Since I have not had any success in finding a book that presents the best arguments of both evolution and creationism side by side, without trying to convince the reader one way or the other, I finally decided I’d just have to work at assembling the information I wanted myself. Back in January, I read in the Wall Street Journalabout Jerry Coyne’s new book, Why Evolution is True. I checked for its availability through inter-library loan, and somewhat to my surprise a copy had already been purchased, and it was soon in my hands.
It has taken me over a month to finish, reading usually just part of a chapter a night, but it’s been very interesting reading. The writing is clear and easy to understand, as it is written for the average person with no special training in biology. I’ve made notes for myself to refer back to later, so I can take a closer look at the creationist objections to Jerry Coyne’s arguments for evolution.
Simply reading the book, without any resources on hand to check what he says, I would say Coyne makes a convincing case. I assume that creationist objections would have to include asserting that Coyne misstates facts, leaves out evidence that would weaken his arguments, or otherwise misleads the reader to think that his cases is stronger than it is. The only obvious flaws in the book, in my mind, are in his dismissive attitude towards those who do not accept his views.
From the beginning, in the Preface and Introduction, Coyne makes it clear that he is out to show that evolution is, beyond any doubt, most definitely true. Since the title of the book indicates that right on the cover, I found his repetitions of this point annoying, especially as he had not yet gotten to the point of showing how or why it is true.
Since he is writing for those open to what he has to say (he states plainly that he knows he won’t convince someone who, for religious reasons, is certain that evolution is false), I’m not sure why Coyne thinks he needs to hammer that point so often. Show the evidence, give the explanations, and let people be convinced, or not. Repeating over and over that your thesis is true is not a very good way of convincing anyone, and only seems to highlight the opposition that he knows there will be to everything he says.
Once past the introduction, Coyne launches into a basic primer on evolution, summarizing it thus:
Life on earth evolved gradually beginning with one primitive species – perhaps a self-replicating molecule – that lived more than 3.5 billion years ago; it then branched out over time, throwing off many new and diverse species; and the mechanism for most (but not all) of evolutionary change is natural selection.
He then discusses six concepts contained in that definition: evolution (genetic change over time), gradualism (change requiring many generations), speciation, common ancestry, natural selection, and non-selective mechanisms for evolutionary change.
These concepts are often lumped together, and I appreciated his separating them out. I know that creationists, for instance, realize that natural selection does work to favor some features over others – for instance, coloring that allows a creature to blend in with its surroundings and thus escape notice by predators. Where they disagree is whether this can result in the creation of new species, or simply change how common certain features are within one species.
In order for one species to give rise to another, mutations have to take place to change the genetic blueprint. Mutations do occasionally take place, we know; the questions are whether mutations can be beneficial, and whether enough (beneficial) mutations can accumulate to result in a new species. Coynewill deal with the first question later in the book, but he asserts that the fossil record is ample evidence that such changes have in fact taken place.
This is the area where I have probably heard the most counterarguments, usually questioning the validity of the dating methods used. Coyne does not spend a great deal of time going into detail on this, but he explains that there are different isotopes that decay at different rates, and dates calculated using different isotopes agree with each other. Moreover, those that are recent enough for carbon-14 dating to be used also agree with the dates determined in that manner. There are other dating methods as well, one of which uses fossil corals, and it also confirms the accuracy of radiometric dating.
If the dating methods are accurate, and fossils have in fact been found in the sequence stated, going from simple one-celled marine animals in the oldest strata (I was surprised to learn that such tiny fossils could even be detected) to more and more advanced animals, with the most recent strata containing animals most similar to living animals today, that certainly fits well with the teaching on evolution. It doesn’t prove that evolution happened, of course, but one would wonder why the fossils would be arranged that way otherwise.
The chapter on embryology was interesting, but less convincing. I had read long ago how at early stages of development, a mammal has features reminiscent of a fish. What was new to me was to learn of different types of kidneys that are developed in humans and then discarded before the final kidneys are developed, blood vessels that move around or disappear during development, and nerves that follow a pattern that works well for fish but in humans is more prone to injury.
Also new to me was the explanation. We learned in 10th grade biology about embryos showing evidence of evolution, but if Mr. Mildrum ever explained why it would be that way I don’t remember it. Coyneexplains that evolutions works by making tiny changes that are just good enough to give a reproductive advantage (survival only matters to the extent that it results in reproducing more). So changes are always based on the previous “model,” including all of its features plus whatever is new. The fully developed animal may have very different features, but the development of the embryo starts with the ancestor’s path of development and then modifies it further.
The chapter on geography was less interesting to me. If evolution takes place, it makes sense that animals living in one area would be most similar to animals living in a contiguous region, and also to extinct animals in the same area. But divine creation can equally well explain similar animals in a similar habitat, since they would need to deal with pretymuch the same kind of environment (as there are rarely contiguous areas with radically different climate, flora, and fauna). What I was still waiting for Coyneto deal with was the issue of how the evolutionary changes actually take place.
