Examining the Evidence for Evolution
It would take a much longer book than the one I’m writing to examine all of the evidence concerning evolution. No individual person could do so much as read about (much less evaluate) all of the relevant research in genetics, biochemistry, paleontology, and so on. Nevertheless, it will be worthwhile to consider six major types of evidence that are frequently cited in support of the theory of evolution, and also to consider some of the objections critics have raised against each type of evidence.
Before proceeding, readers may find it helpful to know where I stand on this issue so that you can better discern the biases and presuppositions I might inadvertently bring into the discussion. Before examining the various types of evidence, then, let me offer a few brief remarks about my own perspective. In my judgment, there is substantial evidence for each of the two central theses of evolutionary theory mentioned at the beginning of this chapter; and I also believe, for reasons explained in the next chapter, that these theses do not necessarily contradict what the Bible teaches about creation. On the other hand, however, I am far from certain that the central theses of evolution are true. Moreover, I am not convinced that evolutionary science has already provided a complete and satisfactory explanation even for the diversity of species, let alone for the origin of the first living creatures, the astonishing intricacy of biochemical machinery, the unique characteristics of humankind, or the marvelous beauty of the living world. Many important, foundational puzzles remain unsolved, as we will see. Perhaps, someday, these problems will be resolved within the framework of current evolutionary theories and models; or perhaps a significant “paradigm shift”The concept of a scientific “paradigm” will be discussed in the last chapter. will be required.
Thus, to summarize my position: I do not know to what extent God employed natural processes and mechanisms, as opposed to supernatural miracles, in his creative work. (Frankly, I’m not even sure that there is a sharp distinction between natural and miraculous processes.Christian theologians often distinguish between special and general divine action. General divine action refers to God’s continual activity in sustaining the laws and regularities of nature, while special divine action refers to God’s activity in bringing about a specific event that would not ordinarily occur in the course of nature. For example, general divine action occurs when “He causes his sun to rise on the evil and the good, and sends rain on the righteous and the unrighteous” (Matthew 5:45, NIV). Special divine action occurs when Jesus walks on water (Matthew 14:25) or raises Lazarus to life (John 11:43). Aside from such paradigmatic examples, however, there are many instances in which the line between special and general divine action cannot be drawn so sharply, and the distinction between natural and miraculous is blurred. When God “directed an east wind” to bring locusts into the land of Egypt (Exodus 10:13), should we regard that as a miraculous event or a natural one?
The precise relationship between God’s sovereign providence and the regularities of nature has been a topic of debate among theologians since the time of the early church, and a complete grasp of this relationship probably exceeds the limits of human comprehension. Though I find many possibilities plausible, my best guess (for what it’s worth) is that God continually sustains and guides the workings of nature at the fundamental “quantum” level—or perhaps at an even deeper, as yet undiscovered level—so that events which seem fundamentally chancy or random (e.g. quantum collapse, radioactive decay, etc.) are in fact subject to His guiding hand. Christian philosopher Alvin Plantinga considers a specific possibility along these lines in chapter 4 of his excellent book Where the Conflict Really Lies: Science, Religion, and Naturalism (New York: Oxford University Press, 2011). Supposing the GRW interpretation of quantum mechanics is correct, Plantinga suggests, God might influence or even determine the outcomes of the collapse events which constantly occur at the microphysical level, thereby actively steering the course of nature without contravening the fundamental quantum laws. If something like that turns out to be the case, then there may be no sharp distinction between miracles (understood as God’s supernatural “intervention” in nature) and the seemingly non-miraculous operation of ordinary physical processes, which likewise are manifestations of divine activity in the world.) The problem isn’t that I see no way to reconcile science with scripture. Rather, the problem is exactly the opposite. There are too many plausible ways to fit the scientific evidence together with Biblical revelation, and I don’t know which of the many alternatives is correct!
We’ll consider a variety of Christian perspectives in the next chapter, where I’ll share my own opinions in more detail. For now, I want to emphasize that there is plenty of room for Christians to disagree about the interpretation of scientific evidence, just as we may disagree about the interpretation of Scripture. (For further reflection on this point, see my review of the book How I Changed my Mind about Evolution: Evangelicals Reflect on Faith and Science, edited by Kathryn Applegate and J. B. Stump.) For this reason, although I have my own opinions, I will do my best to present the arguments on both sides of each issue as impartially as I can, so that you may weigh the evidence and judge for yourself what is true. I’ll focus on the scientific arguments here; arguments concerning the interpretation of Genesis and other relevant biblical passages will be considered in the next chapter. With that disclaimer and promissory note out of the way, let’s consider the major categories of evidence for the modern theory of evolution:
- Evidence from observed cases
- Evidence for evolutionary mechanisms
- Evidence from biogeography
- Evidence from homology
- Evidence from genetics
- Evidence from paleontology
These six categories will be outlined in the following sections, where I will also provide a brief summary of common objections to each type of evidence.
