Wednesday, May 26, 2010

Evolution's Gaps versus Creationism's

We are all connected.

I recently had a conversation in which I was taken to task for talking about evolution as if it were a fact. My excuse, of course, is that evolution is very well attested. I agree with the scholarly consensus that asserts evolution rises to the level of fact. In our exchange, my conversational partner reminded me that "there are huge gaps in evolution." I may agree with the proposition of there being gaps, however large, in evolution, and I probably should have articulated my opinions on evolution with greater humility.

Nevertheless, I've been thinking about the premise that evolution has huge gaps. From this initial premise, the reasoning usually proceeds to then state that the huge gaps mean the figurative jury is still out on evolution. Therefore, if evolution remains an unresolved question, then one is justified to maintain his or her preferred religious beliefs--in particular, one may comfortably hold onto the doctrine that people were created by God. One assumption running around in this reasoning is that evolution contradicts the teachings of the Bible, so if evolution is accurate, then the teachings of the Bible are false. The resulting implication, then, is that if this one core teaching of the Bible is false, then every other teaching that follows is similarly suspect and open to question.

I want to talk here about the "gaps" reasoning by looking at the theory of evolution and how a gaps charge against it is made. My intention is to show that the charge isn't very strong and to conclude finally with some thoughts on the implications for the Bible's teachings.

Let me declare up front that I have no training at all in the biological sciences beyond high school and my own reading on the subject. I will not, therefore, try to champion or to explain the scientific merits of evolution. What I would like to do, however, is present some of the key claims or hypotheses of evolution and then relate what I see.

To start, let's take a definition of evolution from the University of California, Berkeley:
The definition
Biological evolution, simply put, is descent with modification. This definition encompasses small-scale evolution (changes in gene frequency in a population from one generation to the next) and large-scale evolution (the descent of different species from a common ancestor over many generations). Evolution helps us to understand the history of life.

The explanation
Biological evolution is not simply a matter of change over time. Lots of things change over time: trees lose their leaves, mountain ranges rise and erode, but they aren't examples of biological evolution because they don't involve descent through genetic inheritance.

The central idea of biological evolution is that all life on Earth shares a common ancestor, just as you and your cousins share a common grandmother.

Through the process of descent with modification, the common ancestor of life on Earth gave rise to the fantastic diversity that we see documented in the fossil record and around us today. Evolution means that we're all distant cousins: humans and oak trees, hummingbirds and whales.
What strikes me immediately is the elegance of the definition and what it purports to explain. The theory is really quite simple and very beautiful, which of course is not a reason to think it's accurate or wrongheaded. For me, the strength of the theory lies in its specificity: gene frequencies, populations, generations, species. It tells me that I can look at gene frequencies across populations, generations, and species to confirm or to falsify the central idea of common ancestry.

What, then, are the sources of evidence for evolution? According to the same website, the main sources include:
  • Fossil evidence -- Most commonly, an organism, a physical part of an organism, or an imprint of an organism that has been preserved from ancient times in rock, amber, or by some other means. New techniques have also revealed the existence of cellular and molecular fossils.
  • Homologies -- Similarities between related organisms in anatomical, molecular or cellular features.
  • Distribution in space and time -- Dating of fossils and elements, and population patterns of living things across all the Earth.
  • Evidence by example -- Present-day organisms and recent history as sources of information about the past. Artificial selection, experiments, and nested hierarchies all provide additional information that sheds light on the development of life forms.
With the definition of evolution and identification of the main sources of evidence for evolution, we have a rudimentary sense of what evolution is and how we know what we know about it. The third and final element of evolution that I want to introduce is how evolution works, the mechanisms that drive the modifications in "descent with modification."

I like the explanation given by doctoral student Jeremy Yoder, who describes the "Big Four" processes of population genetics:
These are the four processes that account, in one way or another, for every change in the frequency of genes within natural populations. In other words, the Big Four account for much of evolution itself. They are:
  • Natural selection, changes in gene frequencies due to fitness advantages, or disadvantages, associated with different genes.
  • Mutation, the source of new forms of genes;
  • Genetic drift, or changes in gene frequencies that arise from the way probability works in finite populations; and
  • Migration, or changes in gene frequencies due to the movement of organisms from site to site.
Lay readers may be surprised both by what we know, and what we don't, about how these four processes operate in nature. Natural selection is relatively easy to measure, and apparently ubiquitous in natural populations—but we don't know how often the resulting short-term changes impact evolution over millions of years. Mutation, the source of variation on which natural selection acts, seems to vary widely among living things. Genetic drift means that a trait can come to dominate a population even if it has no fitness effect—or sometimes a deleterious one. Finally, migration across variable landscapes can interact with selection, drift, and mutation to completely alter their effects.
I highly recommend Yoder's series of blogs on the Big Four, and his blog is quite excellent generally.

