The majority of creationists freely admit the existence of biological variation, adaptation and speciation. But, how do they reconcile this with their rejection of evolution? A former young-Earth creationist walks us through the convoluted logic.
I've previously introduced David MacMillan, a former creationist blogger, who has begun writing a series of explainers to unravel these pseudo-scientific beliefs and highlight the challenges of debating creationist misconceptions.
Writing over at Panda's Thumb, MacMillan takes on the topic of microevolution:
The recent-creation model— particularly the belief that all extant life descended from a small group of "kinds" present on Noah's Ark which diversified into all families on Earth after a global flood— requires enormous adaptive variation and near-constant speciation. Creationists estimate that fewer than 10,000 pairs of land-dwelling, air-breathing animals on the Ark diversified to represent all families alive today. There are around 6.5 million land-dwelling species today, so millions of speciation events would have needed to take place over the past 44 centuries since their global flood.
As a side point: in order to go from 10,000 primordial "kinds" to 6.5 million species in less than 5000 years, the number of species would need to double every 385 years. If the rate of evolutionary development and speciation really were this rapid, few species would endure for more than four or five centuries without undergoing drastic and noticeable adaptation, and we would presently see about 45 new species emerging every single day. To explain this inconsistency, creationists will sometimes imagine an even more rapid period of hyper-evolution immediately following the Flood, after which adaptation and speciation would supposedly stabilize to their presently observed levels. Apart from being utter special pleading, this explanation is even more problematic: each species would have to undergo a speciation event every few generations. So creationists most certainly accept the existence of biological variation and speciation. Creationists call this rapid diversification from "kinds" down to modern species "microevolution." However, the mechanism they propose as the basis of "microevolution" differs broadly from the mechanism accepted and taught as part of the theory of evolution.
Creationist literature— particularly curriculum, though this is the rule in apologetics and journals as well— typically presents Mendelian inheritance as the sole mechanism for biological variation. Almost all biological variation is believed to come through this process: the recombination of whole genes (examples usually tracing the familiar-but-oversimplified dominant/recessive system) from parental chromosomes to produce offspring with a blend of traits from each parent. They propose that this new blend of pre-existing traits is subject to natural selection and can cause those traits (and their associated genes) to become more or less prevalent in the population as a whole. Eventually, the concentration of these genes in subsets of the population is expected to lead to a split and the emergence of a new species. Creationists also point out that the loss of genetic information due to mutation can produce similarly selectable results, accelerating the diversification process. However, they will invariably add that this process works in only one direction; mutations can remove genetic information, but they cannot (in the creationist mindset) add it.
The creationist model claims that the variation provided by Mendelian inheritance and genetic loss— this "microevolution" mechanism— is responsible for all the variation we ever observe in nature. They claim that this observed level of variation is sufficient for the diversification of the 10,000 kinds represented on the Ark, but – they claim – not sufficient to produce the new genetic information needed to produce all life from a single common ancestor (what they term "macroevolution"). By erroneously supposing that Mendelian recombination is the exclusive source of genetic variation, they neatly exclude any viable mechanism for universal common descent.
Correcting this misconception can be difficult. It is not enough to explain that macroevolution is the accumulation of microevolution over time, because creationists define these as two distinctly different processes. They actually are correct in arguing that their "microevolution" could never accumulate into "macroevolution" because their definition of "microevolution" is much more limited than we see in reality. They must be made to understand that the genetic variation we actually observe on a daily basis is fundamentally different than what their "microevolution" allows for.
The misconception depends on a lack of information about microbiology and sexual reproduction in general, but there is a conceptual foundation at play as well: the idea that God is the prime creator of information, including genetic information. This idea is philosophical: the assumption that no new information can arise without an intelligence.
[Via Panda's Thumb]