Variable mutation rates- age of puberty

I’ve already talked about how high paternal age can  increase the per-year and per-generation rates.  There’s another factor that can cause  variation in the mutation rate: differences in the age of male puberty.  At least that seems likely, from what we know of the mechanism driving the male mutation rate –  the 23 replications per year of the sperm-forming cells.

Setting up the spermatogonial cells  requires about 30 replications: after puberty, those stem cells continue dividing indefinitely, and mutations accumulate at the rate of about 2 per year.   So, all else equal, late male puberty should mean a lower male mutation rate.  In modern industrialized (i.e. chubby) populations, puberty hits at age 13.  Among Bushmen, it’s 17.

Mothers contribute about 15 mutations, independent of age, while fathers contribute about 25 +2*(g-20) – measured in Iceland, a modern industrial population.  For a modern industrial population with an average paternal age of 28 and an average maternal age of  28, generation length is 28 and the average kids inherits 56 mutations.  That’s 56 per generation, 2 per calendar year.  You’d expect to see fewer in a similar population with later puberty:  8 fewer in a population with puberty four years later.  So you’d see an average of 48 mutations per generation (85% of the previous rate) and 1.7 per calendar year.  To me this suggests that measurements of mutation rates in modern populations may not be quite the thing you want to in order estimate the long-term mutation rate in humans.  Measurement on on some fairly hard-scrabble population might be better.


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24 Responses to Variable mutation rates- age of puberty

  1. So, to reduce mutation load we need to delay puberty (calorie restriction) have early marriage, early completion of family formation, keep elderly men (over 40) and elderly women (over 30) out of the procreation cycle? Whereas as modernity gives us early puberty, late entry into childbearing, and late exit from childbearing with elderly men and some elderly women making a major contribution to mutation load?

    • minoritymagnet says:

      When we get GATTACA it won’t matter anymore.

    • rightsaidfred says:

      The problem with GATTACA is that our elites are too anxious to breed flaws into the populace. Their ideal at the moment is a deaf transgendered who will try any sexual practice.

      Wasn’t the point of GATTACA that the outsiders were better than those in the system?

    • gcochran9 says:

      Other than chromosomal errors, the number of mutations contributed by the mother seems to be nearly independent of age. Those chromosomal errors are usually so serious that their carriers have very low or zero fitness and thus don’t add to the long-term genetic load. So older mothers don’t cause long-term harm, as far as I know.

      But it’s certainly the case that most reproductive trends in the modern world have bad long-term consequences, in terms of increased mutational load and undesirable selective pressures.

      • Sorry, I was not trolling with my comment. Just a random rant. I think, the GATTACA movie has some obvious flaws anyway.

        Yes, most spontaneous aborts have chromosomal aberrations afaik. Do you think this is caused by intra-genomic concurrence among selfish genes/alleles, which do not want to end up in a polar body? Like t-allele in mice, but since not every gene has the capability to shift its probability (of ending up in the oocyte) there might be a selective pressure for most of the genome to dampen or to even prevent t-allele-like behaviour of genes.

        off topic:

        Mitochondria are one of the few exceptions to the universal genetic code (which is “designed” to make most mutations silent). My natural understanding during my studies was the following:

        There was a selective pressure on the mitochondrial t-RNA and ribosomal genes to change their genetic code, because complete horizontal gene transfer to the nucleus would render them obselete and dispensable. Thus, in the process of increasing horizontal gene transfer to the nucleus the changing mitchondrial genetic code prevented the mitochondrial genes from transferring into the nucleus and forced the eukaryotic host cell to keep and even assist the mitochondrial genome. (Nuclear genes are involved in mitochondrial protein synthesis and replication!)

        This, of course, bears the implication, that most of the horizontal gene transfer of mitochondrial (and plastid) genes occured early after establishment of endosymbiosis. That might even be testable if there are differing mutation rates in nuclear and mitochondrial DNA, which allows to estimate the relative times of horizontal transfer. In addition, the cross-species comparison of transferred and non-transferred genes might be useful.

        What do you think of this? I recently did a search to see if others shared my view, to no avail.

  2. reiner Tor says:

    GATTACA was made by the elites. So this means that the elites want us to think that we outsiders will be better than those in the system. In fact, they want us to think that any outsiders anywhere, most especially third world immigrants are better than those dumb white people in the first world.

    Like Jared Diamond writing in Guns, Germs and Steel how his very intelligent New-Guinean friends were more intelligent than your average Westerner.

    • Yes, the phenomenon has been described as being a “clever silly”: a person who makes a foolish, self denying self-criticism just to show how altruistic and kind-hearted they are. Attracts the girls, apparently. Some girls anyway.

