I want to make a quick point about how evolution works and how it does not. The reason is that two stories about non-coding DNA posted today include a major misconception about evolution. Unfortunately, this is a misconception attributed in the articles to biologists, so I can only imagine what the state of comprehension is among non-scientists.
The distinction is between “because” and “so that”. In evolution, things evolve “because,” meaning that there are causes and effects that can be identified. Why are some strains of bacteria resistant to antibiotics? Because a mutation that occurred that happened to be beneficial under the conditions of antibiotic treatment became common in the population over the course of several generations. By contrast, things do not evolve “so that”. Bacteria do not experience mutations so that they will become resistant to antibiotic agents.
Why is there so much non-coding DNA? Because transposable elements spread, or because there are accidental duplications that are not eliminated by selection, or because of the interaction of some other mutational processes and their consequences (or lack thereof). So much non-coding DNA did not evolve so that it might someday be useful, or so that it could be coopted when needed, or so that evolution would have more potential in the form of genetic raw materials.
So why, then, do we see quotes like these?
“I’ve stopped using the term [‘junk’],” Collins said. “Think about it the way you think about stuff you keep in your basement. Stuff you might need some time. Go down, rummage around, pull it out if you might need it.”
“It is not the sort of clutter that you get rid of without consequences because you might need it. Evolution may need it,” [Collins] said.
That little extra padding might be just what an animal needs to adapt to some unforeseen circumstance, the researchers said. “They may become useful in the future,” Birney said.
The latter quote by Ewan Birney illustrates the problem that can arise when a detailed, nuanced discussion is summarized into a short soundbite. I know this from experience, and I suspect that this is what has happened here, given how his very reasonable interpretation is paraphrased in New Scientist ‘Junk’ DNA makes compulsive reading:
Birney says that the additional switches may be mutations that appear by accident and then generate new slugs of RNA, but because they are produced randomly, most are evolutionarily neutral ‘passengers’ in the genome. There might be rare occasions, however, when a new RNA does confer an advantage.
Collins, on the other hand, seems to have said his bit to two different reporters, so I strain to give him the benefit of the doubt on this one. When I began this blog, I did not think I would be pointing out obvious misconceptions about evolution, genomes, and DNA as propagated by the likes of Collins or Nature. But here we are.