The following chapter, on natural selection, finally gets to the heart of the matter. This was Darwin’s big contribution to the theory, as many people had already suspected that evolution had taken place but did not have an explanation of how it worked. Darwin was mistaken on the actual mechanism of inheritance (just the other day in a doctor’s waiting room I read in National Geographic how Gregor Mendel published his work 7 years after Darwin published The Origin of Species, but no one took much notice of it until decades later). Yet Darwin identified natural selection as the process by which organisms inheriting the characteristics that made them fitter (not necessarily fittest) would have the best opportunity to pass on those same characteristics to their descendants.
In order to become fitter, though, in a way that could be passed on, some genetic change had to take place. This means mutations, and creationists are quick to argue that mutations are nearly always harmful. What surprised me is that Coyne acknowledges this as true (actually he says that most are either harmful or neutral). He points out, however, that this hardly invalidates the idea of evolution.
All those mutations that are harmful represent genes that will not get passed on, at least not very far. The neutral ones (where the change neither helps nor hurts the organism) will get passed on but will have no great effect. But those few mutations that do prove beneficial will survive, and over time out-survive others of the same species without the mutation. It will take a very long time, but over time those few beneficial mutations will add up, and eventually result in an organism different enough from its ancestors to be considered another species.
Two objections that I am familiar with are generally raised at this point. First, whether there is enough time for those slow changes to result in the wild diversity of life as we know it today (even if one does allow the possibility that it could change). Second, whether there is evidence that the new features were not after all contained in the genes of the ancestor.
Regarding the first question, Coyne says that there are about 10 million species alive today. Since scientists are still discovering many species (I have been reading on National Geographic’s website recently about the many new species being identified in Australia), Coyneraised that number to 100 million. Since the number of species could increase exponentially (a single species can divide into two, those two into four, then eight, sixteen, thirty-two, etc.), if you started with a single species 3.5 billion years ago (the earth is estimated to be about 4.6 billion years old), and easily reach 100 million species today.
That is assuming a rate of each species splitting into two new species only once every 200 million years. Speciation is thought to actually take place considerably faster. In the case of the fruit flies that Coyne and his colleague studied, they estimated that it took about 2.7 million years for two species to have diverged completely from their common ancestor. In cases where polyploidy takes place, it can happen quickly enough for humans to actually observe new species developing.
As to the second point, the creationist will claim that the ancestor’s genes contain all the possible variations that will later be seen. Rather than new features being added in its descendants through mutation, some of the genetic information is lost so that the descendant’s features are more fixed and it can no longer produce offspring with rather different features. Other descendants of the original ancestor may have lost different information so that they come out with a different set of features. But, according to this view (as I understand it), any feature an animal has today must have been encoded in the genes of that ancient ancestor.
I did not see this addressed directly in Coyne’s book. (If it was there I missed it.) But I took a quick look on the internet while writing this and found a site that specifically addresses this point. Part of Defender’s Guide to Science and Creationism, it explains that “individual organisms can have at most two alleles for each gene locus,” so that a single pair of animals can have only four alleles (for each gene locus) between them. Since, according to the Genesis account of Noah’s ark, for most kinds of animals there were only a single pair to repopulate the earth, there would be no more than those four alleles in their descendants today – apart from mutations. For most organisms today, however, we do find far more than four alleles per locus.
It’s been too long since I took high school biology for me to remember quite what a gene locus refers to, but I get the idea regarding the alleles (different forms of a gene). Vuletic gives the example of one of the genes in the human leukocyte antigen complex, which has 59 alleles. If we are all descended from Adam and Eve, he points out, mutation must have taken place to produce those 55 additional alleles.
What interested me more was his next point. Is there evidence of an organism that clearly lacks a particular feature, whose descendants have it?
Joshua Lederberg did an experiment in which he grew thousands of colonies of genetically identical bacteria from a single bacterial cell that was unable to survive in the presence of streptomycin. He divided each colony of cells in two, and grew one half with and one half without streptomycin. A few of the colonies survived on streptomycin, because they carried new mutations for streptomycin resistance. (Futuyma 1983:137)
Since the bacterium from which the resistant colonies evolved was not itself streptomycin resistant, Lederberg’s experiment proves that such resistance is the result of one or more mutations.
That seems convincing to me. I suppose someone might argue that the original bacteria could have had the genes for resistance but that the genes were “turned off” in some way. I don’t know enough of the science involved to know if that is a possibility.
Proponents of Intelligent Design argue that while natural selection would favor organisms with certain characteristics, there are characteristics that could not come about by chance (through a series of mutations) to be selected for. Coyne admits that there is no way biologists can figure out how every characteristic developed, but he says this is not necessary. It is only necessary, he says, to show how the development is feasible, based on our growing understanding of biochemistry. Regarding a specific example which ID claims is too complex to have evolved – blood clotting in vertebrates – Coyne says that two biologists have already “worked out a plausible and adaptive sequence for the evolution of the entire blood-clotting cascade from parts of precursor proteins.”
