The only definitively nonfunctional DNA is that which has been deleted. “Nonfunctional DNA” is temporarily inactive legacy code which may at any time be restored to an active role.
In the context “how complicated is a human brain?”, DNA which is currently inactive does not count towards the answer.
That said (by which I mean “what follows doesn’t seem relevant now that I’ve realised the above, but I already wrote it”),
Is inactive DNA more likely to be restored to an active role than to get deleted? I’m not sure it makes sense to consider it functional just because it might start doing something again. When you delete a file from your hard disk, it could theoretically be restored until the disk space is actually repurposed; but if you actually wanted the file around, you just wouldn’t have deleted it. That’s not a great analogy, but...
My gut says that any large section of inactive DNA is more likely to become corrupted than to become reactivated. A corruption is pretty much any mutation in that section, whereas I imagine reactivating it would require one of a small number of specific mutations.
Counterpoint: a corruption has only a small probability of becoming fixed in the population; if reactivation is helpful, that still only has a small probability of becoming fixed, but it’s a much higher small probability.
Counter-counterpoint: no particular corruption would need to be fixed in the whole population. If there are several corruptions at independent 10% penetration each, a reactivating mutation will have a hard time becoming fixed.
The only definitively nonfunctional DNA is that which has been deleted. “Nonfunctional DNA” is temporarily inactive legacy code which may at any time be restored to an active role.
In the context “how complicated is a human brain?”, DNA which is currently inactive does not count towards the answer.
That said (by which I mean “what follows doesn’t seem relevant now that I’ve realised the above, but I already wrote it”),
Is inactive DNA more likely to be restored to an active role than to get deleted? I’m not sure it makes sense to consider it functional just because it might start doing something again. When you delete a file from your hard disk, it could theoretically be restored until the disk space is actually repurposed; but if you actually wanted the file around, you just wouldn’t have deleted it. That’s not a great analogy, but...
My gut says that any large section of inactive DNA is more likely to become corrupted than to become reactivated. A corruption is pretty much any mutation in that section, whereas I imagine reactivating it would require one of a small number of specific mutations.
Counterpoint: a corruption has only a small probability of becoming fixed in the population; if reactivation is helpful, that still only has a small probability of becoming fixed, but it’s a much higher small probability.
Counter-counterpoint: no particular corruption would need to be fixed in the whole population. If there are several corruptions at independent 10% penetration each, a reactivating mutation will have a hard time becoming fixed.
Here’s the concept I wanted: evolutionary capacitance.