Micro vs. macroApril 14, 2009 — Deacon Duncan
As usual, I’m way behind in my comment reading (I’m up to Feb. 27th in my backlog), but I’m seeing references to micro vs. macro evolution in the comments, and since I’ve come across this sort of discussion before, I thought I might step in and clarify my point a little.
The behavior of rivers is, broadly speaking, fairly easy to explain: water flows downhill. If your specialty is the study of rivers, however, you might want to dispute the claim that all rivers work in essentially the same way. You might want to point out different mechanisms of erosion and silt deposition, and how that interacts with the river to produce variations in the rate of flow due to changes in the riverbed. You might further study how the river affects the climate, possibly inducing changes in rainfall that in turn have an impact on the water flowing into the river. And yet, when you have delved down into all the technical hydrological details, all rivers still consist of water flowing downhill.
It was in that sense that I alluded to microevolution and macroevolution being the same basic process. Evolution is a process of change in the distribution of alleles, coupled with natural variations within the pool of available alleles and with the influence of environmental conditions on the selection of which alleles, if any, come to predominate within the population. Biologists are interested in breaking down this overall process into specialized submechanisms, and studying the factors and processes that produce certain specific types of variation under certain specific sets of conditions, and yes, in that particular technical discussion, you can make a technical distinction between microevolutionary processes and macroevolutionary processes. Such distinctions are of no use to evolution-deniers, however, because even here, we’re not talking about the kind of difference that would make microevolution possible while ruling out macroevolution.
In order to deny that macroevolution is possible (as Geisler and Turek attempt to do), creationists need at least one of two things: either a distinct mechanism for macroevolutionary changes, and/or a standardization mechanism which would triple the amount of genetic information required for each inheritable characteristic. Let’s take these one at a time.
Natural changes are the raw material of evolution. Mutations are the most famous source of natural variations, but there are others, which I’m not going to delve into here. The point is that these variations are all microvariations. There is no macrovariation that would allow, say, a cat to give birth to a horse. There may be subsequent specific processes that operate on these microvariations to produce macroevolutionary changes in the population(s) as a whole, but the fundamental basis for these changes necessarily involves the accumulation of microvariations passed from one generation to the next. Hence, even macroevolution is necessarily the accumulation of microevolutionary changes.
Failing a separate and distinct mechanism for macrovariations, the creationist can turn to the idea of genetic “barriers”—some kind of genetic standard that defines what the limits for a “kind” are, plus some sort of mechanism for enforcing those limits. The problem with this approach (apart from the fact that there is absolutely no scientific evidence or hypothetical mechanism for it) is that it requires each inheritable characteristic to have triple the genetic information required to describe the characteristic.
If a kind is allowed to have only a certain range of skin colors, for instance, the “skin color” gene must have not only the value of the current individual’s color, but also the minimum and maximum ranges that the kind is allowed to have. And even then, what happens if a mutation moves the skin color outside that range? You also need a mechanism for detecting the violation, and repairing it.
That’s a vastly oversimplified description, of course, but I think you get my drift. You could reduce the requirements somewhat by not allowing any variation at all, and requiring each characteristic to be an exact clone of the ancestral characteristic, but what about mutations? And even if you had a mechanism for detecting and repairing variations from the standard, what’s to prevent the mechanism itself from mutating? And even if you could propose a hypothetical self-repairing mechanism for maintaining an independent set of standards, where is there any evidence that any such mechanism exists and operates the way creationists need it to? And why, incidentally, would a wise Creator deliberately afflict His creatures with mechanisms designed to make them less adaptable and thus more fragile and liable to extinction in a hostile and changing environment?
The “barrier” against macroevolution is simply wishful thinking on the part of creationists. It just one more ramification of God’s failure to show up in real life: believers who are looking for evidence of His existence have to go all the way back to ancient prehistory to try and find something technical enough and obscure enough that they can say foolish things about it in order to create a pretext for claiming that divine intervention is necessary. That’s why so many devout believers (myself included) begin their journey away from Christian faith by taking a hard, honest look at creationism.