Posts Tagged ‘chimp vs human’


Chimp vs Human DNA- The “Ninety-Eight Percent” Myth

Monday, August 9th, 2010

As we enter the month of August, it’s time once again for students to head back to school.  That being the case, there’s a good chance that in science classes all across the country, as teachers cover the topic of evolution, sooner or later they will make mention of the “98 percent similarity” between human DNA and chimpanzee DNA, thus implying common ancestry.  Over the past several years, this idea of 98 percent similarity has been repeated so many times that it is now widely accepted by most people as a “scientific fact.”  But is that really the case?

To begin with, it’s really important to understand that this whole idea of comparing DNA can be rather tricky business and we must exercise a great deal of caution when it comes to the conclusions that we draw from the data and how we interpret that data.  For example, compare the two sentences below:

“You are going on an all-expense-paid trip to the Caribbean aboard a luxurious cruise ship.”

“You are NOT going on an all-expense-paid trip to the Caribbean aboard a luxurious cruise ship.”

Even though these two sentences have 98 percent homology (similarity), they have  opposite meanings- the difference between going and not going!  In a similar way, since DNA is all about information, a high degree of similarity between two DNA sequences does not necessarily mean that they have the same meaning or function.

Another pitfall that we must avoid in comparing DNA is that we have to be careful not to assume that genetic similarity necessarily points to some sort of ancestral-descendant relationship or relatedness.  After all, some studies have shown that humans and daffodils share a 35 percent genetic similarity.  But I don’t think that anyone is prepared to interpret that data to mean that humans are “related to daffodils” or that humans are “over one-third daffodil.”

Getting back to the claim that humans and chimps are 98 percent similar, the most damaging evidence of all was revealed in more recent studies as reported a few months ago in the journal Nature.  (see Nature. 463 (7280):536-539)  The article’s title alone speaks volumes about what researchers found: “Chimpanzee and Human Y Chromosomes are Remarkably Divergent in Structure and Gene Content.”  In other words, chimp and human Y chromosomes are surprisingly different.  The results of this more recent research contradicts the initial findings from the 2005 chimpanzee genome project which ultimately led to the idea of 98 percent similarity.  As it turns out, one of the underlying problems with the 2005 study was that it was extremely biased toward an evolutionary view.  Rather than trying to determine whether or not chimps and humans are related, researchers in the 2005 study began with the assumption that chimps and humans are related.  When they began the process of assembly and orientation of the sequences gathered from the chimpanzee genome, they did so based on a map of the human genome rather than basing it on a map of the chimpanzee genome.  Taking this approach allowed their evolutionary bias to influence the outcome of the study.

So, the long and short of all of this is that the idea of “98 percent similarity” is a myth.  According to the latest, more accurate study, the overall similarity turned out to be 70 percent or less.  It will be interesting to see whether or not this latest information is mentioned at all in our high school science classes this year.  If not, it should be a reminder to all of us that those who knowingly disallow such information are more interested in pushing their ideology than they are about doing good science.

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