Although I think we have here a pretty good sketch of what we're talking about when we talk about evolution, I also want to devote some time and space to the idea of the "gaps" in evolution. Let me say up front that I have no doubt that there probably are "gaps," if that means unknown or unresolved elements in our picture of the historical origins and development of particular species. I don't have a problem with gaps in principle because there are a lot of species on Earth (5 to 100 million; science has identified 2 million) and there's a huge amount of time to work with. The Earth may be about 4.6 billion years old, and "[i]t is estimated that the first life forms on earth were primitive, one-celled creatures that appeared about 3 billion years ago" ( I don't expect minute-by-minute accounts of the development of every single population on Earth going back 3 billion years.

However, I do expect that some elements of evolutionary theory--its central claims, lines of evidence, identified processes, and the relationship between them all--would receive careful scrutiny from scientific experts and laypeople alike. Here, for example, is a description by an organization called Answers in Genesis that discusses "Gaps in the Fossil Record":
The most glaring problem with the belief that all life arose from a common ancestor is the lack of fossil evidence of the millions of transitional forms that should be evident if evolution had happened.

It must be noted that this argument is often dismissed through two lines of reasoning: 1) the lack of a complete fossil record and 2) the problems inherent in identifying what is transitional. However, this does not diminish the problem, as some evolutionists suppose, since the types of changes evolution requires to give rise to the various animal kinds over millions of years would be expected to provide ample examples in virtually every layer of the geologic record. This is not the case.

Instead, most of the geologic record is better explained by the catastrophic processes during the global Flood and the subsequent localized catastrophes after the Flood (e.g., that formed the Grand Canyon).
I must say that the above passage is rather offensive because it is quite flagrantly using rhetoric and emotional language to muddy what might be a real argument. The first paragraph frames the question about the fossil record as a "problem," and a "glaring" one at that. It also characterizes (misleadingly, I would say) the hypothesis of common ancestry as a "belief." I see this particular case as an instance of trying to equate a belief derived from scientific method with one derived from traditional teachings. The first emerges as a conclusion based on observable facts, study, and experimentation. the second emerges as a sense of intellectual satisfaction based on received stories, dialogues, and personal experience. My point is, however, that before we get to the real substance of the "gaps" challenge, the writer or authorizing agent of the challenge is trying to cheat by framing the matter as one of traditional belief.

But what of the substance of the "gaps" challenge? The basic objection is the hypothesis that if evolution had happened, then there should be millions of fossils corresponding to "transitional forms." What are transitional forms? According to the International Society for Complexity, Information, and Design, a transitional form is:
An organism with features that it holds in common with organisms presumed to be its ancestor and descendant but that neither of these hold in common. For instance, archaeopteryx has feathers in common with birds and scales in common with reptiles, but neither of these features belong to both birds and reptiles.
A second definition comes from the UCal Berkeley site:
Fossils or organisms that show the transformation from an ancestral form to descendant species' form. For example, there is a well-documented fossil record of transitional forms for the evolution of whales from their amphibious ancestor.

So, the Answers in Genesis charge is that there are more gaps in the fossil record than we should expect. With the caveats that I'm not a biologist and not familiar with all of the evidence that we actually do or don't have for evolution, I must say that I'm not impressed with AiG's charge. My main reason for this, however, is logical: I would expect the common ancestry hypothesis to be based on the fossils that we have, not the ones we don't have. I would also expect that the fossils we have fit with the other sources of evidence. I'm not terribly concerned about missing fossils because of the number of species and the vast amount of time involved. If the two definitions above of transitional forms can be trusted, then we have at least two examples of transitional forms, so we know that in some cases we can see it. I would like to know why we wouldn't see it in other populations and species over time.

I also don't find the final paragraph of the AiG charge as helpful as it could be. There, a counter hypothesis is made that "most of the geologic record is better explained by the catastrophic processes during the global Flood and the subsequent localized catastrophes after the Flood (e.g., that formed the Grand Canyon)."

First, it seems to me that we have abruptly switched gears. In evolution, fossils are one source of evidence. The fossil record shows evolution over time. In the AiG formulation, however, fossils are not a source of evidence but instead the thing to be explained. Could the location of particular fossils be the result of certain catastrophes? Why yes, I don't see why not. But catastrophism does not tell us anything about the relationship of different fossil specimens to one another, if there is a relationship.