  3. Tumescence says:

    Isn’t the very late age of puberty among bushmen an extreme case due to them living out in desert? Surely our prehistoric ancestors would’ve lived in greener habitats, been better nourished and would’ve come to puberty a bit earlier than 17.

    • Greying Wanderer says:

      The average age at which the onset of puberty occurs has dropped significantly since the 1840s.[67][68][69] This was dubbed ‘the secular trend’ by J.M. Tanner. In every decade from 1840 to 1950 there was a drop of four months in the average age of menarche among Western European females. In Norway, girls born in 1840 had their menarche at an average age of 17 years. In France, the average in 1840 was 15.3 years. In England, the average in 1840 was 16.5 years. In Japan the decline happened later and was then more rapid: from 1945 to 1975 in Japan there was a drop of 11 months per decade.

  4. Difference Maker says:

    I hit puberty at 11 and a half. Luckily, I still got a higher than average IQ. Just made to be high testosterone

  5. bruce says:

    I thought puberty for girls came at 100 pounds, with wildly spiky random variations, not to mention race stuff. Really, 4 months every 10 years? In 1350 BC did you need to wait till your wenches returned undead a century later?

    • Greying Wanderer says:

      If part of the cause was restricting reproduction until an age when even the late developers were ready and having strict sanctions on early developers that did reproduce e.g. packed off to nunneries, then it might have gone up since 1350 and then started to drop again from 1840.

    • ziel says:

      Presumably there’s a Y-intercept sometime around the dawn of the industrial revolution.

    • bruce says:

      >early developers packed off to nunneries

      Sending the party girls to the nunnery gets you a party-hearty nunnery. I don’t think it was routine enough to affect a whole society. The Victorian (or much earlier) habit of treating every lady who fell as a whore, sure. Whores die a lot.

      Healthy babies much less than five pounds are rare. Pregnancy is hard labor enough when the mother has twenty times the weight of her issue. Canoe-paddle-looking girls may hold off puberty, but most girls have enough Peggy Bundy in them to prefer a soft couch, Oprah, and chocolate. West Indies cheap sugar as the y-axis? Housework was anaerobic exercise until the 1930s or so.

      • Greying Wanderer says:

        “Sending the party girls to the nunnery gets you a party-hearty nunnery. I don’t think it was routine enough to affect a whole society. The Victorian (or much earlier) habit of treating every lady who fell as a whore, sure. Whores die a lot.”

        Yes, the nunnery thing was mainly an example of sanctions against early developers that negated any early-starter advantage. As you say for the lower classes just being pushed onto the street would be sanction enough. The main thing is sanctions for early developers would push the average age of puberty spectrum to the right over time.

  6. Greying Wanderer says:

    Purely in terms of reducing mutational load this would seem to suggest two strategies.

    1) Live fast / die young with early puberty and early childbirth.
    2) Later marriage and childbirth *requiring* later puberty (and/or various compensating cultural reinforcement).

    If you also assume two cultural options related to local food-getting requirements, “dad” or “cad” , then you get four combinations.

    Option 1 fits naturally with a cad culture but can also work in a a dad culture where early marriages are arranged and enforced.

    Option 2 would require an *enforced* dad culture to work properly imo. I think Option 2 combined with either a cad culture or an unenforced dad culture would gradually devolve to Option 1.

    The reason for this is even if there were no environmental factors like obesity lowering the age of puberty but the age was along a spectrum then all things being equal early developers would have a potential advantage over later developers as the earlier developers would have faster generations and gradually become a larger percentage of the total population.

    It seems to me this would happen unless there was no advantage to being an early developer. That could be enforced two ways:

    1) environmentally i.e. a harsh environment where the advantage of early sexual development is balanced by not being able to hunt adequately yet.
    2) culturally i.e. strict sexual / marriage morality preventing all reproduction until an age when even the late developers are ready.

    It seems to me a late puberty population would need to have one or the other to prevent the early developers displacing the late developers.

  7. Greying Wanderer says:

    To me this suggests that measurements of mutation rates in modern populations may not be quite the thing you want to in order estimate the long-term mutation rate in humans. Measurement on on some fairly hard-scrabble population might be better.

    This certainly seems the case in the underclass where the dads (who soak up whatever employment there is) and the cads seem to have (anecdotal) two distinct generation lengths.

    This made me wonder about something else. (The number will be wrong it’s just to illustrate the idea.)

