Darwin As Prognosticator
How good was Darwin at making predictions? A good scientific theory should make predictions, at least according to a common assumption about science. PBS thinks Darwin hit a home run, according to an interactive feature on the website for Judgment Day, the documentary about evolution vs intelligent design shown on Nova this week (11/14/2007). The commentary below will analyze these 13 predictions, but some other recent stories from science journals show Darwin scoring a much lower batting average:
- Island dwarfism: Evolutionary biologists have long believed that animals trapped on islands would evolve into smaller versions of their mainland counterparts. Not true, say researchers from Imperial College, London. A catalog of island species shows no such trend; many factors are involved in the size distribution of island species. The details can be found at PhysOrg and Science Daily. (Note: the articles do not attribute the prediction to Darwin himself.)
- Arms race: If Darwin intended his theory of natural selection to express a law of nature that applies everywhere, it might be difficult to correlate opposite results. Many evolutionary biologists speak of predators, prey and parasites leading to an “evolutionary arms race” that drives speciation and adaptive radiation, leading to Darwin’s branching tree of life. An article in Science Daily, however, says that predators and parasites can drive “evolutionary stability.”
- Parental guidance suggested: The environment is supposed to drive evolutionary adaptation. Offspring, facing the mean old world, should get by with the random genetic mutations that improve their survival – not a parental handout. Taking loans from mom or dad’s genes would indicate a dependency on pre-adaptive resources, innate in the genetic information of the species. A study at University of Virginia suggests, however, that maternal influences do help offspring adapt to their environment.
- Birds don’t talk: What drives speciation in birds? It should be Darwin’s mechanism of natural selection – of which the Galapagos finches are the textbook example. In Science last month,1 however, Loren Rieseberg reviewed a new book by Trevor Price, Speciation in Birds, and found that even the textbook case is not open and shut:
Of perhaps greater interest are Price’s conclusions about the roles of ecology and social selection in speciation; these remain relatively unexplored subjects about which birds have much to offer. Closely related species of birds often differ in ecologically important traits–such as body size, habitat preferences, and feeding and migratory behaviors–that are also likely to contribute to both premating and postmating reproductive isolation. These observations, combined with classic studies of ecologically driven speciation in Darwin’s finches and crossbills, imply that ecological selection likely contributes to most speciation events in birds. However, Price cautions that divergence of most co-occurring bird species is too ancient to make inferences about the causes of speciation and that studies of recently diverged species, such as Darwin’s finches, highlight the fragility of ecological reproductive barriers. He concludes that “it is unclear if ecological causes are sufficient or even important in many speciation events.” This somewhat negative assessment of the role of ecology in speciation is tempered by speculation in later chapters that rapid ecological speciation may account for short branch lengths detected early in the evolution of many bird genera.
That sounds like Price debunked Darwin’s speculation, only to replace it with one of his own. “Interestingly, social selection appears to be more generally important in speciation in birds than sexual selection, despite the emphasis in the literature on the latter,” Rieseberg continued, only to accuse Price of doublethink: “Price also argues that ecological factors are a major cause of divergence in socially selected traits, an assertion that, while strongly supported, seemingly is at odds with his earlier pessimistic assessment of the importance of ecology in speciation.”
Earlier in the review, Rieseberg also noted that Price did not put much credibility in another evolutionary hypothesis, the so-called “founder effect” (i.e., that new colonizers drift genetically into new species). Whatever the causes of the origin of species, they appear more complex and inscrutable than Darwin had imagined.
- Opportunity lost: The genes of 12 species of Drosophila were compared in a massive test of evolution, published in Nature.2 How much opportunity was there for evolution since the species diverged? The team wrote, “the evolutionary divergence spanned by the genus Drosophila exceeds that of the entire mammalian radiation when generation time is taken into account,” so for the number of generations during which mammals went from mice to giraffes and whales, these little flies should have had ample opportunity to evolve by Darwin’s theory of natural selection. (Note: the only kind of natural selection of interest here is positive selection for functional advantage; purifying selection gets rid of harmful mutations, and balancing selection tries to offset them.)
