From a technical scientific perspective, the degree of genetic similarity between humans and chimps seems to be of questionable relevance when one is trying to determine whether two species share a Darwinian past. After all, designers regularly re-use parts that work, especially programming components, so there’s no reason to presume that mere genetic similarity necessarily implies common descent over common design.

Moreover, even if such genetic similarities were to imply common ancestry, they don’t demonstrate a plausible stepwise Darwinian evolutionary pathway. Nonetheless, on a rhetorical level, the claim that humans and chimps are 99% the same is a powerful emotional argument aiding those seeking to evangelize for Darwinism. For example, last year a cover story of Time magazine proclaimed: “chimps are our nearest evolutionary cousins, roughly 98% to 99% identical to humans at the genetic level.” In his 2002 book, What it means to be 98% chimpanzee, University of North Carolina Charlotte anthropologist Jonathan Marks (an avowed evolutionist himself) laments how Darwinian scientists abuse this statistic:

[W]hy should it really matter whether we are descended from arboreal hairy primates or not? … The reason it matters to so many people is that scientists have made it matter, and they’ve done so in the worst possible way. They’ve taken a proposition …”We are descended from apes”–and stretched it into a series of additional propositions, often both authoritative and odious. Thirty years ago, in a widely read scientific-philosophical work called Chance and Necessity, the French molecular biologist Jacques Monod argued that evolution shows life to be meaningless.

(Jonathan Marks, What it means to be 98% chimpanzee, pg. 281 (University of California Press, 2002).)

Thus, it seems that many committed Darwinists have invested much rhetorical capital into the allegedly near-100% degree of genetic similarity between humans and apes, and Marks recounts they have even used it to argue that “life [is] meaningless.”

But what would people think about evolution if Time magazine instead printed the following hypothetical story:

“Chimps are our nearest evolutionary cousins, and we used to think they were 98% to 99% identical to humans at the genetic level, but since we’ve sequenced the chimp and human genomes, scientists are calling that statistic a ‘myth’ because improved methods of comparing genomes reveal that chimps are only 94% to 95% similar to humans.”

The Darwinist argument loses some of its punch, doesn’t it? Yet this hypothetical headline above seems entirely appropriate in light of the findings reported in my blog post from this past weekend about a Science news article entitled “Relative Differences: The Myth of 1%.” This article reported, “Genomewise, humans and chimpanzees are quite similar, but studies are showing that they are not as similar as many tend to believe” and went on to report that recent studies show that “human and chimpanzee gene copy numbers differ by a whopping 6.4%.” It sounds like the kind of report that might cause the human-chimp similarity argument to lose some of its punch.

Soon after my post went live, the author of the “The Myth of 1%” article, Jon Cohen, contacted me with various concerns about my blog post. To help readers explore this dialogue, below I reprint Jon Cohen’s article to me in full (with permission), and my response to Mr. Cohen can be read here.

From: Jon Cohen [snip]
Sent: Saturday, October 20, 2007 12:05 PM
To: Casey Luskin
Cc: [Snip]
Subject: Errors in your posting

Mr. Luskin,

I wrote the Science news article that you refer to in your recent posting on the Discovery Institute’s “Evolution News and Views.”

Given that “misreporting of the evolution issue is one key reason” for that site, which complains that “much of the news coverage has been sloppy, inaccurate, and in some cases, overtly biased,” I wanted to point out that your own post contains several errors and apparent misunderstandings. I realize that you are largely reporting what others have written, but you do it selectively and out of context–and you also fail to scrutinize what the original reports said.

As I wrote in my article, chimps and humans do differ genetically by more than 1%, but our genes–in contrast to what the Scientific American posting states–are only 1.23% different. The bulk of the differences between chimps and humans exist in noncoding regions of the genome that regulate our genes and in gene copy number variation/segmental duplication, which ultimately determine how much product (typically protein) they produce. You also state that my article “reports” that copy numbers differ by 6.4%. Not only does this misleadingly imply that humans thus differ from chimps by 6.4% (it’s probably closer to 5%), you fail to note that my article was not the source of this figure: I was citing a report that was done by a computational genomics researcher. In other words, it’s a model, which is another way of saying it’s an estimate, not a hard fact. (The 1.23% is a hard fact: It’s based on sequencing the entire human genome and the chimpanzee genome.)

The claim that humans are as different from each other as was previously thought we were different from chimps also is misleading and inaccurate. No credible study that I know of ever suggested that one human’s genes differ from another human’s gene by 1.23%. The Scientific America posting–which is referring to an AP story in USA Today that’s referring to the PLoS Biology paper about Craig Venter’s genome–does not explain that Venter reported a 0.5% difference between his inherited genome from his mother and father, which once again is measuring not simply gene differences but differences in noncoding regions that include inserts and deletions (that may sometimes contain copied or deleted genes or may impact regulation).

None of the original studies I cited in my article or Venter’s genome paper suggest in any way that their findings challenge Darwinian evolution, and I doubt that any of those researchers would support that conclusion from their data. And indeed, the fact that we differ genetically by more than 1%, largely for gene regulatory reasons, was predicted in Science more than 30 years ago (again as my article notes)–and the 1975 article was co-authored by one of the world’s leading evolutionary biologists at the time, Allan Wilson.

The bottom line is that your post is so distant from the sources that you have completely garbled the data to support Intelligent Design. It’s sloppy, inaccurate, and overtly biased.

Your are welcome to post my e-mail in its entirety, but given the errors that you made in your post by selectively quoting from other posts, please do not excerpt this for a public posting.

I’m also attaching original papers that discuss these issues. It’s complicated stuff, and I hope these papers help clarify the details.

Jon Cohen

My response to Mr. Cohen can be read here.