Finally, they’ve come right out and said what we knew all along: most of our DNA has to be junk. I guess that’s progress, but they’re not doing a good job of explaining it.
After 20 years of biologists arguing that most of the human genome must have some kind of function, the study calculated that in fact the vast majority of our DNA has to be useless. It came to this conclusion by calculating that, because of the way evolution works, we’d each have to have a million children, and almost all of them would need to die, if most of our DNA had a purpose.
None of the biologists I know have been arguing for ubiquitous functionality, but I know they’re out there, so that’s kind of a strange opening: it’s as if the only way they know how to frame the story is as some kind of real conflict (see also every NS article about evolution vs. creationism). I don’t know where the 20 year timing comes from, either. JBS Haldane died 53 years ago, and he worked out this argument long before his death.
But worst of all, they just plop out this claim that we’d “each have to have a million children, and almost all of them would need to die, if most of our DNA had a purpose”. OK. Reading this as a naive layman, WHY? They present the conclusion with none of the evidence or logic behind it; there is no explanation here. The key part of the story that Dan Graur explained is that we know the mutation rate of human genes, and we can calculate the cost to the population of carrying around suboptimal genes, and we can estimate how many children you’d have to have to compensate for that load of mutations, and the load is going to depend on how many genes are present. It’s easy to put an upper bound on the number of genes we have, given our mutation rate and how many children an individual can have (hint: there’s no way you can have a million kids.)
The logic is clear and convincing, but you have to present it if you’re trying to communicate the science.
I feel like I’m grading an exam. Yes, you got the correct answer, but I’m not convinced that you understand how you arrived at it, and aren’t just regurgitating something you memorized.