Larry Moran asks an interesting set of questions about human DNA:
How much of it could be removed without affecting our species in any significant way in terms of viability and reproduction? Or even in terms of significant ability to evolve in the future? In other words, how much is junk?
The options are:
- less than 10%
- between 11% and 49%
- between 50% and 74%
- between 75% and 89%
- 90% or more
I hope people take his poll, because I think it will be intriguing to see what most people think. However, I have to admit that I won’t really be able to vote, for the reason I outlined in the comments to his article:
I think this is where a distinction between nonfunctional and inconsequential is important [see Effect versus function for more details]. In terms of whether most DNA is functional, I would agree on the basis of what we currently know that much of it could be deleted in principle. However, this would also affect cell size, and therefore organs, and therefore organisms. And yet, I would not necessarily consider the influence of DNA amount on the cell as a function. It could very well be that there is upward pressure from transposable elements and other mechanisms that cause DNA to accumulate, and downward pressure against this accumulation through selection on organisms. The balance that has been reached is not necessarily adaptive for either side. However, deleting a lot of it could have impacts on development and morphology nonetheless. Maybe it would even be a beneficial change, maybe deleterious, but I can’t assume that there would be no effect.
In some ways, it’s a little like asking, how much of the bacteria in your gut could you kill without having an effect on your health? In principle, a lot of it is clearly not functional, and none of it is there just to function on your behalf. But if you cleared the gut of all bacteria, or even just the commensal and parasitic species, would there be no effect? And if there were adverse consequences, would you take this as evidence that all those bacteria had a function after all?