in paleobiology by insisting that punctuated equilibrium was not just a description of a jerky pattern in the fossil record, but was caused by a process that was essentially non-Darwinian (founder-effect speciation combined with species selection, processes that have not won over many evolutionists).
- “Use care in characterizing the religious beliefs of historical figures.” Yes, people often get this wrong, as when implying that Darwin was religious or Cuvier a biblical literalist. But I’m not sure what real harm is done by this, except by creationists who insist that Darwin was either conventionally religious or recanted his agnosticism on his deathbed.
- “Avoid giving the impression that evolution is atheistic, or that evolutionists must be atheists.” Well, yes, one should not give this impression when teaching, for it’s an intrusion of religion into the classroom. But evolution is atheistic in the sense that all science is atheistic: we don’t assume that divine powers are working through the process. That’s what we mean when we say “evolution is materialistic and unguided.” Now people like Genie Scott at the NCSE don’t like that language, either, but it’s no more wrong than saying that chemistry is materialistic and unguided. The objection to the “unguided” part (an objection Scott made when the evolution statement was adopted by the National Association of Biology Teachers) is a purely political ploy, meant to avoid alienating religious allies. But, as I’ve said repeatedly, theistic evolutionists are not the allies of scientists. As for the impression that “evolutionists must be atheists,” I don’t really say that, but I think that consistent evolutionists, as with all consistent scientists, should be atheists. Otherwise they are simultaneously adopting two disparate methodologies for finding “truth.”
- Do not personify natural selection. A good point, and one I’ve been guilty of violating. Natural selection is not some force imposed on organisms by the outside, nor does it “want” anything. It is simply a process of gene sorting—a description of what happens when some forms of genes leave more copies than others.
Likewise, Padian says that we shouldn’t claim that natural selection is “creative,” for that also personifies a process that is impersonal. I’m not so sure about this one: is substantial harm done by desribing the “creativity” of selection if one is clear what one means—selection has produced organisms that are well-adapted to their environments, and appear designed by a creator? Still, Padian is correct to say we should avoid describing natural selection as anything other than differential reproduction of genes, or saying that is has foresight. Another of Padian’s beefs is the term that a feature evolved “for” something, as “the flippers of dolphins evolved to help them swim.” That, too, mischaracterizes what really happens during natural selection.
But I disagree strongly with three of Padian’s prescriptions. Two are scientific, and one philosophical.
- “‘Fitness’ is not about how many offspring you leave.” Padian doesn’t like this characterization of a fundamental concept in evolutionary genetics, noting that “It is not about the number of offspring you produce; it’s about their survivability.” But few evolutionists, whether in technical or popular books, think that pure number of offspring is the whole criterion for fitness, and few characterize natural selection as “survival of the fittest.” Rather, most of us think of fitness as the relative success of an allele or a genotype in reproducing itself—in leaving copies for the next generation. n that sense it is about the number of offspring (or gene copies) that you have, if by that you mean “number of surviving offspring”. For the offspring that constitute the next generation are the offspring produced, weighted by their probability of surviving to reproduce.
- “Sexual selection is not a kind of natural selection.” To me, this is the biggest problem with Padian’s list of scientific misconceptions, for virtually every biologist recognizes sexual selection as a subset of natural selection—the subset that involves mate choice. And the boundaries between natural and sexual selection are very fuzzy. For example, male sage grouse who dance the most vigorously on a lek (a mating arena) are chosen more often by females. That’s sexual selection. But males who are able to displace the sperm of previously-mating males (dameselflies, for instance, have “penis scoops” that remove the sperm from previously males when they inseminate a female) are often regarded as experiencing natural selection. What about males who produce sperm that swim faster than those of other males, or more sperm? Is that natural or sexual selection? The distinction is not clear cut.
Padian sees sexual selection as different from natural selection because sexual selection produces differences between males and females: sexual dimorphisms like male ornaments, the bowers of bowerbirds, and male calling behavior, as in frogs. Padian notes correctly that it was Darwin who came up with the idea of sexual selection—and gave it its name—because he observed male traits that were deleterious for survival (e.g., the long tails of male widowbirds). His explanation was that the survival disadvantage was more than compensated for by the mating advantage (females like long tails).
Padian’s basis for saying that sexual selection isn’t natural selection rests on this statement: “Because Darwin invented sexual selection, and because he based it on observations that have never been falsified, his definition cannot be wrong.” I find that very strange. The inventor of a term doesn’t enjoy lifelong propriety over its correctness. Besides, sexual selection operates in precisely the same way as natural selection: the differential reproduction of genes for behavior and morphology. To say that they are different processes is to perpetuate a misunderstanding.
