by Joanna Masel

You might expect a professional evolutionary biologist like myself to claim that my discipline has nothing to learn from creationists. And I certainly do find all flavors of evolution-denialism sadly misguided. But I also find it reasonable to assume that any serious and dedicated critic should uncover something interesting about the object of their obsession. I’m not talking about passing trolls here. I’m talking about earnest and sometimes talented people whose sincerely held anti-evolution convictions do not preclude engagement, and who invest a lot of time thinking about evolution from an unconventional perspective.

I draw three main lessons from such critics. First, there is plenty to learn about human psychology from the rejection of evolution. Why do so many people not accept scientific conclusions that seem to an expert like me to be irrefutably supported by the evidence? Dismissing the cause of their rejection as religious ideology only shifts the question. Why do so many ideologies take that particular form?

Listening to those who deny or are at least uncomfortable with evolution, it quickly becomes clear that most are relatively unconcerned about the evolution of microbes. Instead their objections dwell on the evolution of humans and our relationship to other animals. This notion that humans are special, not only in a theological sense, but also in concrete ways that should be amenable to scientific study, is often at the core of people’s discomfort [1]. In other words, objections tend to focus less on the implications of evolution for God than on the implications of evolution for the significance (or rather, the insignificance) of human lives. An uncomfortable message from science, including cosmology as well as evolution, is that we humans are much less significant — in the broad scheme of things — than we like to think. This discomfort is not restricted to creationists.

In this view, evolution-denialism is a case study for a far more widespread phenomenon known as human exceptionalism, which in non-creationists takes more subtle forms that are harder to detect. Indeed, science itself can and has been distorted by the notion of human exceptionalism; the related notion of “progress” in evolution has been particularly pernicious in this sense [2].

It is hard to stay objective about human affairs. The same principles of evolutionary biology apply just as well to humans as they do to other species. But on average, those principles will be applied less objectively to humans than to other study organisms. Because scientists are human too.

The big two topics studied by evolutionary biology are sex and death [3]. We make these topics sound more dry and technical by calling them survival and reproduction. Whatever words we use, these are not easy topics to remain objective about, especially when it comes to humans.

The lesson I take for myself, as a professional evolutionary biologist, is the need to hone my thinking and my tools on unproblematic species such as microbes. The scientific study of mating types a and alpha in the yeast Saccharomyces cerevisiae is relatively unsullied by attitudes towards sexism or feminism. I find it easier to maintain objectivity when discussing yeast reproductive strategies than when discussing human reproductive strategies.

Once my epistemic skills are honed by the application of evolutionary biology to yeast, and hence relatively unsullied by the taint of human exceptionalism, I am in a good position to make occasional forays into the study of human questions. The key to gaining evolutionary insight into human affairs is to make sure that my methods of reasoning and standards of evidence remain the same for the study of humans as they are for the study of yeast. But I try not to think about humans for too long, lest my own biases about our species erode my scientific standards. This is an important cautionary lesson that I have learned, in part, from creationism.

Leaving aside human exceptionalism, where do other objections to evolution come from? I am especially interested in more thoughtful objections from the scientifically trained. Interestingly, some of them come from biochemistry; in particular, the idea that some biological systems are “irreducibly complex” at the molecular level [4].

The source of this objection in biochemistry is revealing. As an evolutionary biologist, I am shocked at the poor grasp of evolutionary concepts among many (non-creationist) biochemists and molecular biologists, and I am not alone in this view [5]. Students in these fields are taught how cells work using diagrams and 3D animations where each molecule somehow knows what it is supposed to do, and efficiently does only that. The colossal mess, waste, redundancy, and confusion of real molecular processes, although increasingly apparent in today’s era of systems biology, are generally ignored in biochemistry and molecular biology classrooms. Students are presented with images of clean molecular machines [6], backed up by canonical and unrepresentative examples, e.g. from viruses. No wonder some of them then find intelligent design intuitive! If students knew just what an inefficient mess real biological systems fundamentally are, they might be more open to the frequently unintelligent nature of “design” via natural selection.

Biochemistry was in its infancy at the time when biology went through the purging process known as the modern evolutionary synthesis, in which the field of biochemistry did not participate [2]. The disciplines of biochemistry and molecular biology were offshoots of chemistry, not biology. A synthesis of biochemistry with evolutionary thought is much-needed and overdue [7]. The second lesson I draw from creationism is the urgency of this task.

Going back to the specific irreducible complexity objection to evolution, the biochemist Behe writes [4]:

“By irreducibly complex I mean a single system composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning. An irreducibly complex system cannot be produced directly (that is, by continuously improving the initial function, which continues to work by the same mechanism) by slight, successive modifications of a precursor system, because any precursor to an irreducibly complex system that is missing a part is by definition nonfunctional. An irreducibly complex biological system, if there is such a thing, would be a powerful challenge to Darwinian evolution.” (p. 39)

The most common response from evolutionary biologists is to say that irreducible complexity is only an illusion. Systems that perform one function can be co-opted for a different function, making it difficult to trace the exact series of successive one-step modifications by which it evolved. And there is a lot of truth in this response.

But nonetheless, I think Behe asked a good question. Can irreducibly complex adaptations evolve? Behe is not the first person to ask this question, by a margin of about six decades [8]. In the technical jargon of evolutionary biology, we call this “crossing a valley on the genotype-fitness landscape.” It is believed to be difficult, but possible under some circumstances [9,10].

