If there is a gene for “needing less sleep, high behavioural drive, etc”, which seems like it ought to give an evolutionary advantage, and yet only a very small fraction of the population have the gene, there must be a reason for this.
I can think of the following possibilities:
It is a recent mutation.
The selective advantage of needing less sleep is not as great as it seems. (e.g. before artificial lighting was widespread, you couldn’t get much done with your extra hours of wakefulness)
The gene also has some kind of selective disadvantage. (If we are lucky, the disadvantage will be something like “increased nutritional requirements” which is not a big problem in the present day.)
The gene also has some kind of selective disadvantage. (If we are lucky, the disadvantage will be something like “increased nutritional requirements” which is not a big problem in the present day.)
From looking at Wikipedia’s description of orexin it does brown fat activation which is essentially burning calories for nothing but warmth.
One of the drugs which is orexin agonist that is currently in clinical trials was earlier used as a weightloss drug.
It looks like “increased nutritional requirements” is part of the selective disadvantage.
I think a version of the second and third possibilities is probably true.
For DEC2 and GRM1, the mutation decreases the ability of the gene to block wakefulness (DEC2) or promote tiredness (GRM1), and loss-of-function mutations seem easier to create. And indeed, I think one of the papers mentioned that there are other mutations in the DEC2 gene that correlate with reduced sleep, and GRM1 already has two identified short-sleeper mutations. Therefore, I expect that similar mutations have appeared in the past, but didn’t catch on.
Why would evolution have rejected them? I suspect that, as you say, 10,000+ years ago (perhaps even 1000 years ago), being awake an extra two hours before dawn brought little benefit and basically just meant that you wasted calories; the tradeoff only became worthwhile very recently, in evolutionary terms. Perhaps there were also effects like “people had a higher parasite load, and/or were constantly scraping their skin or stepping on sharp objects, and thus had a higher constant need for some type of repair that the mutations don’t accelerate”.
If there is a gene for “needing less sleep, high behavioural drive, etc”, which seems like it ought to give an evolutionary advantage, and yet only a very small fraction of the population have the gene, there must be a reason for this.
I can think of the following possibilities:
It is a recent mutation.
The selective advantage of needing less sleep is not as great as it seems. (e.g. before artificial lighting was widespread, you couldn’t get much done with your extra hours of wakefulness)
The gene also has some kind of selective disadvantage. (If we are lucky, the disadvantage will be something like “increased nutritional requirements” which is not a big problem in the present day.)
Do you have any idea which of these is the case?
From looking at Wikipedia’s description of orexin it does brown fat activation which is essentially burning calories for nothing but warmth.
One of the drugs which is orexin agonist that is currently in clinical trials was earlier used as a weightloss drug.
It looks like “increased nutritional requirements” is part of the selective disadvantage.
I think a version of the second and third possibilities is probably true.
For DEC2 and GRM1, the mutation decreases the ability of the gene to block wakefulness (DEC2) or promote tiredness (GRM1), and loss-of-function mutations seem easier to create. And indeed, I think one of the papers mentioned that there are other mutations in the DEC2 gene that correlate with reduced sleep, and GRM1 already has two identified short-sleeper mutations. Therefore, I expect that similar mutations have appeared in the past, but didn’t catch on.
Why would evolution have rejected them? I suspect that, as you say, 10,000+ years ago (perhaps even 1000 years ago), being awake an extra two hours before dawn brought little benefit and basically just meant that you wasted calories; the tradeoff only became worthwhile very recently, in evolutionary terms. Perhaps there were also effects like “people had a higher parasite load, and/or were constantly scraping their skin or stepping on sharp objects, and thus had a higher constant need for some type of repair that the mutations don’t accelerate”.