Junk DNA is Not Junk

When I was young, I often encountered the notion that we only use 10 percent of our brains. I can't recall the science behind this, but it seemed so convincing that even people who found it hard to believe had trouble getting around it. In my memory I was always dubious of this notion, although perhaps I flatter myself. I certainly did give the matter much thought. It is not true, of course; MRI studies show us using every part of our brains all the time. In fact, this was one of the stupidest scientific notions ever advanced. Our brains use an enormous amount of energy, and it is simply bizarre to think that evolution could have crafted something so utterly wasteful that served no purpose whatsoever.

When people started claiming, 15 or 20 years ago, that 98% of our DNA is "junk," this sounded to me exactly like the claim that we only use 10% of our brains. Why would evolution create a system capable of storing an astonishing amount of information, and devote so much care to preserving it, copying it, protecting it from attacks, and so on if it serves no purpose? Our cells are models of efficiency; they have no parts lying around that are not being used for something. When cellular machinery is no longer needed for one purpose, it is turned to some other purpose. All of that magnificent DNA must, I have long been certain, be doing something.

Now the molecular geneticists have finally started figuring out what all that "junk" DNA is for. It may be true that only 2% of our DNA codes for genes, but at least 75% of it is "active" in some way. A lot of it probably helps determine when the genes are turned on and off, and in what sequence. Some of it probably does other things.

The deeper lesson here is that the right way to think about living organisms is in evolutionary terms. If something does not make sense in evolutionary terms, it is probably wrong. Brain scientists were certain we weren't using big regions of our brains, even though that makes no evolutionary sense; they were wrong. Molecular geneticists were sure 98% of DNA was inactive, even though that makes no evolutionary sense; they were wrong. In biology, evolution is the master doctrine, without which nothing else can be properly understood.