The Evolutionary Gorilla In The Room

-Submitted by David Drumm (Nal), Guest Blogger

One common tactic in the creationist’s war against evolution is to falsify evolution by demonstrating a counterexample. If such a counterexample existed, it would indeed spell the demise of evolution. The Precambrian Rabbit would be such a counterexample. After failing to find even one counterexample, some creationists have given up trying to falsify evolution and now seek to disabuse evolution by claiming it is not falsifiable. Other creationists, unable to falsify evolution, get all metaphysical and point out that the principle of falsifiability is not falsifiable.A recent paper in the journal Nature, Insights into hominid evolution from the gorilla genome sequence, after sequencing the western lowland gorilla genome, it was found that “in 30% of the genome, gorilla is closer to human or chimpanzee than the latter are to each other.”

Creationists pounced, noting that depending on which DNA fragment is used for analysis, humans are more closely related to gorillas than to chimpanzees. Although this was termed “Bad News” for evolution, it would have been worse news for probability theory. While the genomes of humans and chimpanzees show a mean genetic difference of 1.37%, and a 1.75% difference between humans and gorillas, the key word is “mean.” These probabilities do not imply that there is a uniform genetic difference across all genes. Of the tens of thousands of genes, some are more similar and some are less similar. On average, humans are more closely related to chimpanzees than to gorillas.

On the genetic path from our Most Common Recent Ancestor (MCRA) to humans and gorillas, different genes mutated at different times. Although cladograms, like the one below for Humans, Chimpanzees, Gorillas, and Orangutans, show a single branch to each species, this does not imply that all the genetics differences occurred simultaneously. One would have to be a creationist to believe that all the mutations occurred simultaneously.

One would also expect to find that certain DNA fragments would more similar between humans and orangutans. This is exactly what was found in this report, based on a complete orangutan genome, published in Genome Research, in which the authors said that “in about 0.5% of our genome, we are closer related to orangutans than we are to chimpanzees.”

Even the well-funded BioLogos, a group dedicated to trying to accommodate Christianity and science, sees the errancy of these arguments:

This is exactly what one expects from the species tree: humans and chimps are much more likely to have gene trees in common, since they more recently shared a common ancestral population (around 4-5 million years ago). Humans and orangutans, on the other hand, haven’t shared a common ancestral population in about 10 million years or more, meaning that it is much less likely for any given human allele to more closely match an orangutan allele.

Creationists are engaged in a desperate, but lucrative, attempt to pull a Precambrian Rabbit out of their hat. This attempt is particularly pathetic.

H/T: Pharyngula, John Wakeley (pdf), Pharyngula.