Is there such a thing as macroevolution?

Even creationists make progress. While young-earth creationists are stuck where science was back in the seventeenth century (most of them do accept the findings of Copernicus and Galileo), an increasing number of them agree that natural selection happens and that it can account for some of the variation found among living organisms in nature (thereby jumping all the way to the middle of the nineteenth century!). However, they hasten to add, this is "just" microevolution, and the real beef is with macroevolution. That, they argue, cannot possibly be explained by Darwinian processes.

I'm afraid that scientists are largely responsible for this misunderstanding and moreover are not doing much to correct it. The words micro- and macroevolution do appear in the scientific literature--which, of course, is where creationists got them to begin with. The problem is that evolutionary biologists ever since Darwin (who didn't use those words) have disagreed about where the distinction lies, or whether there even is a distinction at all!

Most professional biologists today think of microevolution as evolution within species and of macroevolution as what happens over time to differentiate species or "higher" groups of organisms (genera, families, etc.). Darwin would disagree, as he thought that species were just arbitrary boundaries imposed by humans on what is otherwise a seamless continuum of variation. According to Darwin, evolution happens all the time in the same fashion (a theory called uniformitarianism, which was first applied by Charles Lyell--who greatly influenced Darwin--to geological processes). Thomas Huxley, "Darwin's bulldog," as he was known for his tenacious defense of evolutionary ideas, disagreed, and admonished Darwin that the hypothesis of gradual and uniform change was simply unnecessary to the theory.

The controversy has raged since, and there is no end in sight. During the 1930s and 1940s, biologists achieved what is now known as the "Modern Synthesis" of evolutionary theory. The synthesis is a unification of classical Darwinism with the (then) new science of genetics, and it is a triumph of twentieth-century science. Yet, even during its early days, it encountered fierce (scientific) critics. Most famously, German geneticist Richard Goldschmidt contended that mutation and natural selection--the fundamental mechanisms of the Darwinian synthesis--do a good job at explaining variation within species but are insufficient when it comes to understanding so-called "evolutionary novelties." Novelties are structures or behaviors that arise from time to time and that often play a major role in the ecological success of the species that carry them. For example, birds evolved from dinosaurs and display the evolutionary novelty of powered flight, a hugely successful trait in terms of the sheer number of species that have it.

Goldschmidt thought that biologists had not yet uncovered the explanatory principles that make evolutionary novelties possible, and creationists have seized on the idea and turned it into annoying mindless mantra like "What good is half an eye?" (The answer, it turns out, is about half as good as a full eye, as we now have a reasonably detailed idea of how eyes repeatedly evolved from simple light receptors.) Goldschmidt's own answer, that genome-wide rearrangements occasionally take place and result in radically different life forms, which he nicknamed "hopeful monsters," was reasonable at the time, but has been shown to be incorrect on empirical grounds (that's the way real science proceeds, of course, as opposed to grand declarations from the pulpit).

Yet, the problem is still with us. I recently returned from a three-day conference at Indiana University on the problem of evolutionary novelties. No creationist there, but little agreement among the scientists present on what the best explanations are for the appearance of novelties. Some of my more conservative colleagues--like Darwin before them--saw no problem at all, arguing that the conceptual tools of the Modern Synthesis are sufficient for the task and we only need to work out the details. Others, including myself, disagreed and proposed a variety of other venues of inquiry (including somewhat obscure phenomena like phenotypic plasticity, epigenetic inheritance, and emergent complexity).

The important point to understand here is that there is indeed a legitimate scientific debate, but that it has nothing to do with the sort of "debate" that creationists have in mind. None of the participants in the Indiana conference doubts that the Modern Synthesis is the correct account of a large part of biological phenomena. Also, nobody there denied that the answer to the question of evolutionary novelties requires only natural phenomena and is perfectly compatible with all the laws of physics. This isn't a statement of faith, just a common-sense approach that all scientists take and that is known as methodological naturalism, the idea that even if the supernatural exists, it cannot play any role in scientific explanations (because science is, by definition, well, about nature).