When an anti-evolutionist attempts to publicly “explain” a scientific paper, it usually signals two things: you should read the paper for yourself, and you should not be surprised to find that the creationist “explanation” misrepresents what the paper really says. A new blog post by Paul Nelson is no exception. Nelson, descending from the (relative) intellectual heights of the Discovery Institute to join the crowd at Dembski’s Whine Cellar, tells his readers that scientists did not grasp the true point of a 1975 paper because they did not read it all the way through.
The paper in question is a relatively famous one – it’s a paper in Science by Mary-Claire King and Allan Wilson that compared the available measures of genetic difference between humans and chimps with what was known about the morphological, behavioral, and cultural differences between the two species. King and Wilson, in this paper, calculated that there was a 1% genetic difference between humans and chimps, and that this difference is not enough to account for how different the two species really are. Nelson claims that scientists focused on the first finding because it was reported early in the paper, and missed the second part because it came later, after us lazy lab boys had given up on reading. (Nelson apparently believes that scientists share his work ethic.)
But one cannot hold King and Wilson responsible for what lazy readers did with their powerful paper. The “one percent” message comes on the second page of the paper (p. 108). If being mostly chimp, genetically speaking anyway, is what matters to a reader, chances are he’ll do what Simon and Garfunkel sang about in “The Boxer” — “a man hears what he wants to hear, and disregards the rest” — and stop reading.
The real message of King and Wilson 1975 arrives later in the paper, where casual readers don’t bother to follow:
The molecular similarity between chimpanzees and humans is extraordinary because they differ far more than sibling species in anatomy and way of life. Although humans and chimpanzees are rather similar in the structure of the thorax and arms, they differ substantially not only in brain size but also in the anatomy of the pelvis, foot, and jaws, as well as in relative lengths of limbs and digits. Humans and chimpanzees also differ significantly in many other anatomical respects, to the extent that nearly every bone in the body of a chimpanzee is readily distinguishable in shape or size from its human counterpart. Associated with these anatomical differences there are, of course, major differences in posture…, mode of locomotion, methods of procuring food, and means of communication. Because of these major differences in anatomy and way of life, biologists place the two species not just in separate genera but in separate families. So it appears that methods of evaluating the chimpanzee-human difference yield quite different conclusions. (p. 113, footnote numbers omitted; emphasis added)
Strangely enough, there is another, shorter, passage that makes essentially the same point found elsewhere in the paper. Nelson didn’t quote this one – I had to read the paper to find it.
The intriguing result, documented in this article, is that all the biochemical methods agree in showing that the genetic difference between humans and the chimpanzee is probably too small to account for their substantial organismal differences.
That quote is found on page 107 of the paper. That’s the first page of the article, one page prior to the mention of 99% similarity.
Reality, as is so often the case, simply does not match Nelson’s assertions here. The truth of the matter is that the King and Wilson paper did not become a landmark simply because they reported on the genetic similarity between our species and our close cousins. As good scientists are prone to do, King and Wilson did not simply report on what they saw. They took what they saw and understood then – in 1975 – and used it to make predictions about what they (or others) would find later on.
In 1975, scientists had only a very limited number of methods available for measuring genetic distance. They could look at differences in the proteins produced by genes a couple of different ways. They could also very crudely assess the degree of similarity between the DNA of two species by examining differences in melting temperature. The methods that evolutionary geneticists and molecular ecologists normally use (and take for granted) today were still a decade or more away.
Using the tools available, King and Nelson found that most chimp proteins are virtually identical to their human counterparts, and that the DNA of chimps matched the DNA of humans very closely in melting temperature experiments. At the same time, we know that there are some rather substantial differences between humans and chimps – besides the obvious differences in language, cultural behaviors, and intelligence, there are also significant (and obvious) differences in bone structure and overall physical appearance. The differences that they found in the proteins isn’t enough, they believed, to explain the differences. That, in turn, lead them to make the following prediction (also found on the first page of the paper):
In order to explain how species which have such similar genes can differ so substantially in anatomy and way of life, we review evidence concerning the molecular basis of evolution at the organismal level. We suggest that evolutionary changes in anatomy and way of life are more often based on changes in the mechanisms controlling the expression of genes than on sequence changes in proteins. We therefore propose that regulatory mutations account for the major biological differences between humans and chimpanzees.
That prediction, by the way, seems to have been on the money. The more we learn about genomes, about the way genes work, and about the similarities and differences between us and the chimps, the more accurate the prediction appears.
A news story in this week’s Science (also cited by Nelson) points out that:
When King [yes, that's the same King that wrote the other paper] and the rest of the researchers in the Chimpanzee Sequencing and Analysis Consortium first detailed the genome of our closest relative in 2005, they simultaneously provided the best validation yet of the 1% figure and the most dramatic evidence of its limitations. The consortium researchers aligned 2.4 billion bases from each species and came up with a 1.23% difference. However, as the chimpanzee consortium noted, the figure reflects only base substitutions, not the many stretches of DNA that have been inserted or deleted in the genomes. The chimp consortium calculated that these “indels,” which can disrupt genes and cause serious diseases such as cystic fibrosis, alone accounted for about a 3% additional difference (Science, 2 September 2005, p. 1468).
Entire genes are also routinely and randomly duplicated or lost, further distinguishing humans from chimps. A team led by Matthew Hahn, who does computational genomics at Indiana University, Bloomington, has assessed gene gain and loss in the mouse, rat, dog, chimpanzee, and human genomes. In the December 2006 issue of PLoS ONE, Hahn and co-workers reported that human and chimpanzee gene copy numbers differ by a whopping 6.4%, concluding that “gene duplication and loss may have played a greater role than nucleotide substitution in the evolution of uniquely human phenotypes and certainly a greater role than has been widely appreciated.”
Nelson may claim this as evidence that macroevolution is an “open puzzle,” but I suspect that most of us are going to see it for what it is – both the vindication of a past prediction, and an indication that we’re on the right track for learning more about what makes humans human and chimps chimp.