The paper mentions evolution and selection numerous times. A search for innovation turns up empty, though, and examination of instances of positive selection shows no clear cut example of something new and improved arising. The geneticists looked for markers of positive selection indirectly – fast-changing base pairs in otherwise unchanging sequences. It is not as straightforward, however, to correlate these changes with new genetic information that provides a functional advantage for the fly. The clearest example of positive selection they could find was for “helicase activity,” which seems like merely an adjustment in the rate of operation of existing hardware. They said, “Despite a number of functional categories with evidence for elevated omega [i.e., an indicator of positive natural selection], ‘helicase activity’ is the only functional category significantly more likely to be positively selected.” In other words, not only are all the 12 species of Drosophila still fruit flies, none of them seemed to exhibit a single clear-cut example of a new functional innovation – despite as many generations as the mammals had for their assumed evolutionary radiation, with all the new capabilities possessed by bats, skunks, hippos and aardvarks. What was Darwin doing all that time? It would seem if clear indications of innovation that would vindicate Darwin had been found, it would be the news of the decade.
In the same issue of Nature,3 Ewan Birney commented on the Clark et al study. “The analysis of positive selection by Clark and colleagues is undoubtedly the broadest and most detailed investigation performed in any clade of multicellular organisms.” Two species of Drosophila in the study are as different genetically as humans are from other primates, he said. Though he claimed that the team identified a third of fruit fly genes apparently undergoing positive selection (mostly for the existing immune system and olfactory functions), he did not identify any example of an “upward” change that gave any species a new organ, system, or innovation that would indicate Drosophila was evolving into something better than a plain old fruit fly. Instead, he indicated that future studies on primates would be required to understand positive evolution: “Clark and colleagues’ findings suggest that, to understand the fascinating adaptive changes among primates, including those unique to humans, we probably need to sequence the genome of every extant primate (and, where possible, any extinct primates with recoverable DNA), using optimal sequencing strategies to obtain both population-level data and accurate genome sequences.”
- Fossils to the rescue? Is Darwin’s tree rooted in the rocks? Gene Hunt undertook a study of “The relative importance of directional change, random walks, and stasis in the evolution of fossil lineages,” and found a lot of stasis. After his “large-scale, statistical survey of evolutionary mode in fossil lineages,” involving some 250 sequences of evolving traits, he wrote in PNAS,4 “The rarity with which directional evolution was observed in this study corroborates a key claim of punctuated equilibria and suggests that truly directional evolution is infrequent or, perhaps more importantly, of short enough duration so as to rarely register in paleontological sampling.” Darwin did not predict punctuated equilibria. The core of his theory was that changes occurred imperceptibly, gradually and cumulatively. In addition, he knew that the fossil record was characterized by large gaps, but predicted that the new fossil discoveries would fill in those gaps, revealing his hoped-for branching evolutionary tree. Hunt found only 5% of fossil lineages could be attributed to directional evolution. Of the rest that showed change over time, it was mostly for body size, not body shape. This does not seem to be a vindication for Darwin’s prognosticative powers. In the evolutionary rat race, if a bigger or smaller rat wins, it is still just a rat.
Scientific literature does present occasional successes for Darwin, such as this claimed vindication at Queens University for Darwin’s controversial hypothesis of sympatric speciation. But the score is mixed. One study never undertaken is how Darwin’s predictions would rank against those of astrology.
1. Loren H. Rieseberg, “…And a Partridge in Allopatry,” Science, 12 October 2007: Vol. 318. no. 5848, p. 198, DOI: 10.1126/science.1147892.
2. Clark et al, “Evolution of genes and genomes in the Drosophila phylogeny,” Nature 450, 203-218 (8 November 2007) | doi:10.1038/nature06341.
See also an article in Science Daily that lamented the difficulty this study uncovered about identifying what is a gene.
3. Ewan Birney, “Evolutionary genomics: Come fly with us,” Nature 450, 184-185 (8 November 2007) | doi:10.1038/450184a.
4. Gene Hunt, “The relative importance of directional change, random walks, and stasis in the evolution of fossil lineages,” Proceedings of the National Academy of Sciences USA, published online before print November 14, 2007, 10.1073/pnas.0704088104.
We have reported numerous times when Darwin predicted something and the opposite was found (e.g., 11/13/2007, 11/09/2007, 10/17/2007). Charlie has struck out again and again, yet his fans never give up.
The PBS Judgment Day program (11/14/2007) made a big deal about how “scientific” Darwin’s theory was. For support, the PBS website offered an interactive feature listing 13 of “Darwin’s Predictions” that supposedly came true. This was presented to trick students and visitors into thinking Darwin has an impressive batting average. Let’s look at them and see if Charlie can make it to first base at least. The PBS feature begins with a dramatic star spangled banner, asking Jose if he can see the Darwin’s early light:
Ahead of his time is putting it moderately for Charles Darwin. The father of evolution had conjectures that were only proved, or greatly substantiated, decades after his death in 1882, in some cases not until recently. Today, evidence that unequivocally supports his theory of evolution by natural selection, as well as other surmises he had, comes from an array of scientific disciplines, including paleontology, geology, biochemistry, genetics, molecular biology, and, most recently, evolutionary developmental biology, or “evo devo.” “The notion that all these lines of evidence could converge and give a common answer to the question of where we came from is truly powerful,” says Brown University biologist Kenneth Miller. “This is the reason why scientific support for the theory of evolution is so overwhelming.”
