Modern Evolutionary Theory (neo-Darwinism)

We have thus far talked about a lot of terminology, and we are in a position now to pull more pieces of the puzzle together into a coherent picture of what so-called “neo-Darwinism” or the “neo-Darwinian synthesis” really is.

“Darwinism” vs. the “neo-Darwinian synthesis”

Whenever a critic attacks “Darwinism,” scientists almost always respond by complaining that “The neo-Darwinian synthesis is nothing like the ‘Darwinism’ of old, as we know so much more today about how evolution works. So, attacking ‘Darwinism’ is not really an attack on contemporary evolutionary science.”

This sort of response is always coupled with claims along the lines that, “Evolutionary theory is a theory; it is also a fact” (Dawkins and Gould), and, “Evolutionary theory is arguably the most verified scientific theory in existence.” And these claims rest entirely on the “synthesis” of Darwinian natural selection with Mendelian genetic theory. Because Mendelian genetic theory has been fruitful indeed, it is easy for evolutionists to point to the “verifications” of Mendelian theory as “verifications” of the “neo-Darwinian synthesis.” Thus, if a critic attacks “Darwinism,” it is presumed by scientists that the critic is ignorant of the sweeping “verifications” of “evolutionary theory,” when in fact the critic might well accept Mendelian genetic theory whiile denying its explanatory value in evolutionary theorizing, and the critic might also flatly deny the usefulness of natural selection in the evolutionary account. So, the virtually slight of hand move on the part of evolutionists to “disarm” supposedly ignorant critics really amounts to a word-game and conflation of two unrelated concepts!

Nevertheless, we must be careful with our terms. So, again and again I explicitly state that when I talk about “evolution,” “evolutionary theory,” or “Darwinism,” I take these to all be shorthand terms for “the neo-Darwinian synthesis,” because I explicitly acknowledge the contemporary coupling of natural selection with Mendelian genetic theory in contemporary evolutionary theorizing. When I say “Darwinism,” it is just shorthand, because “the neo-Darwinian synthesis” is a mouthful!

So, there are two components we must now contemplate: Natural selection and Mendelian genetic theory. We will be devoting an entire week to the concepts packed into natural selection, so we won’t address those here. Besides, Mendelian genetics is the “neo” aspect of contemporary Darwinism. Thus, it is the most pressing consideration for us this week, and we need to get clear enough about genetics that we can talk intelligently about  what the natural selection process is “selecting” upon in the first place.

Mendelian Genetics

Darwin rejected Lamarckism, with its notion of “inherited characters” and vitalism. Most people of Darwin’s era that rejected Lamarckism believed instead in some form of “blending” of characteristics, whereby parental characteristics could be seen in their offspring. Darwin also believed in a “blending” notion of passed-down characteristics.

Mendel, at about the time of Darwin’s Origin of the Species, was performing the famous pea plant experiments that would explain in mathematical detail how parental characteristics were passed down in offspring. And, coupled with the work of Thomas Hunt Morgan (chromosome theory), the term “Mendelian genetics” eventually became synonymous with “Classical genetics.” Mendel’s laws, though largely rejected in his time, have come to be recognized as broadly applicable and correct. What Mendel lacked was the vehicle of the transmission of “genes,” what we now understand to be chromosomes. However, his “laws of genetics” provided a mathematically robust predictive model of the genetic heredity that is carried and passed along via chromosomes.

The progression of understanding from Darwin through Mendel to “classical genetics” to the “neo-Darwinian synthesis” is well summarized in the abstract of an article by Brian and Deborah Charlesworth, “Darwin and Genetics,” published in the journal Genetics and available at the National Library of Medicine, National Institutes of Health website. The Charlesworths write:

Darwin’s theory of natural selection lacked an adequate account of inheritance, making it logically incomplete. We review the interaction between evolution and genetics, showing how, unlike Mendel, Darwin’s lack of a model of the mechanism of inheritance left him unable to interpret his own data that showed Mendelian ratios, even though he shared with Mendel a more mathematical and probabilistic outlook than most biologists of his time. Darwin’s own “pangenesis” model provided a mechanism for generating ample variability on which selection could act. It involved, however, the inheritance of characters acquired during an organism’s life, which Darwin himself knew could not explain some evolutionary situations. Once the particulate basis of genetics was understood, it was seen to allow variation to be passed intact to new generations, and evolution could then be understood as a process of changes in the frequencies of stable variants. Evolutionary genetics subsequently developed as a central part of biology. Darwinian principles now play a greater role in biology than ever before, which we illustrate with some examples of studies of natural selection that use DNA sequence data and with some recent advances in answering questions first asked by Darwin.

In the above passage, there are a number of concepts worth special attention.

