10. The myth of 1%
As if trying to suggest that those who question human-chimp common ancestry are ignorant, PBS asserts that "a schoolchild can cite the figure perhaps most often called forth in support of [human/chimp common ancestry]--namely, that we share almost 99 percent of our DNA with our closest living relative, the chimpanzee." Such an argument raises two questions:
human-chimp genetic differences.
(1) Is the 99% Human/Chimp DNA-similarity statistic accurate? While recent studies have confirmed that certain stretches of human and chimp DNA are on average about 1.23% different, this is merely an estimate with huge caveats. A recent news article in Science observed that the 1% figure "reflects only base substitutions, not the many stretches of DNA that have been inserted or deleted in the genomes."1 In other words, when the chimp genome has no similar stretch of human DNA, such DNA sequences are ignored by those touting the statistic that humans and chimps are only 1% genetically different. For this reason, the aforementioned Science news article was subtitled "The Myth of 1%," and printed the following language to describe the 1% statistic:
"studies are showing that [humans and chimps] are not as similar as many tend to believe";
the 1% statistic is a "truism [that] should be retired";
the 1% statistic is "more a hindrance for understanding than a help";
"the 1% difference wasn't the whole story";
"Researchers are finding that on top of the 1% distinction, chunks of missing DNA, extra genes, altered connections in gene networks, and the very structure of chromosomes confound any quantification of 'humanness' versus 'chimpness.'"
Indeed, due to the huge caveats in the 1% statistic, some scientists are suggesting that a better method of measuring human/chimp genetic differences might be counting individual gene copies. When this metric is employed, human and chimp DNA is over 5% different. But new findings in genetics show that gene-coding DNA might not even be the right place to seek differences between humans and chimps.
But there is a deeper question: (2) If humans and chimps were truly only 1% different at the genetic level, why should that demonstrate common ancestry? As noted in Slide 9, similarities in key genetic sequences may be explained as a result of functional requirements and common design rather than mere common descent. We might reasonably ask the evolutionist why the 1% difference value is considered powerful evidence for Darwinian evolution, and at what point does the comparison cease to support Darwinian evolution? What about 2% different? 3%? 5%? 10%? Is there an objective metric for falsification here, or is PBS putting forth a fallacious argument for human / chimp common ancestry?
Intelligent design is certainly compatible with human/ape common ancestry, but the truth is that the percent difference says nothing about whether humans and chimps share a common ancestor. The percent genetic similarity between humans and apes does not demonstrate Darwinian evolution, unless one excludes the possibility of intelligent design.
Just as intelligent agents 're-use' functional components that work over and over in different systems (e.g., wheels for cars and wheels for airplanes), genetic similarities between humans and chimps could also be explained as the result of the re-usage of common genetic programs due to functional requirements of the hominid body plan.
1. Jon Cohen, "Relative Differences: The Myth of 1%," Science, Vol. 316:1836 (June 29, 2007).