My Life with Darwin

A Report on Evolution from the Laboratory Bench

When other Christians hear that I’m a biomedical scientist, they sometimes ask how I deal with evolution. This question could mean several things: First, do the evidential claims of “evolution” compel assent from someone who has studied biology as much as I have? Second, am I under any pressure from my colleagues and superiors to submit to its tenets? Third, does the “theory of evolution” constitute such a compelling and all-encompassing paradigm that I can’t address scientific questions without reference to it?

Now “evolution” may mean any of several things to the person asking the question. Sometimes it means natural selection acting upon random genetic variations to produce distinct traits in a population of a particular species, or what is sometimes called microevolution. When I hear the word “evolution,” the idea that comes to my mind, and I suspect also to that of many others, is that “all present species have arisen from a single common ancestor by descent with genetic modification.” This, however, is not the fullest, strictest, most “official” sense of the term. Darwin, whose theory became the basis for the modern paradigm, proposed that the mechanism by which present species came about was natural selection acting upon random, heritable variations (genetic variations, we would say now). It is with this classical “Darwinism” that I am concerned here.

So, if by “evolution” one means “Darwinism,” then my answer to the first question above is “No.” I am not convinced that natural selection as Darwin and his followers conceived it is sufficient to explain all the features of the biological world. I am skeptical of the sufficiency of one-chance-mutation-at-a-time steps to account for the variety and complexity of living creatures.

My answer to the second question is also “No,” mostly, I assume, because of the more technical and less theoretical nature of my training and research. I have never experienced a direct conflict with the reigning Darwinist paradigm. Nor have I ever been asked explicitly to assent to the common descent of all species, or to affirm natural selection as the creative force behind the diversity of life. The issue simply never comes up in that way. The assumption that Darwinian evolution is true, however, does permeate academic culture.

Multiple Meanings

In my field, that assumption presents itself in several ways, which brings me to the third question: Is it possible to live and think as a scientist and make scientific progress without dependence on Darwin’s theory? To answer this question, I will consider three ways in which the word “evolution” is used in the presentation of research, the meaning behind each use, and the relation of each use to Darwinism.

As an immunologist, my observations pertain to immunological research, which overlaps microbiology, cellular biology, molecular biology, physiology, pathology, and many other disciplines, so my observations pertain in part to them, too. They do not apply to genetics, evolutionary biology, or like disciplines that concern themselves specifically with origins and descent.

In the world of biomedical research, the term “evolution” is used frequently, but no distinction is made between its various meanings. For example, a debater or theorist may carefully distinguish “microevolution” from “macroevolution” or “Darwinism” from “theistic evolution.” But in the everyday usage of the biologist, “evolution” is not simply how mosquitoes acquire insecticide resistance and viruses become unrecognizable to the immune system; it is also the bestower of light upon fireflies; and it is the process by which mice and men and fruit flies all arose from a common ancestor—in other words, it is “all of the above.”

Evolution Means History

When the word “evolution” appears in an immunological paper or lecture, it assumes that all present life forms arose by descent from a single (or a few) common ancestor(s), with the accumulation of genetic modifications bringing about the present complexity and variety of forms. This use of the word is seen in statements such as, “Gene/protein X is evolutionarily ancient,” “ Y and Z are believed to have arisen by gene duplication,” or “ W diverged relatively recently from V.”

Thus, an analysis of a particular gene in a particular organism is considered to yield information about the history of the biological world. The degree of genetic difference between two organisms is an indicator of the number of generations, and therefore of the length of time, that must have passed since they had a common ancestor.

Commonalities in genetic information are supposed to predate that common ancestor. These are graphically illustrated by phylogenetic trees—diagrams that depict the paths and distances of descent in a given group of organisms. Each member of the group in question is connected to the others by branching lines whose length is proportional to the time that has passed—or the number of mutations that have occurred—since they had a common ancestor (Fig. 1). Branch points (“nodes”) in the diagram symbolize a common ancestor of the organisms connected to it. The degree of difference between each member of the group is compared, and used to estimate the time since divergence.

Sometimes, the differences that are counted are differences in anatomy or physiology. A more mathematically precise estimate is obtained by counting the number of differences (“substitutions”) in the sequence of nucleotides (chemical building blocks) in DNA, or in the sequence of amino acids in protein. Essentially, a phylogenetic tree is a genealogical chart deduced from genetic analysis and an assumption of common descent.

In biomedical literature, phylogenetic trees may compare groups of organisms as closely related as several strains of the same bacterium or as dissimilar as the roundworm C. elegans and H. sapiens. No distinction is made between “microevolution” and “macroevolution”; it is all the same process. But in immunological literature at least, a phylogenetic analysis is more often focused on one gene or close group of genes the author of the study happens to be interested in, than on an entire organism.