We see explicitly stated that “Darwinism” was an “incomplete” theory. This is precisely why contemporary evolutionists get up in arms when critics refer to “Darwinism.” As the Charlesworths state, it is the coupling of “Darwinian principles” with the “particulate basis of genetics” that makes up “classical genetics” that collectively form the “neo-Darwinian synthesis” that is oh so superior than mere “Darwinism.” Now, we are told, “Evolutionary genetics… [is] a central part of biology,” and “Darwinian principles now play a greater role in biology than ever before.” Put Darwin together with Mendel and Morgan, and what you get is the very basis of contemporary thought in biological science. Indeed, many biologists have echoed the sentiment that, “You just can’t do modern biology apart from evolutionary theory.”

Micro vs. Macro Evolution

The problem with articles like “Darwin and Genetics” is repeated throughout the literature. And that problem can be cast as the gulf between “adaptation” and “speciation events.” Contemporary “evolutionary biology” has proved to have tremendous value and predictive power insofar as it deals with genetics on a micro scale and addresses true adaptation. However, it remains pure speculation that, “If you put enough micro events together over a long enough period, you will eventually get a speciation event, and ultimately you will get enough genetic drift that the results are not even close to the original.”

The evidences of micro evolution and adaptation are endless! Indeed, this is the part of statements like, “Evolution is theory, but it is also a fact,” that is true. Micro evolution is indeed “verified” by countless observations and experiments! And classical genetics, coupled with some sort of “natural selection,” does indeed offer a robust theoretical model to explain how adaptation works. So, the “neo-Darwinian synthesis” appears to have tremendous explanatory power and be continuously “verified” by observation and experiment. And this is why evolutionists howl at and mock creationists that appeal to the “problems with Darwinism,” as though Darwin was the pinnacle of evolutionary theorizing.

We will soon get into so-called “speciation events” in great detail, so we won’t duplicate that work here. But most biologists today find the inferential leap from micro to macro evolution so intuitive that they never think to question it. Put enough small changes (adaptations) together over time, and of course you are going to get enough genetic drift that a “starting species” will ultimately not even resemble a “resulting species.” It’s the tiny, stepwise, “no big leaps” process that is the earmark of “evolutionary theory” exactly as Darwin imagined it!

So, classical genetics is rock solid. Some sense of natural selection (adaptation) is rock solid. Evolutionists have a genetic transmission model that is wholly naturalistic, coupled with the “fitness filter” that parses among passed-down characteristics to determine which of them get to be yet further passed down, and the two processes together are a complete account of the mutability of the species. Thus, the neo-Darwinian synthesis has achieved the status of a true paradigm, and “normal science” is in full force within that paradigm.

But what does it mean? What really is “evolution” as scientists today think of it? Even talking about “adaptation” or “micro evolution” is not really fine-grained or accurate enough!

Ernst Mayr wrote in 1982 that “evolution” is best defined as: “changes in trait or gene frequency in a population of organisms from one generation to the next.” This definition has met with widespread acceptance. Notice that nothing is said about the specific mechanism of change; the mechanisms can include natural selection or other mechanisms thought to cause gene mutation and adaptation. But at core, “evolutionary theory” is the set of laws and principles that collectively presume to explain how trait and gene frequency within a population change over time.

Notice that even this fine-grained notion of “evolution” presumes that enough micro changes over time will produce macro changes. Again and again, regardless of how famous scientists cast the issue, we come back to the idea that “evolutionary theory” explains small-scale genetic changes within a population (micro evolution) that can legitimately be projected through time into large-scale changes (macro evolution). So, let’s first examine the nature of these small-scale changes.

The best and most accessible article I have found is this one: Theobald, Douglas L. “29+ Evidences for Macroevolution: The Scientific Case for Common Descent.” The Talk.Origins Archive. Vers. 2.89. 2012. Web. 12 Mar. 2012 <http://www.talkorigins.org/faqs/comdesc/>

Rather than to reinvent the wheel, it is far better to let an evolutionary scientist explain the case for himself, which is what Theobald does in the foregoing article.

Notice that many of Theobald’s points do not relate to what could strictly speaking be called “adaptation.” Adaptation is just one presumed sort of micro evolution, one in which environmental pressures produce successive generations of a species evidencing “changes in trait or gene frequency,” where the trait or gene in question existed throughout the population, but the frequency of a selected trait changes, typically increasing.

The all time classic example is the peppered moth. Prior to the industrial revolution, the uniformly dark-colored variant made up about 2% of the population (the frequency of the trait, which, of course, is a reflection of the frequency of the dark-coloration gene). After the industrial revolution, with the soot deposits from factories darkening the tree trunks on which the peppered moth lives, the dark-colored variant made up about 95% of the population.