A pretty dramatic overture indeed, provided there is power behind the sound system. Here are the 13 pitches for Darwin to swing at. Keep in mind these are all supposed to be predictions by Darwin that were confirmed by science. Unfortunately, since the Darwin Party owns the stadium and both teams, which are sworn to make Charlie look good, all we can do is umpire from the sidelines when they break the rules.
- Evo-devo: “Evolution happens,” the first entry announces triumphantly. Something else on bumper stickers also happens, but we won’t press the point.
Right off the bat, we notice them including evo-devo in the victory circle with little more than an unsupported assertion followed by the favorite Darwin Party quote that nothing in biology makes sense except in the darkness of evolution. Last month, however, Ron Amundson, in a Science Magazine book review (318:5850, pp. 571-572, 10/26/2007) portrayed evolutionary genetics and evolutionary embryology (of which evo-devo is the latest incarnation) as antagonists in a long tug-of-war between biologists about where the seat of evolution lies. This is essentially the battle between saltationism and gradualism in embryo. So for PBS to claim evo-devo is a friend of Darwin is a little like Coriolanus embracing Aufidius. They are reluctant allies who would as soon stab one another except for the common enemy, the creationists.
Verdict: this is not even a pitch; it’s just Darwin fans rooting in the stands.
- Natural selection: “Evolution happens through natural selection,” the next entry states. We thought that was the question at issue. Ever hear of begging the question? This is no prediction; it assumes what needs to be proved. There it is, right before your eyes, a totally begged question, complete with another favorite D.P. quote that natural selection is “the greatest idea anyone ever had,” followed by a Big Lie by Niles Eldredge that nothing in 175 years has contravened it (even his own competing theory of punctuated equilibria?).
Verdict: this is a little dance on the pitcher’s mound getting applause from the Darwin fans again. No ball has been pitched yet. We’re getting impatient.
For rebuttals that show natural selection does not work as advertised, and has been essentially falsified, see 11/29/2004 and, more recently, 11/13/2007 and 10/17/2007.
- Galapagos finches: This was no prediction. Darwin found the finches while a creationist, then much later worked them into his evolutionary theory. But even if you allow a postdiction to count as a prediction, it is irrelevant, because even young-earth creationists allow for the microevolution seen in finch beaks.
Verdict: When are you going to pitch a ball, PBS? We want a pitcher, not a Lucy itcher. We’re starting to boo from the sidelines while the hysterical fans go ape.
- Genetics: Finally, a pitch. Darwin swings and misses. His theory of pangenesis was discredited almost as soon as it hit the shelves. He knew nothing of DNA, and did not predict anything like a code in the cell which, to him, was a simple blob of protoplasm.
Verdict: Strike one. For the Darwin party to give Charlie credit for DNA and molecular biology as a prediction of his theory is like giving Walt Whitman credit for the internet.
- Antisupernaturalism: What? That is the very question under consideration.
Verdict: Foul! Illegal procedure! This is no pitch; it is another egregious case of begging the question.
- Embryology: This is indistinguishable from #1. It’s evo-devo again. PBS failed to point out the Haeckel’s embryo hoax that sprang right out of Darwin’s own speculations. The shared genetic toolkit is no prediction of Darwin’s theory; it is an evidence that complex design was there from the beginning.
Verdict: No pitch. Sending the evo-devo clown out on the field for another cheer from the fans is a distraction.
- Sexual selection: OK, here’s a real pitch. Darwin did predict sexual selection would drive sexual dimorphism. (Actually, this is just another postdiction, because peacocks were already well known in his time.) The theory is controversial (02/26/2003), but at best, a peacock with radical tail feathers is still a peacock, not a new animal. Sexual selection does not explain the origin of new species.
Verdict: Ball One.
- Common ancestry: Ken Miller states, “Despite the extraordinary diversity of life, all living organisms share a nearly identical set of essential genes, reflecting their evolutionary development from a common ancestor.” Yet Darwin’s view was one not of “immortal” traits, nor of anything that has “survived essentially unchanged for over two billion years.” Darwin’s world is a fluid picture of gradual, incessant change, not stasis.