    Say for the sake of argument there were two generation lengths:

    1) southern latitude cad or dad options, both at 16 years
    2) northern latitude dad option (cad option not viable until modern times) at 24 years

    assuming puberty at 13 and 2 mutations per year from age of puberty to age of reproduction gives

    1) 6 mutations (3 years times 2)
    2) 22 mutations (11 years times 2)

    but 1) has 3 generations per 48 years while 2) has 2 generations per 48 years so over 48 years it’s

    1) 18 total mutations
    2) 44 total mutations

    but if 2) can push the age of puberty up to 18 then each generation becomes

    1) 6 mutations (3 years times 2)
    2) 12 mutations (6 years times 2)

    and over 48 years (3 generations vs 2 generations) it becomes

    1) 18 mutations
    2) 24 mutations

    Like i say the numbers are just made up but if different patterns produce a different total number of generations then that seems to suggest the possibility of either

    a) a mathematically optimal age of reproduction vs age of puberty combo that minimizes mutational load

    or at least

    b) in an environment where late reproduction is neccessary for food-getting reasons (e.g. an environment where it takes longer to learn to hunt effectively enough to feed a family) then later puberty might compensate for older parenthood

  8. norkuat says:

    So I did some quick calculations on Mathematica using your scheme.
    Using Prof. Cochran formula with correction for puberty age we have:
    L[p_, f_] := [25 + 2*(f – 20) – (p – 13)*2 + 15 ]/f
    (I use [ ,] so it’s easier to see)
    p:= puberty onset
    f:= average fatherhood age
    L is the mutation rate per year assuming f= years of each generation
    It’s a simple optimization problem so:
    FindMinimum[{L[x, y], 11 <= x <= 17, x <= y 17., y -> 17.}} I used 17 since this is kinda late puberty onset but can be longer (data?) Minimization will choose late puberty age
    In essence what it says is that the important thing is the gap between p and f.should be minimum (this is obvious -_-) I don’t think this is close to zero anywhere so I don’t know. So maybe the optimal response to current dysgenic trends should be using high iq post pubescent studs(they’ll surely agree xD)
    The factor two of 2*(p-13) is just an average and should be larger since mutation rate is not constant on a lifetime, in fact is slower near puberty(that’s why it should be larger). If this is done the L is smaller but the pattern is the same. We NEED to add nonlinearity

    • gcochran9 says:

      It is not just an average: the rate is in fact close to linear in measurements thus far. We could stand to have more information about the rate in the 50s and 60s though.

  9. Greying Wanderer says:

    I’m not sure my previous example was very clear so i’ll try again as i find this very intriguing.

    Say reproduction in the past tended to occur on average four years after puberty and you have two populations:
    A) puberty at 13, reproduction at 17
    B) puberty at 17, reproduction at 21

    Then both populations have the same gap of four years for mutations to occur within each *single* generation but population (A) has 1.24 more generations than population (B) over n years so (B) has a lower total mutational load over *multiple* generations. If i have the sums right then i think it means that with an average age of puberty at 17 then opulation (B) will have either a lower or equal total mutation load to (A) up to an average reproductive age of 25.

    If so then the traditional late marriage euro model might have been very beneficial *while* puberty was kept late becoming bad only when the high average age of puberty started to decline from the 1840s (caused somehow or other by industrialization?)

    • Greying Wanderer says:

      “If i have the sums right then…up to an average reproductive age of 25”

      Which i don’t and that bit is wrong but never mind as it doesn’t effect the main idea. If the gap in years between puberty and reproduction is the same and the rate of mutation is the same (at least at these ages) then later puberty / reproduction will generate lower levels of load over time due to the smaller number of total generations over time.

  10. Greying Wanderer says:

    Another thought. There was a post here some time ago about mutation rates varying by temperature i.e. climate. That may factor into this as well. If northern latitudes had a lower rate of mutation then an average age of puberty of 17 combined with average age of first reproduction marriage at say 24-ish i.e. a gap of 7 years might have been the same as a gap of 4 years in the tropics?

    And another slightly separate but related to the idea that there might only be a tiny handful of stable reproductive patterns available depending on the environment. If repeated close-cousin marriage creates lots of inbreeding problems it seems to me this could be compensated for with a marriage culture that combined very high fertility and very high mortality. Say for the sake of argument long-term close cousin marriage led to 1 healthy kid out of 5 then having very high fertility would lead to lots of throws of the dice so out of ten kids you get two healthy ones leaving the very high mortality to deal with the sickly ones. The end result might be a healthy population as long as both conditions are maintained.

    If either or both of the conditions change to low fertility or low mortality then the negative effects of repeated close-cousin marriage could pile up very quick?

    Similar to how the european late marriage system might have been fine or even optimal when the average of puberty was 17 becoming less so as the age of puberty drops.

    • Greying Wanderer says:

      “a gap of 7 years might have been the same as a gap of 4 years in the tropics?”

      should have been

      “a gap of 7 years between end of puberty and reproduction in northern latitudes might generate on average the same total number of mutations as a gap of 4 years in the tropics?”

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