Discovery Institute, primate limbs, and “junk DNA”

In his September 24, 2008 post entitled “Study Challenges Two Icons of Evolution: Functional Junk DNA Shows “Surprising” Genetic Differences Between Humans and Apes,” Casey Luskin shows us just how much he really is out of touch with molecular biology and modern evolutionary theory.  He refers to an interesting study that seems to have found at least one of the reasons why there is such a difference in human limbs compared to other primates.  This article was published in the September 5th issue of Science.  Luskin somehow thinks these findings go against evolutionary theory.  They are perfectly consistent with the theory, as you will see below.

Luskin promotes the idea that scientists still believe that all the sequence that does not directly code for a protein is “junk.” The article of which he refers made a discovery in a region which may have once been considered “junk,” but not for a long time.  Scientists have known that DNA that is far away from a gene (thousands of base pairs) can directly regulate its function for decades. Other regions are believed to provide structural functions or regulate a gene that is nowhere nearby (see siRNA). This stuff widely known and Luskin is either lying or is willfully ignorant.  I also want to put some blame on the people who are responsible for the Yale press release. They are helping perpetuate this myth of “junk DNA,” but Luskin should know better as a person heavily involved in the evolution/ intelligent design debate.

To make his point about how “junk DNA” is still used as an “icon” for evolution, Luskin quotes a human physiology textbook by Willam McArdle et al. (emphasis mine):

“junk DNA” “is considered defective” and are “inherited sequences [that] perform no currently known ‘genetically useful’ purpose, yet they remain part of the chromosomes.”

Forget that the book is not an evolutionary biology textbook or even a molecular biology textbook. Did you notice the qualifier “not currently known?” Once a stretch of DNA is found to have a function, then it isn’t considered “junk” anymore.  Yet, Luskin still takes the stand that finding anything important in what he calls “junk DNA” discredits evolution.  Nothing could be further from the truth.

Here is the meat of Luskin’s argument:

Most studies that have claimed that humans and apes have nearly identical genomes have primarily looked at the gene-coding portions of the genome, not the non-coding DNA (formerly claimed to be “junk”). Perhaps as biologists study the non-coding portions of our genome, they will find evidence that challenges two Darwinists icons: Not only does “junk” DNA have function, but humans aren’t as genetically similar to apes as was once thought.

We have already convered that “junk DNA” is a misnomer and he even says that it was “formerly claimed.”  So this being an “icon” of evolution doesn’t really make any sense.  But what about his argument that we “aren’t as genetically similar to apes?”

The article in question seems to promote the idea (or at least Luskin’s take on it) that humans and chimpanzees aren’t as similar as once thought due to the press release saying that the finding“was especially surprising, as the human and chimpanzee genomes are extremely similar overall.”

Lets do some overly simplified math to see if these findings contradict evolution. The region in question (HACNS1) is 546 bases long. They found 16 differences between humans and chimpanzees. So if we do the math (16/546), we find that there is approximately a 3% difference between the human and chimpanzee HACNS1 region. This percentage is exactly the same as the overall difference between the two organisms and matches nicely with the rate of mutation predicted by evolutionary theory since the time of human-chimpanzee split (~6 million years ago).

If the math all lines up, why is this finding surprising? It turns out that there are certain regions of DNA that are so critical that mutations in these regions would be devastating for their function. Only rare and beneficial mutations would be allowed to persist. In fact, this region is highly conserved throughout land animals and it has 4X as any mutations as would be expected based on this evolutionary constraint.

Tracer showing human expression in mouse

Tracer showing human expression by HACNS1 in mouse limb

The end result of these mutation seems to effect the way humans thumbs, wrists, and other limb characteristics develop. In fact, when the scientists put the human DNA region in question in mice with a tracer (see image) and compared it to chimpanzee region, they saw a stark contrast in the levels of the tracer between the two organism’s DNA. The regions where the tracer was observed corresponds to areas that seem to be responsible for both the greater flexibility of the human thumb and wrist. Of course more study needs to be done on the subject, but It does show that this small region could be important.

Everything in the report is consistent with evolutionary theory, despite what Luskin says. If anything it strengthens the argument that small changes (12 changes in 3 billion) between humans and chimpanzees can go a long way. Remember that the “icons” that Luskin speaks of are really strawmen created to divert unsuspecting readers away from the real arguments and evidences.

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2 Responses

  1. Thanks for this nice take-down. Luskin shouldn’t write about science he just can’t get it right.
    Have you seen his latest piece yet? Now he’s talking about Per Ahlberg’s new Panderichthys article. Obviously, because Panderichthys is an even better example of transitional features between fish and tetrapodes than Tiktaalik (in Ahlberg’s view?) a) scientists were lying about Tiktaalik being transitional, b) Luskin was right about Tiktaalik and c) there still are no good transitional fossils. Deluded.

  2. JLT,

    Thanks for the heads up. I will have to check it out.

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