Using 16 ATP instead of 8, and 80/6=13.33 years, won’t change the result significantly. It seems off by many orders of magnitude (to claim natural selection based on energy expenditure).
1% of diet is a selectable-sized difference, certainly. But the selection pressure applies to individual base pair mutations, which are conserved or lost independently of one another (ignoring locality effects etc). The total genome size, or total “junk” size, can’t generate selection pressure unless different humans have significantly different genome size. But it looks like that’s not the case.
But the selection pressure applies to individual base pair mutations
I am confused why you believe this. Evolution need not splice out bases one base at a time. You can easily have replication errors that could splice out tens of thousands of bases at a time.
No, replication is more robust than that. I have never heard of large insertion or deletion in replication, except in highly repetitive regions (and there only dozens of bases, I think).
However, meiotic crossover is sloppy, providing the necessary variation.
Speaking of meiotic crossover, non-coding DNA provides space between coding regions, reducing the likelihood of crossover breaking them.
...I seem to have assumed the number of BP changed by small or point mutations would make up the majority of all BP changed by mutations. (I was probably primed because you started out by talking about the energy cost per BP.) Now that you’ve pointed that out, I have no good reason for that belief. I should look for quantified sources of information.
OK, so now we need to know 1) what metabolic energy order of magnitude is big enough for selection to work, and 2) the distribution of mutation sizes. I don’t feel like looking for this info right now, maybe later. It does seem plausible that for the right values of these two variables, the metabolic costs would be big enough for selection to act against random nonfunctional mutations.
But apparently there is a large amount of nonfunctional DNA, and also I’ve read that some nonfunctional mutations are fixated by drift (i.e. selection is zero on net). That’s some evidence for my guess that some (many?) nonfunctional mutations, maybe only small ones, are too small for selection pressure due to metabolic costs to have much effect.
Yeah, I will definitely concede small ones have negligible costs. And I’m not sure the answer to 1) is known, and I doubt 2) is well quantified. A good rule of thumb for 2) though is that “if you’re asking whether or not it’s possible, it probably is”. At least that’s the rule of thumb I’ve developed from asking questions in classes.
Using 16 ATP instead of 8, and 80/6=13.33 years, won’t change the result significantly. It seems off by many orders of magnitude (to claim natural selection based on energy expenditure).
1% of diet is a selectable-sized difference, certainly. But the selection pressure applies to individual base pair mutations, which are conserved or lost independently of one another (ignoring locality effects etc). The total genome size, or total “junk” size, can’t generate selection pressure unless different humans have significantly different genome size. But it looks like that’s not the case.
I am confused why you believe this. Evolution need not splice out bases one base at a time. You can easily have replication errors that could splice out tens of thousands of bases at a time.
No, replication is more robust than that. I have never heard of large insertion or deletion in replication, except in highly repetitive regions (and there only dozens of bases, I think).
However, meiotic crossover is sloppy, providing the necessary variation.
Speaking of meiotic crossover, non-coding DNA provides space between coding regions, reducing the likelihood of crossover breaking them.
Meiotic crossover is what I meant, actually. Generally the polymerase itself wouldn’t skip unless the region is highly repetitive, you’re right.
...I seem to have assumed the number of BP changed by small or point mutations would make up the majority of all BP changed by mutations. (I was probably primed because you started out by talking about the energy cost per BP.) Now that you’ve pointed that out, I have no good reason for that belief. I should look for quantified sources of information.
OK, so now we need to know 1) what metabolic energy order of magnitude is big enough for selection to work, and 2) the distribution of mutation sizes. I don’t feel like looking for this info right now, maybe later. It does seem plausible that for the right values of these two variables, the metabolic costs would be big enough for selection to act against random nonfunctional mutations.
But apparently there is a large amount of nonfunctional DNA, and also I’ve read that some nonfunctional mutations are fixated by drift (i.e. selection is zero on net). That’s some evidence for my guess that some (many?) nonfunctional mutations, maybe only small ones, are too small for selection pressure due to metabolic costs to have much effect.
Yeah, I will definitely concede small ones have negligible costs. And I’m not sure the answer to 1) is known, and I doubt 2) is well quantified. A good rule of thumb for 2) though is that “if you’re asking whether or not it’s possible, it probably is”. At least that’s the rule of thumb I’ve developed from asking questions in classes.