By the strict, genetic definition of “evolution” cited above, this is a clear-cut case of “evolution.” Trait and gene frequency most certainly did change within the population over time. This is an example of both micro evolution and adaptation. It is specifically adaptation because the change in trait frequency came about as a direct result of environmental pressure, particularly predation upon light-colored moths residing on dark, soot-covered tree trunks. Birds almost killed off the light-colored moths, presumably because the birds could see the moths better. The dark-colored moths largely escaped this predation, resulting in the vast majority of the peppered moths having the trait for uniformly dark coloration. By contrast with “adaptation,” trait and gene frequency can change in the absence of environmental pressure (mutations, for example, that have not yet resulted in “selectable” morphological changes). So, the peppered moth is a classic example of micro evolution and adaptation.

There are other such examples. We will consider just a few here.

Blue mussels in New England adapt to predation from the invasive Asian shore crab; where the shore crab is plentiful, the mussels have significantly thicker shells.

Darwin’s Finches in the Galapagos Islands are another classic and oft-referenced case of micro evolution; the finches on different islands have developed different bill shapes and strengths in response to the various seeds and nuts available to them for food.

Drug resistance in bacteria is another classic example of both micro evolution and adaptation. Both in the human body and in laboratory cultures, a given drug will kill off 99+% of a population of bacteria, but a tiny percentage will possess immunity to that drug. That tiny percentage of the population will then multiply and become virtually the totality of the population. Thus “trait and gene frequency changes within the population” regarding resistance to the particular drug.

What is notable about all cases of adaptation is that they satisfy the strict definition of “evolution,” showing “natural selection” in action on a population, but in every case there is no “new” genetic information that is being “selected” within the species.

For example, in the case of the peppered moth, the population always had a distribution of light and dark-colored moths. The genetic information for both variants existed in the species. The frequency of the dark colored trait increased, but never to totality. In fact, the light-colored trait maintained a higher than 2% distribution (5%) even in the face of decimating predation, while prior to the industrial revolution the incidence of the dark-colored trait was about 2%. So, it could even be argued that “nature prefers” the light-colored variant even in the face of intense predation. The point is that neither the dark-colored nor light-colored variant ceased to exist, indicating that the underlying genetics for coloration varies without affecting anything else about the moth as a species; the moth is not “becoming” a new species. The species simply has coloration as a “derived” trait (in cladistic terms), and there is “nothing new” about peppered moths during this “process of evolution” that resulted in a widespread color change. And both light and dark-colored moths breed and reproduce, producing offspring with some distribution of the genetic disposition to be light or dark-colored.

The same points can be made in the other cases, such as the blue mussel. The population is not “becoming” anything other than blue mussels, and the “derived” trait is an isolated trait in the species response to environmental pressure.

The best examples of micro evolution, indeed the “textbook” classics, represent only and exactly micro evolution, specifically adaptation. But nobody denies that micro evolution is real, and nobody denies that adaptation to environmental pressures will produce a different distribution of the traits relevant to that environmental pressure. Cases like the peppered moth demonstrate nothing of importance in the conflict between evolutionists and creationists.

What evolutionists need to demonstrate is at least:

  • Actual observation of macro evolution resulting from micro evolution.
  • Macro evolution resulting in both morphological and genetic variation among “related” populations, such that the populations have “come apart” sufficiently that interbreeding is no longer possible, which is the best definition of a “speciation event.”

Thus far, demonstrated examples of micro evolution have been strictly genetic changes lacking in morphological traits, rendering these changes transparent to natural selection; or the micro evolutionary examples have demonstrated only adaptation, which does not correlate with actual genetic “change” in the population. So, the examples of “new” information don’t demonstrate selective responses, and examples of selective responses don’t demonstrate “new” genetic information. (The case of the Blue Moon butterfly is particularly interesting in the context of this paragraph, and we will look at it in upcoming weeks.)

The point is that “change in the frequency of a trait or gene” in a population is a very, very low bar for evolutionists to get over! Such changes need not introduce “new” genetic information into the species. And any “new” genetic information (resulting from, say, mutation) need not present any morphological evidence. What is at issue in macro evolution is how mutable the genome of living things actually is, which is to question how much genetic change can accumulate in the genome of any particular species.

That issue can only be addressed by both sides of the conflict admitting that micro evolution is a fact, but that the theory that suggests that micro evolutionary changes can accumulate indefinitely and produce vast morphological changes (including wildly disparate species) is really the contentious aspect of “evolution.” And that contentious notion of “evolution” cannot be resolved by simply pointing to more and more examples of micro evolution. Both sides need to see demonstrations of actual speciation events resulting from micro evolution over time and preferably resulting from natural selection (since we are, after all, talking about Darwin’s theory here).

Mere inferences from the fossil record will always be contentious. If these are not coupled with “evolution in action,” namely speciation events resulting from natural selection, then the most impressive, and really contentious, claims of evolutionary theory remain unsubstantiated.

So, next week we will turn our attention to natural selection. The following week we will examine purported speciation events.