Does the use of phylogenetic trees and similar historical deductions indicate agreement with Darwin? They do imply agreement that (1) the organisms included in the diagram are descended from a common ancestor, and (2) genetic changes accumulate over time through the lineage. So they do imply “evolution” in some sense of genetically distinct organisms from another distinct ancestor.

Therefore, if a diagram includes widely different species, it does imply a kind of evolution that at least is as biologically all-encompassing as Darwinism. However, the key point of Darwinism is that natural selection of inherited variations is the mechanism by which all biological diversity is generated (Gould, The Structure of Evolutionary Theory, 2002). A phylogenetic tree, simply tracing the number of differences between organisms, gives no information about what reproductive advantage any one of those differences may give to its possessors. It can say nothing about whether, or why, any of those differences is or has been selected for or against. Its use, therefore, does not necessitate an embrace of Darwinism per se.

Evolution Means Conservation

A second and closely related assumption of the evolutionary paradigm is expressed in the phrase “evolutionarily conserved” when it refers to a nucleotide sequence (of a gene, for instance), an amino acid sequence (of a protein), or even a whole protein that is the same in many disparate species. The idea of evolutionary conservation is frequently used in deciding which parts of a sequence (nucleotide or amino acid) are most important to a protein’s (or cell’s) function.

The reasoning goes like this: If many distantly related species all have (for example) amino acid A at position 203 in Protein Z, then probably any mutations that put a different amino acid there rendered Protein Z non-functional and the organism unfit, and thus doomed to elimination by natural selection. In fact, experimental analyses of conserved sequences often reveal important functions of those parts of the gene or protein.

The concept of evolutionary conservation is a strength of Darwinism. A scientist who is skeptical of Darwinism might retain the idea of “conservation” while dropping the “evolutionary” part of it; after all, a sequence that was carried in almost the same form by species that differed in almost everything else might reasonably be thought to be important, no matter what one’s theory of origins. The scientist would have to concede, however, that Darwinism provides a neat mechanistic explanation of the phenomenon, a cause-and-effect of why it must be so.

Evolution Means Purpose

Thirdly, the term “evolution” is invoked in the same way that God, or more recently, Nature, used to be, as the Source of meaning and End of being. Even though most biologists are strict practical materialists as they pursue their inquiries, there is a deep, persistent conviction that the new facets of biology they are discovering must have a reason behind them—and if it’s not obvious, they will try to think of one. But it is from and for Evolution that the reason is sought.

So, for example, where a theist would ask, “Why did God make it thus?”, the evolutionist asks, “Why did Evolution make it thus?” Hence, a reviewer of one of my papers asked me to explain why evolution would have preserved the existence of the phenomenon I was reporting. The discussion sections of many treatises contain speculation as to the “evolutionary advantage” of whatever it is the authors have observed.

“What is the evolutionary advantage of X?” is also one way of simply asking, “What good does this thing you observe do for the organism that possesses it?” The question can be satisfactorily answered by pointing out how whatever-it-is helps the creature survive and reproduce.

Why, though, should we expect any part or property of an organism to be useful to that organism? A theist in the Judeo-Christian tradition would look for advantageous functions as a provision of a good and rational God. For the atheist, Evolution provides an alternative basis for assuming that what we observe has a function—that it has a purpose intelligible to us. It is in this respect that it appears as an alternative metaphysical system opposed to theism.

Evolution Avoidable

Darwinian evolution is the touchstone of thought concerning history and purpose in the world of biomedical research. Skeptics are thus open to the accusation of being unscientific, of basing their thought—even if presented in scientific form by credentialed scientists—elsewhere, particularly in religion, because its underlying theorems are untestable by scientific means. This, however, leaves the atheist open to the counter-charge of substituting a faceless, but equally puissant and ineffable Intelligence—“Evolution”—for God.

In wide swaths of the scientific world, including the one in which I work, history and purpose are not primary concerns. Rather, the bulk of time and ink is spent describing phenomena and mechanisms that do not depend on any particular theory of origins. Because of this, it is not necessary to invoke Evolution in the course of research and publication.

Martha Hutchens received her Ph.D. in immunology from the University of Michigan, where she studied the immune response to vaccinia virus. As an undergraduate, she did research at Michigan State University developing a test for infection by the oomycete pathogen Pythium insidiosum. She is currently a postdoctoral fellow at Vanderbilt University Medical Center, where she studies intracellular signaling pathways controlling inflammation.