Facts and theory in Coyne’s “Why evolution is true”
“But if you believe that primates and guinea pigs [both of which have mutated, nonfunctional versions of a gene for making vitamin-C] were specially created, these facts don’t make sense. Why would a creator put a pathway for making vitamin C in all these species and then inactivate it? Wouldn’t it be easier simply to omit the pathway from the beginning? Why would the same inactivating mutation be present in all primates, and a different one in guinea pigs? Why would the sequences of the dead gene exactly mirror the pattern of resemblance predicted from the known ancestry of these species? And why do humans have thousands of pseudogenes [DNA sequences very similar to genes that are functional in other species, but with mutations that make them inactive] in the first place?” – Jerry Coyne, Why Evolution is True
I have been reading and enjoying “Why evolution is true”, by Jerry Coyne. Here are some thoughts on what I’ve read so far.
The preface struck one wrong note, I thought, stating that “evolution is far more than a ‘theory’…evolution is a fact.” This seemed to accept the popular definition of theory as wild speculation. In our 2003 paper, Strong Inference, The Way of Science (published in American Biology Teaher, vol. 65, p. 419), Tom Kinraide and I used a dictionary definition of theory: “The coherent set of hypothetical, conceptual, and pragmatic principles forming the general frame of reference for a field of inquiry.” Consistent with this definition, I would have said that “evolution is a theory (a set of explanatory principles) supported by thousands of facts.” Later in the book, Coyne has a good explanation of the difference between scientific and popular definitions of theory.
He explains evolutionary theory very well and presents a great selection of facts, all of which are explained by evolutionary theory but inconsistent with the religious claim that all species were created separately over a few days, only a few thousand years ago. There are other religious claims disproved by the facts, such as the claim made by fundamentalist Hawaiians that they are directly descended from taro plants – we are distant cousins, however, descended from a common ancestor -- but Coyne apparently sees Genesis literalists as the main threat to science education.
Kinraide and I also used a dictionary definition of fact: “An occurrence, quality, or relation the reality of which is manifest in experience or may be inferred with certainty.” We can infer with certainty that the earth is billions rather than thousands of years old and that humans and chimps are descended from a common ancestor who lived a few million years ago. Creationists might see the latter statement as the core of evolution, in which case evolution is indeed a fact, albeit an inferred fact. What evolutionary theory adds is explanations, answering questions like “how did that ancestral species split in two, and why are humans so much more intelligent than chimps?”
Here are a few of the manifest facts from as much of the book as I’ve read so far, and the inferred facts and/or theory to which they lead:
Manifest Fact: the facing coasts of Africa and South America match in shape, geological formations, and fossils. Satellite measurements show that the two continents are moving apart at about 6 cm per year. Inferred facts: the two continents were once joined and have been moving apart for millions of years. Six thousand years ago, when some fundamentalists think the earth was created, the two continents would have been only 180 meters closer together than they are today. Over longer time periods, the rate of movement might have changed, but a rough estimate is that Africa and South America separated about 100 million years ago (6000 km divided by 6 cm/yr). Contributions to theory: the earth is at least 100 million years old, old enough for significant evolutionary change to have happened. Also, if two related species live in Africa and South America today, ostriches and rheas, say, and their common ancestor lived long enough ago, their ancestors could have walked from one continent to the other without crossing an ocean (but see “The Elephant Bird’s Tale” in Richard Dawkin’s book, The Ancestors Tale for some complications!).
Manifest Facts: changes in coral growth over a day and over a year produce corresponding “growth rings.” Corals alive today have 365 day rings per year ring, but some fossil corals have more day rings per year ring. Astronomers have measured the speed of rotation of the earth and found that it is slowing slightly each year. Inferred facts: days would have been shorter in the past, resulting in more days per year. If we use growth rings to calculate how long ago a certain fossil coral lived, we get the same answer as from radioisotope dating: 380 million years (Nature vol.197, p. 948). The earth is much older than fundamentalists believe. Contribution to theory: radioisotope dating is accurate enough to be useful in dating rocks associated with fossils.
Manifest Facts: modern whales have tiny bones, not connected to anything, about where their rear legs would be, if they had them (visit a natural history museum and see for yourself!). The fossil species Dorudon, dated to 40 million years ago (MYA), resembled whales, but smaller, with recognizable rear legs too small to do much of anything. Fossil species Rodhocetus, from 47 MYA, was even smaller, with rear legs extending backwards like flippers. 50 MYA was Ambulocetus, with legs long and strong enough to walk awkwardly on land or more easily in water, like a hippo. Before that (52 MYA) lived Pakicetus, smaller still and with longer legs. This series of fossils, all from the same area, also differs progressively in the position of the nostrils, with the most recent fossil, Dorudon having them farthest back, a whale-like blow-hole. Inferred facts: whales evolved from smaller mammals that spent a lot of time in water, with much of the change in size and shape occurring over a 10-million year period. Contribution to theory: ten million years (much less than the minimum ages for the earth inferred above) is plenty of time for major evolutionary change. So, for example, we don’t need to doubt molecular and fossil evidence that the common ancestor of humans and chimps lived only about six million years ago.
Manifest facts: Coyne recommends two evolution blogs, Laelaps, which recently discussed evolution of whales, and This Week in Evolution. He also states that I am a professor at Cornell. I earned my Ph.D. there, in Crop Science, but have been a professor only at UC Davis and here (as an adjunct following my wife) at the University of Minnesota. Inferred fact: Coyne is unusually insightful, but there may be a few minor errors in his book! Contribution to theory: it is difficult to write a full-length book without making a few minor errors. That may be some consolation as I work on Darwinian Agriculture. I missed my April 1 deadline, but Princeton University Press kindly gave me another six months.