My colleagues and I just published a paper identifying circumstances in which the crossing of wide adaptive valleys, i.e. irreducible complexity, is not just possible, but common [11]. And we made the decision to put “irreducible complexity,” a term coined by a creationist, in the title of our paper. Why? Because it’s a good term. It’s a much better term than using a continuous metaphor of a “landscape” to describe a discrete space, among other known flaws of the term [12, 13]. And the definition in Behe’s book is a good definition. I am happy to give credit where credit is due, including to a creationist.

The topic of irreducible complexity / valley-crossing was understudied in evolution until recently, and deserved more attention than it was getting. Where Behe sees the concept of irreducible complexity as an illustration of the failure of the theory of natural selection, I see it as pointing to a set of exciting and understudied evolutionary biology problems.

Think for a moment about an intelligent and otherwise rational person who hates a scientific theory for religious or other ideological reasons, desperately wants to prove that idea wrong, and is willing to work hard to undermine it. That person is going to identify the weakest points in the theory. For the theory of evolution by natural selection, those weak points are overwhelmingly unlikely to be weak enough to undermine the theory as a whole. But they are likely to point to really interesting and understudied questions that I might want to do research on next! I see a weak spot in evolutionary theory not as a problem, but as an opportunity for me to work on the topic and make it stronger, possibly making exciting scientific breakthroughs along the way.

This is the third lesson I draw from creationists. Some evolutionary biologists are afraid to even discuss topics highlighted by creationists, fearing that this could be seen as an unnecessary concession of weakness of the powerfully supported theory of evolution by natural selection. I disagree with this reasoning.

Behe believes that irreducible complexity occurs, that this would be impossible via evolution by natural selection, and hence that evolution by natural selection must be wrong. In contrast, I am intrigued by the fact that irreducible complexity might occur, believe that if it does occur then of course it occurs via evolution by natural selection, and conclude that my job as an evolutionary biologist is to work out how.

The answer in our paper, in part, was that evolutionary biologists had been asking the question wrongly. They were defining both a starting point and an end point for evolution across a valley in genotype-fitness space. But evolution does not move towards one particular end. The possibilities are, if not limitless, then combinatorially large. Say you have 100 mutations to choose between in the search for a fitter genotype. That means you have up to 100-choose-2 = 4,950 2-way combinations available to you. And you have 161,700 3-way combinations and nearly 4 million 4-way combinations. Even if finding any particular irreducibly complex adaptation is extraordinarily unlikely to evolve, this must be balanced against the extraordinarily huge number of potential complex adaptations. And for this reason, we were able to find circumstances under which irreducible complexity was not only possible, but actually common [11].

In other words, space is big. Not just the big physical space that we are familiar with from astronomy, but also the more abstract genotype space of all the things that are possible. We humans have limited intuitions about spaces that big, but we can overcome our cognitive limitations through the use of formal mathematical models. And in some of those models, irreducible complexity is a common phenomenon.

Continuing with this third lesson, my future plans for the study of evolution include Behe’s observation of the predominance of loss of function mutations in observable evolution [14] and a question that sometimes goes by the name of “Haldane’s dilemma” [15]. I think some really exciting evolutionary biology lies ahead.

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Joanna Masel is an evolutionary biologist at the University of Arizona. Her research investigates the robustness and evolvability of biological systems and the nature of different types of competition in both biology and economics.

[1] Mix LJ, Masel J (2014) Chance, Purpose, and Progress in Evolution and Christianity. Evolution 68: 2441-2451.

[2] Provine WB (1989) Progress in evolution and meaning in life. In: Nitecki M, editor. Evolutionary Progress. Chicago: University of Chicago Press. pp. 49-74.

[3] Sterelny K, Griffiths PE (1999) Sex and Death: An Introduction to Philosophy of Biology. Chicago: University of Chicago Press.

[4] Behe MJ (1994) Darwin’s Black Box: The Biochemical Challenge to Evolution. New Jersey: Free Press.

[5] Graur D, Zheng Y, Price N, Azevedo RBR, Zufall RA, et al. (2013) On the immortality of television sets: “function” in the human genome according to the evolution-free gospel of ENCODE. Genome Biology and Evolution 5: 578-590.

[6] Boudry M, Pigliucci M (2013) The mismeasure of machine: Synthetic biology and the trouble with engineering metaphors. Studies in History and Philosophy of Biological and Biomedical Sciences (4):660-668.

[7] Harms MJ, Thornton JW (2013) Evolutionary biochemistry: revealing the historical and physical causes of protein properties. Nat Rev Genet 14: 559-571.

[8] Wright S (1932) The roles of mutation, inbreeding, crossbreeding, and selection in evolution. Proc 6th Int Cong Genet 1: 356-366.

[9] Weissman DB, Desai MM, Fisher DS, Feldman MW (2009) The rate at which asexual populations cross fitness valleys. Theoretical population biology 75: 286-300.

[10] Weissman DB, Feldman MW, Fisher DS (2010) The Rate of Fitness-Valley Crossing in Sexual Populations. Genetics 186: 1389-1410.

[11] Trotter MV, Weissman DB, Peterson GI, Peck KM, Masel J (2014) Cryptic Genetic Variation Can Make “Irreducible Complexity” a Common Mode of Adaptation in Sexual Populations. Evolution in press.

[12] Provine WB (1986) Sewall Wright and Evolutionary Biology: University of Chicago Press.

[13] Pigliucci M (2012) Landscapes, surfaces, and morphospaces: what are they good for? In E. Svensson & R. Calsbeek (eds.), The Adaptive Landscape in Evolutionary Biology. Oxford: Oxford University Press, pp. 26-38.

[14] Behe MJ (2010) Experimental evolution, loss-of-function mutations, and “the first rule of adaptive evolution”. The Quarterly review of biology 85: 419-445.

[15] Remine WJ (2006) The Biotic Message: Haldane’s dilemma.