Besides showing how such characteristics could have developed step-by-step, proponents of evolution also have to be able to account for how natural selection would favor those animals that are only part way through developing such complex features. Using the eye as an example, Coyne describes how a simple light-sensitive patch of cells would help a simple organism survive, and subsequent improvements could, over time, lead to a complex eye.
A mathematical model used by researchers in Sweden simulated the random changes to the tissue around the simple light-sensitive cells, discarding unhelpful mutations and accepting beneficial ones. In 1,829 tiny steps, something similar to the vertebrate eye developed. Using conservative assumptions regarding the length of time required (so that the estimate should be longer than the actual time required), they estimated that it would have taken 400,000 years. This fits easily within the time frame mapped out by evolutionary scientists.
I found the next chapter, on sexual reproduction, very interesting, particularly as virtually all of the material was new to me. I had seen (on worldmagblog) references to evolution not being able to explain sexual reproduction, but had never seen a discussion of the matter to know what the issue was. I’m still not sure how well I could explain it, but basically it says that an organism using asexual reproduction can pass its genes on 100%, while using sexual reproduction only passes on 50%, with 50% coming from its mate. So asexual reproduction would seem to be the most efficient way to pass on the best genes.
Evolutionary biologists assume there must be an advantage to sexual reproduction, that more than outweighs the disadvantages. They just haven’t figured out what it is yet. Likewise, there are many adaptations of males of various species, that seem to be purely to attract females, but that carry with them distinct disadvantages (bright colors that makes them easy to spot by predators, various enlarged features that use the body’s resources to develop and sustain). These disadvantages are assumed to be outweighed by the greater reproductive capacity that these males get by attracting more of the females.
The chapter on speciation (the origin of new species) is harder to summarize, as it gives so many examples of ways in which new species arise. Usually it is the result of geographic separation, where animals (or plants) of a single species end up in two distinct areas (due to a physical barrier of some type such as a mountain or river, or to great distance from having wandered or been carried far away). Within a single population, whatever genetic changes take place are spread throughout the population. But in two separated populations, different changes may take place, enough so that eventually even if they meet up again they will no longer interbreed (due to physical incompatibility, lack of attraction to each other, or their offspring being sterile).
The discussion of human evolution had some interesting points, but a lot of it was familiar to me, and a single chapter is too short to do the subject justice. I have read objections that supposed transitional species – between humans and their common ancestor with other great apes – are often identified based on only a few parts of a fossil skeleton. Coyne discusses the discovery of “Lucy,” an Australopithecus afarensis, who he says is apelike from the neck up, almost modern human from the waist down, and a mixture in the middle. He says that her skeleton was discovered in hundreds of fragments, but he does not say how it was determined that they all came from a single individual. I’m sure some skeptics regarding evolution would suggest that what was found was a mix of some human bones with some from an ape.
The final chapter tries to address concerns that teaching evolution is bad because it destroys any basis for morals or finding meaning in life. Even those who think that overall Coyne has done an excellent job with this book admit that this chapter is weak. Perhaps this is because at this point Coyne is dealing more with personal opinions than science. After all, his expertise is in genetics, not philosophy. The essence of what he says here can be seen in these sentences:
There is no reason, then, to see ourselves as marionettes dancing on the strings of evolution. Yes, certain parts of our behavior may be genetically encoded, installed by natural selection in our savanna-dwelling ancestors. But genes aren’t destiny. One lesson that all geneticists known, but which doesn’t seem to have permeated the consciousness of nonscientists, is that “genetic” does not mean “unchangeable.”
So, Coyne says, we make our own meaning and our own morality. This may satisfy some people, but to many creationists will just be more evidence of the danger of evolution’s teachings, leading people away from any sense of moral absolutes to a relativism where almost anything can be justified if it is “meaningful” to someone.
There are other ways that Coyne’s arguments seem to reveal a lack of understanding of the creationist perspective. In several different discussions, he points out a pattern that is explained by evolution but not by creation. Why, he asks, would a Creator distribute animals according to this pattern (that evolution explains) or why would a Creator give creatures non-functional genes? (There are other examples – those are the first two that came to mind.)
To Coyne, this seems to be an argument against creationism. But the believer in creation can simply point out that there is a great deal that we don’t know yet. Future discoveries may well explain a pattern that right now seems purely arbitrary. And there will always be some things we don’t understand, because God’s understanding is infinitely greater than ours, and He is under no obligation to explain everything to us. An evolutionary explanation that gives reasons that make sense to us may be more appealing, but that hardly constitutes proof that it is actually the true explanation.
But Coyne spends little time directly addressing creationists. He primarily explains the basics of evolution as it is understood today (advanced in our understanding of genetics have changed the field a good deal since Darwin’s time), and for understanding that it is a good book to read.