Verdict: More evo-devo. More begging the question. Common ancestry is the question under debate, not a prediction! They are not learning their lesson. This elicits a cheer from the fans in the stands, but no ball was pitched.
- Human evolution: “Humans evolved from an ape-like ancestor,” the next slide announces triumphantly, again begging the question. As support, the slide borrows an ancient 1863 Huxley drawing, and then repeats the discredited whopper that human and chimpanzee genes are 99% similar (see 06/29/2007). No fossil evidence is presented. They repeat Darwin’s speculation that “the difference between the mind of man and that of a chimpanzee or gorilla is a matter of degree, not of kind.” What did they do to interpolate this, interview Lucy or something? It’s not like creationists have failed to notice similarities and differences between humans and apes for thousands of years; so what has Charlie done to prove his condition that we evolved from them?
Verdict: Begged question, no evidence. Ball Two.
- Modern humans arose in Africa: Evidence is presented from phylogenetic trees and alleged hominid bones, most of which were found in Africa. This argument fails to recognize the selective effect of doing most of the digging in Africa, and the circular nature of finding Darwin trees in the genes, when unbiased analysis finds no tree (10/08/2007) and declares phylogenetic tree-building a function of assumptions (01/18/2006).
Verdict: the ball curves chaotically through the batter’s box, making any contact with the bat a matter of luck, not skill. Ball Three.
- Old earth: This was not a prediction of Darwin. Hutton, Lyell and other geologists had already decided long before The Origin to believe in an old earth, and they began interpreting the strata through that lens. Regardless of debates on the age of the earth, Darwin gets no credit for predicting it.
Verdict: Strike Two.
- Fossils: Precambrian fossils? Missing links? Gaps filled in with transitional forms? (see 10/15/2007 commentary on the PBS offerings, under numbered bullets #1). The gall of these people to use the most damaging evidence against Darwin’s theory as support for it!
Verdict: Strike Three.
- Moth tongue: OK, Charlie struck out, but we’ll entertain his final little just-so story, his lucky #13, as he walks to the dugout. He predicted a pollinator with a foot-long tongue would be found to pollinate a peculiar orchid, and by golly, one was found 40 years later. Awesome, dude. Cowabunga. Way to go. Ahem. The moth was still a moth, not some other animal, and the orchid was still an orchid. None of this is germane to the question of the origin of species. Since even young-earth creationists allow for dramatic variations of traits within kinds (look at dogs), this pitch is too little, too late.
Verdict: Don’t quit your day job, prognosticator. Go breed some pigeons. Be sure to use intelligent design.
So Charlie is out. He has failed to hit a single pitch from the list of predictions. He couldn’t even walk to first base, because the pitcher kept dancing on the mound.
We hate to hurt a guy’s feelings when he’s down, but must point out that even if he had struck a homer, it wouldn’t have mattered. You see, scientists and philosophers have known for a long time that predictability is no assurance of validity. There is an inherent logical fallacy in making and fulfilling predictions, called the fallacy of Affirming the Consequent (see Wikipedia for a convenient summary): “If P then Q; Q is true, therefore P is true.” This is a non-sequitur; there are other things than P that could have been the cause of Q. Example: Columbus told the natives that their gods were angry because of their treatment of his sailors, and were going to punish them by turning the moon blood-red. It happened! Columbus was good at predicting a lunar eclipse, but the natives believed the gods were angry, and treated him with much more respect. If you take a placebo because the experimenter tells you it will make you feel better, and you feel better, it doesn’t mean the placebo cured you. Astrologers and pseudoscientists for centuries have used this fallacy to their advantage.
The problem is even more serious at a deeper level. Philosophers of science since Pierre Duhem (late 19th century) have pointed out that theories are underdetermined by facts. No matter how many facts your theory can incorporate, or how many successful predictions it can make, there are always a nearly infinite number of other theories that could account for the phenomena. That’s why Popper proposed falsifiability as a criterion for good science. Many would argue that Darwinism has already been falsified, but then Popper is not the last word, either. Philosophy of science, the attempt to give a rational justification for scientific claims and discriminate good science from pseudoscience, has undergone multiple revolutions in the 20th century alone. There remains no consensus even today. All agree now, however, that the ability to make predictions is neither necessary nor sufficient to claim a theory is scientific. So even if Charlie had hit the ball, the game wasn’t valid in the first place. There is no joy in Dudville. Mighty Charlie has struck out. The officials, meanwhile, had already abrogated the game and declared it nugatory.