Evidence from observed cases
There are documented historical cases of biological evolution occurring, in small degrees, even within the past few centuries. Many types of bacteria have developed resistance to antibiotics over the past several decades, for example, as a result of mutation and natural selection. Moreover, careful experiments have been conducted with bacteria, fruit flies, and other organisms that reproduce quickly, in order to study how evolution occurs over many generations. One important study is the ongoing Long Term Evolution Experiment led by biologist Richard Lenski. Since the experiment began in 1988, Lenski and his team have tracked the lineages of 12 initially identical E. coli bacteria over 75,000 generations. Modest changes due to mutation and natural selection have been observed, and although the significance of these findings is often exaggerated in popular media, experiments like these do lend plausibility to some crucial aspects of evolutionary theory.
In response to this type of evidence, critics point out that all observed cases are examples of microevolution (small variations in pre-existing organs and structures) as opposed to macroevolution (the emergence of entirely new organs or structures). Many opponents of the theory of evolution, including some young-earth creationists, readily concede that microevolution occurs; but they deny that this fact is compelling evidence that macroevolution has also occurred. Even some mainstream proponents of evolutionary science are critical of the extrapolation from microevolution to macroevolution.See, for example, Douglas H. Erwin, “Macroevolution Is More than Repeated Rounds of Microevolution,” Evolution and Development 2, no. 2 (March 2000): 78–84. For additional examples and further discussion of this point, see Michael Denton, Evolution: Still a Theory in Crisis (Seattle: Discovery Institute Press, 2016), 24-25; also Stephen C. Meyer, Darwin’s Doubt: The Explosive Origin of Animal Life and the Case for Intelligent Design (New York: HarperOne, 2013), 314.
One reason why microevolution might not be persuasive evidence for macroevolution is that the latter requires the production of novel genes and gene-regulatory networks, whereas microevolution can be explained by relatively minor mutations in existing genes or by the recombination of pre-existing alleles. No observed case of microevolution has ever produced an entirely new functional gene, much less a new gene-regulatory network.Mutations have been known to adapt existing genes to new functions, however. For example, certain bacteria have evolved an enzyme that can digest nylon, which was only invented in the 1930s. The enzyme in question, called nylonase, initially was thought to have originated from a frameshift mutation, which would have been an unequivocal case of a novel protein-coding gene evolving in recent history. As it turns out, though, nylonase originated from relatively minor mutations in a pre-existing functional enzyme.See this article for further discussion of the nylonase story.This isn’t necessarily a problem for evolutionary theory, since such changes presumably happen too infrequently or too slowly for direct observation. However, the fact that we haven’t observed the production of new functional genes or GRNs means that a simple extrapolation from observed cases of microevolution is unwarranted.
Another reason to be skeptical of the inference from microevolution to macroevolution is the fact that observed microevolutionary adaptations often involve a loss of genetic information. For example, in the Long Term Evolution Experiment mentioned above, one of the twelve lineages of E. coli bacteria evolved the ability to metabolize an additional food source in the nutrient solution that had been provided for them. However, careful analysis of the genetic mutations in these bacteria revealed that their new ability was the result of a broken gene, not a novel gene.See this article for a detailed explanation. Similarly, a number of well-documented mutations that confer resistance to malaria in human beings involve broken or damaged genes, which often lead to other diseases such as thalassemia and sickle-cell anemia.For details and further discussion, see Michael J. Behe, Darwin Devolves: The New Science About DNA That Challenges Evolution (New York: HarperCollins, 2019), 181-187. Thus, although these mutations may be beneficial in a specific environment (where malaria-ridden mosquitos are prevalent), they can hardly be regarded as stepping-stones in a macroevolutionary transition.
As these examples illustrate, mutations usually are destructive in the sense that they impair or disable genes rather than introducing functional new genes; and even beneficial mutations typically involve either a loss of genetic information or the duplication of pre-existing genes. Mainstream proponents of evolutionary theory acknowledge this point. However, they argue, it is plausible that mutations are occasionally constructive, introducing new genes that are actually useful. This brings us to a second type of evidence, which will be the topic of the next section: evidence for plausible mechanisms of evolution.