Finally, natural selection can also lead to sexual dimorphism, as with raptors of different sizes that are ecologically specialized: males and females are different because they catch different-sized prey. Female Drosophila may be larger than males because large body size enables you to lay more eggs. Dimorphisms can result from natural and sexual selection. Too, there are forms of sexual selection that don’t lead to dimorphisms. There is mutual sexual selection, for example. If both males and females have evolved to find the color red attractive—perhaps because they need to find nutritious red berries—it’s possible that both sexes would prefer, as a sensory byproduct, red plumage in the other sex. That would be sexual selection, but would lead to identical coloration of males and females, not dimorphism. This may, for example, explain bright colors in male and female parrots or reef fish.
- “Avoid pitting science against religion, even though sometimes there are real conflicts.” As president of the NCSE, which is explicitly an accommodationist organization, I see this advice as not only self-contradictory (“don’t say there are conflicts even though there are”), but a purely tactical ploy to win friends for evolution among the faithful. True, I don’t talk about religion in my undergraduate science classes, but I surely mention the conflict in my popular writing, as in my Evolution paper about American rejection of evolution. It’s impossible, in fact, to understand the rejection of evolution in any nation without mentioning religion. Creationism is explictly the pitting of science against religion.
In trying to keep religion and science in separate magisteria, Padian is forced to make dubious or insupportable statements, including the deeply misguided notion that science can’t deal with the supernatural. How many times do I have to correct this elementary mistake? Science can test claims about rain dances, intercessory prayer, spiritual healing, ESP, astrology, and all kinds of supernatural claims. Padian also claims that science cannot disprove supernatural beings. Well, yes, but we don’t “prove” or “disprove” anything in science. But we surely can render suppositions about the supernatural unlikely. Here’s a bit of Padian’s discussion:
“Oddly, perhaps, the very openness of science is what attracts scorn from religious fundamentalists, who build their lives on what they accept as immutable truths of
faith. The principal act of faith of a scientist is accepting that the natural world is knowable, and that we can use our (however imperfect) faculties and judgment to learn about natural phenomena and trust our results, wherever our investigations lead. After that, the rules of scientific inquiry are not about faith, but about posing and testing hypotheses. But science has its limits, and the supernatural is one of them. In short, science does not deal with the supernatural. Religion has its limits too, and one of them is in making statements about the natural world. There is only conflict between science and religion if people want it; or rather, there is conflict when people want it.
. . . All science is non-theistic, by which is meant that it does not entail or require any concept of a god or other supernatural being or force. In fact, science is completely independent of any ideas about gods or other supernatural beliefs. But science is not anti-theistic: it does not deny such beings or forces, any more than it accepts them (or leprechauns or unicorns), because these things are not within the purview of science.”
Let me first dispel the notion that we scientists have “principal acts of faith” that the world is knowable. We don’t begin with that a priori presumption. Rather, the comprehensibility of the natural world is the result of experience, first tentative and now entrenched. Science now proceeds as if the world is knowable because all our experience confirms it. That isn’t faith, but confidence born of time and tribulation.
Further, Padian surely doesn’t think that science is independent of any ideas about unicorns, leprechauns, fairies, ESP, and astrology because “these things are not within the purview of science.” Of course they are! Theistic gods, like fairies and astrology, predict certain phenomena about the world that aren’t observed, thereby diminishing the likelihood that such things exist. The only kind of God immune to empirical study is a deistic God who doesn’t interact with the world—the kind of god that most believers don’t accept. So again Padian, like all of those who claim a disjunction of science and the supernatural, is making a theological rather than a scientific statement. If God is powerful, good and interactive, there should not be natural evils in the world, and we should have evidence for God’s existence. We don’t. Therefore God is unlikely—at least a theistic God who is omnipotent and omnibenevolent. If you are a Native American and perform rain dances during droughts, that notion can be tested, too. Just use a control group that doesn’t dance. Likewise for Christian Science and its idea of spiritual healing.
I’ve dwelt on my differences with Padian’s piece not because the piece is bad, for it isn’t; in fact, it’s quite good. But it takes longer to correct errors than to praise good stuff. I recommend Padian’s article to everyone who teaches or discusses evolution, but do be aware of the three potential problems I’ve just discussed.