This is the second element that makes the AiG charge unhelpful for me: the lack of a coherent formulation of the hypothesis set up as the alternate to evolution. Combining the explanation of evolution given before and the AiG charge given above, I imagine that the alternate hypothesis is:
Through the catastrophic processes during the global Flood and the subsequent localized catastrophes after the Flood, God made life on Earth and gave rise to the fantastic diversity that we see documented in the fossil record and around us today.
If this is an accurate representation of the special creation hypothesis, or at least a part of it, then I think it's clearly weaker than the descent with modification hypothesis. Why? Because the hypothesis will not work if

(1) We don't have positive evidence of a worldwide deluge.
(2) We don't have positive evidence of [a] God.
(3) We cannot explain what it means to use a term like "made" in the context of life formation.

I imagine a real biologist could comment much more effectively on the relative weakness of the alternate hypothesis, but I think the point can safely be made that Occam's razor applies here and we are right to approach the alternate hypothesis with extreme skepticism.

I also imagine that my conversational partner meant more than the fossil record by "huge gaps" in evolution. I won't make any guesses as to what that might mean, but I'm already not predisposed to going through another AiG-type exercise where the objection to evolution is framed misleadingly, where the objection is of seemingly minor significance, and where the alternate hypothesis actually broadens the number and scope of items to be explained.

In sum, the difference between the definition of evolution and the alternate hypothesis is that the first gives a way to solve a problem while the second one gives more problems. The descent with modification hypothesis may ultimately fail, but the hypothesis itself articulates how to go about reinforcing or falsifying it. The special creation hypothesis is less clear in its articulation and depends on unestablished categories such as global Flood and God.

When we compare evolution to creationism, then, we can fairly conclude that

Whatever the gaps in evolution, the gaps in creationism are substantially bigger and badder.

Indeed, this conclusion seems to me so obviously sensible and accurate that I really wonder why anyone would prefer creationism to evolution. Can someone explain that to me?

I'll answer my own question by returning to the idea of biblical teachings. When a believer talks about biblical teachings, the matter includes both the substance of the story told and the "lessons," the articulation of right behavior derived from the story. The matter also includes doctrinal matters, such as teachings around the "Fall," sin, afterlife, and so forth, but I am not really concerned with doctrine.

Let's say, for instance, a church teaches that the biblical story of creation, particularly the creation of humankind, implies that each person is special and valuable to God. What happens to this teaching if the story is not true? My answer is that it does not necessarily make all of the teaching untrue. The essential lesson on human specialness and value can remain intact. Specialness and value, however, become re-contextualized: humans as special against other people and other living things (which are also special), and as valuable in reference to the family and societies to which people belong.

This post is already too long, so I may continue on the above line of thinking in a separate essay, but my point here is only that evolution contradicts the factual/historical/scientific claims of the creationist's Bible. It challenges some elements of the Bible's moral teachings but allows for the core of the teachings to retain their fullest expression.


  1. Anonymous2:34 PM

    The evidence for an event happening in the past is always going to be less than what we personally experience

  2. Really? Please explain.

    Suppose a person sneaks up from behind, knocks me out, and then robs me by taking my wallet.

    Later the police find the person, with the implement and the wallet. The person even confesses. I have a big bump on my head but no recollection of what exactly happened.

    I would suggest that the evidence for this event having happened (the robbery) is actually more than what I personally experienced.

  3. I don't think the bible is a science book detailing how everything was created by the Almighty. As a science book it does a terrible job. The creation story tells of increasingly complex living organisms, from bacteria to mankind. It is possible that at some point along the evolutionary chart that the Almighty breathed a "soul" a neshema, not a nefesh, into the human man we know today.

  4. "It is possible that at some point along the evolutionary chart that the Almighty breathed a 'soul' a neshema, not a nefesh, into the human man we know today."

    Please elaborate, as I disagree that this is possible. It sounds like make-believe.

  5. Anonymous3:20 PM

    Yes, but inevolution you only get the wallet not the confession.

  6. Yes, but inevolution you only get the wallet not the confession."

    Uh, OK. But my point had to do with quantity/quality of evidence relative to personal experience.

    Besides, with theism we get neither the confession nor the wallet.

  7. This comment has been removed by the author.

  8. The real issues with evolution you have completed avoided:
    a) Cambrian layer fossils - near all phyla appearing in a 5-10 million year period with no transitions or ancestors (even Darwin proposed this as a huge issue to his theory and yet no fossil evidence has still been found 100 years later)
    b) That there is no unambiguous example of one species changing to another based on accumulated mutations
    c) How did life start from non-living matter in the first place? In order for evolution to work, there has to be living matter
    d) Downward causation - most changes to species actually cause a loss of genetic information, not addition - this has been shown via bacteria that are resistant to certain drugs


Feel free to comment if you have something substantial and substantiated to say.