Our Top 10 Evolution-Related Stories: #5, Publication of the Gorilla Genome
Editor's note: A memorable and unwelcome news development for Darwinian evolutionists this year was the publication of the gorilla genome. Casey Luskin gave us his report and analysis ("30% of the Gorilla Genome Contradicts the Supposed Evolutionary Phylogeny of Humans and Apes").
A whopping 30% of the gorilla genome -- amounting to hundreds of millions of base pairs of gorilla DNA -- contradicts the standard supposed evolutionary phylogeny of great apes and humans. That's the big news revealed last week with the publication of the sequence of the full gorilla genome. But there's a lot more to this story.
Eugenie Scott once taught us that when some evolutionary scientist claims some discovery "sheds light" on some aspect of evolution, we might suspect that's evolution-speak for 'this find really messed up our evolutionary theory.' That seems to be the case here. Aylwyn Scally, the lead author of the gorilla genome report, was quoted saying, "The gorilla genome is important because it sheds light on the time when our ancestors diverged from our closest evolutionary cousins around six to 10 million years ago." NPR titled its story similarly: "Gorilla Genome Sheds Light On Human Evolution." What evolutionary hypothesis did the gorilla genome mess up?
The standard evolutionary phylogeny of primates holds that humans and chimps are more closely related to one-another than to other great apes like gorillas. In practice, all that really means is that when we sequence human, chimp, and gorilla genes, human and chimp genes have a DNA sequence that is more similar to one-another's genes than to the gorilla's genes. But huge portions of the gorilla genome contradict that nice, neat tidy phylogeny. That's because these gorilla genes are more similar to the human or chimp version than the human or chimp versions are to one-another. In fact, it seems that some 30% of the gorilla genome contradicts the standard primate phylogeny in this manner. New Scientist explains:
But despite the ancient split, the remaining 30 percent of [the gorilla's] genome turned out to be more closely related to humans or chimp than those species are to one another...Nature news put it this way:
(Sara Reardon, "DNA from the last of the great apes decoded," New Scientist, March 10-16, 2012, p. 12)
But the genome sequencing has thrown up surprises, too. The standard view of the great-ape family tree is that humans and chimps are more similar to each other than either is to the gorilla -- because chimps and humans diverged more recently. But, 15% of human genes look more like the gorilla version than the chimp version.Scally's interview with NPR stated:
And what we see that as is in fact this 15 percent figure that you may have mentioned or that people might have seen, which is that humans are actually closer to gorillas in 15 percent of their genome, of the human genome. So overall we're closer to chimpanzees, and 70 percent of our genome is closer to chimpanzees. That's consistent with the speciation of the species tree.Likewise, the technical paper in Nature stated: "In 30% of the genome, gorilla is closer to human or chimpanzee than the latter are to each other." As a result, now they must qualify assertions that chimps are our "closest" relatives, as the paper stated "Molecular studies confirmed that we are closer to the African apes than to orangutans, and on average closer to chimpanzees than gorillas." (emphasis added) "On average," of course, is wiggle-language, because huge portions parts of our genomes don't fit with the standard evolutionary phylogeny. As one of the researchers put it, "We can't just conform to a simple tree on a gene-by-gene basis."
But there are these regions all across the genome where the ancestry is different, and that amounts to 15 percent where humans and gorillas are closest and then another 15 percent where chimpanzees and gorillas are closest.
As always, they try to explain why hundreds of millions of base pairs in the gorilla genome contradict the standard phylogeny. As we saw in an ENV post from last year titled, "Study Reports a Whopping '23% of Our Genome' Contradicts Standard Human-Ape Evolutionary Phylogeny," their explanation is that interbreeding between populations of chimps, humans, and gorillas after the initial splits of these lines caused different genes to become fixed in different lineages at different times. Called incomplete lineage sorting, it provides a convenient after-the-fact explanation for why different genes carry different phylogenetic signals. Of course, this is merely an ad hoc hypothesis invoked to explain away inconvenient data which contradicts the standard phylogeny.
The bottom line is that the gorilla genome has confirmed that there is not a consistent story of common ancestry coming from the genomes of the great apes and humans. Hundreds of millions of base pairs in the gorilla genome conflict with the supposed phylogeny of great apes and humans. They might think their explanation salvages common ancestry, but clearly the gorilla genome data badly messes up the supposedly nice, neat, tidy arguments which they use to claim humans are related to the great-apes.
Genes Don't Talk
What's also interesting is that one of the gorilla genes which conflicted with the standard primate phylogeny was highly similar to a human gene, thought by evolutionists to be involved in the origin of human speech. But obviously gorillas don't talk. So if this gorilla gene is highly similar to the human version, it stands to reason that those human genes may not be as important for the evolution of speech after all. As Nature news explained:
Much of the 15% is in sections of the genome that do not code for proteins. But the researchers also looked at functional gene changes. They found that certain genes -- including some involved in hearing and brain development -- had gone through more rapid changes than expected in both the gorilla and human lineage.Gorilla Genome Researchers Fall Back to Weaker Arguments for Common Ancestry
Some of these rapid changes are puzzling: the gene LOXHD1 is involved in hearing in humans and was therefore thought to be involved in speech, but the gene shows just as much accelerated evolution in the gorilla. "But we know gorillas don't talk to each other -- if they do they're managing to keep it secret," says Scally.
This weakens the connection between the gene and language, says Enard. "If you find this in the gorilla, this option is out of the window."
Since the gorilla genome didn't fit nicely with the standard phylogeny of higher primates, evolutionary scientists sought to put some spin on the situation to support common ancestry. They thus fell back to making the old "we're 98% ape" argument:
"The big picture is that we're perhaps 98 percent identical in our sequences to gorillas. So that means most of our genes are very similar, or even identical to, the gorilla version of the same gene," said Chris Tyler-Smith, a geneticist at Wellcome Trust.Of course, the "big-picture" implication that Tyler-Smith wants you to take is that if we're 98% genetically similar to gorillas, then we must be related to them. Of course this argument is full of logical fallacies and factual inaccuracies.
First, we're less than 98% similar to chimpanzees, which are supposedly "on average" more closely related (e.g. genetically similar) to humans than gorillas. So Tyler-Smith has overstated the percent genetic similarity between humans and gorillas.
Second, even if humans and gorillas actually were 98% genetically similar, why should that demonstrate common ancestry? We might reasonably ask the evolutionist why 98% similarity is considered powerful evidence for common ancestry, and at what point does the comparison cease to support common descent? What about 97% different? 95%? 90%? 80%? Is there an objective metric for falsification here, or is Tyler-Smith implying a fallacious argument for human / gorilla common ancestry?
Finally, intelligent design is certainly compatible with human/gorilla common ancestry, but the percent difference says nothing about whether humans and gorillas share a common ancestor. 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, or keyboards for computers and keyboards for cell phones), genetic similarities between humans and other apes like gorillas could also be explained as the result of the re-usage of common genetic programs due to functional requirements of the hominid body plan. The percent genetic similarity between humans and apes does not demonstrate Darwinian evolution, unless one excludes the possibility of intelligent design.