Chimps & humans split twice as long ago as previously thought (part 3)

Research discovers fathers are responsible for 75% of mutations in their kids, revealing that chimps & humans split twice as long ago as previously thought


Most scientists think that the human family split from the chimpanzee family around 5 – 7 million years ago. However, advances in technology are allowing us to gather a lot more genetic data a lot quicker. Whilst it took us more than a decade to sequence the genome of one human, in the subsequent decade we’ve sequenced 1,000 genomes! Armed with this bigger, better dataset researchers recalculated the chimp/human split; revealing it actually occurred 7 – 14 million years ago, more than twice as old as previously thought1.

The recalculated divergence of humans and chimps

The recalculated family tree of humans, chimps and other apes (but we don’t care about them)

And now for something completely relatively different:

Another upshot of all this new genetic data is the discovery that the age of a father influences the number of mutations in their children. Whenever cells divide there is a chance the copying process will make mistakes, leading to mutations. As such the older someone is the more mutations they’ll have in them; meaning they’re more likely to pass some on to any kids they have. This primarily affects men as they’re producing sperm throughout their lives (so it’s continuously dividing and accumulating mutations), whilst women aren’t continuously producing eggs.

When all is said and done this adds up to roughly 2 extra mutations in the kid for every year of the fathers’ age; meaning that men are “responsible” for about 75% of the mutations in their kids2.

And now to masterfully bring these two threads back together:

Many scientists objected to the 7 – 14 million year figure for the human/chimp split because of this research into the father’s age and mutations. The new date for the split was calculated by looking at the number of mutations that accumulate per generation (then working out how many generations would have to have passed to result in the number of mutations that separate us from chimps), but this age-mutation research indicates that this could be a highly variable figure, depending on the age of the parents3.

The researchers behind the 7 – 14 million year old figure (hereafter called the “old” figure because I’m too lazy to keep typing all that out) defended their conclusion, saying that whilst age could influence mutations per generation; it did not change drastically enough to render their findings invalid. Nonetheless, they admitted that more research should really be done into the subject to make sure they weren’t barking up the wrong (family) tree4.

At the very least more research could help refine the old figure. 7 – 14 million years is a lot of time, finding a more specific age for the split would be good.

And just last week “more research” on the subject was published! A team of researchers from England and the Netherlands examined the genomes of three generations of a chimpanzee family in exquisite detail; studying the relationship between the age of fathers and mutations in their offspring, as well as whether this influences the estimated date of human/chimp divergence. This investigation had some rather interesting conclusions2:

  • Some parts of the genome may be more ‘susceptible’ to change, with 20% of mutations occurring close to another.
  • Whilst the father’s age results in 2 mutations per year in humans, it’s 3 mutations per year in chimps. This is quite a significant difference (a 50% change) despite the fact we’re so closely related
  • The extra age mutations in chimps means the father is responsible for 90% of the mutations in kids, compared to 75% in humans.

But the most important conclusion of all (to me at least) is that they were able to still calculate when humans and chimps diverged, taking into account the effect of father’s age. Their figure is a split 13 million years ago; consistent with the earlier old figures that have previously been criticised.

This is yet more evidence that our family is a lot older than we once thought. Also some interesting stuff about mutations, but I don’t know enough about genetics to be really blown away by that.

 References

  1. Langergraber KE, Prüfer K, Rowney C, Boesch C, Crockford C, Fawcett K, Inoue E, Inoue-Muruyama M, Mitani JC, Muller MN, Robbins MM, Schubert G, Stoinski TS, Viola B, Watts D, Wittig RM, Wrangham RW, Zuberbühler K, Pääbo S, & Vigilant L (2012). Generation times in wild chimpanzees and gorillas suggest earlier divergence times in great ape and human evolution. Proceedings of the National Academy of Sciences of the United States of America, 109 (39), 15716-21 PMID: 22891323
  2. Oliver VennIsaac Turner, Iain MathiesonNatasja de Groot, Ronald Bontrop, Gil McVean. 2014. Strong male bias drives germline mutation in chimpanzees. Science, 344(6189):1272-1275
  3. Gibb, G. C., & Hills, S. F. (2013). Intergenerational mutation rate does not equal long-term evolutionary substitution rate. Proceedings of the National Academy of Sciences110(8), E611-E611.
  4. Prüfer, K., Langergraber, K. E., Pääbo, S., & Vigilant, L. (2013). Reply to Gibb and Hills: Divergence times, generation lengths and mutation rates in great apes and humans. Proceedings of the National Academy of Sciences110(8), E612-E612.

Related Articles

21 thoughts on “Chimps & humans split twice as long ago as previously thought (part 3)”

  1. Clubfoot says:

    Jebus! We split from chimps 13 million years ago now! This means there must be a whole load more fossils recording our evolution from the common ancestor to be found.

    1. Adam Benton says:

      I’m not hugely familiar with the fossils from this period; but there are a few interesting ones that might have to be re-evaluated in light of this discovery. However, finding more fossils might be rather difficult, as it seems we were living in jungles during this period; which do not preserve fossils particularly well (which is why we have so few chimp fossils)

  2. Cynthia Echterling says:

    Did they take into account average life expectancy and breeding frequency for those geriatric ancient males? During what age range do male chimps do most of their successful breeding?

    1. Adam Benton says:

      They used their data on these 9 chimps to elucidate on these issues; although thinking about it that does seem like a rather small sample size.

      I guess yet more research is needed to vindicate this claim

  3. Jim Birch says:

    This news should make the creationists feel marginally better we are still great apes but arguably a bit less. 🙂

    1. NovaSaber says:

      But chimpanzees are still more closely related to us than they are to gorillas, and both chimpanzees and gorillas are more related to us than to orangutans. Those facts, not how recent our common ancestor was, are the reason for classifying humans within the great apes.

  4. eyeonicr says:

    What kind of assumptions do they have to make about when 10 million year old apes were having their children, and what do we actually know about that? Presumably they were doing so earlier than we do today, but there must surely be a fair bit of uncertainty.

    1. Adam Benton says:

      There is a fair bit, their age range for the split was 11 – 17 mya, which is a fairly large margin of error

  5. cynicalme says:

    So how far back does this push out our divergence with Neanderthals then? 600,000 – 1 million years? Wouldn’t this also affect our estimate for when mitochondrial eve lived?

    1. Adam Benton says:

      Since we’re mostly dealing with the male line this probably doesn’t impact the the estimates for mtEve; although it may well alter our estimates for Y-chromosomal Adam. As for the Neanderthals, they didn’t specifically deal with it in this study but in the others I’ve discussed before this new data put the split at 400 – 800,000 years ago.

  6. James R Lumbard says:

    The biggest blow to their argument is where they admit they are “assuming uniformity of the mutation rate over this time”.
    However, I’m quite taken by Eldgredge & Gould’s theory of evolution through punctuated equilibrium where the background rate of mutation is greatly accelerated during times of change, for example environmental change forcing adaptation to a new climate or modified habitat, with mutation rates falling back to the steady state once adaptation has occurred and pressure to evolve is relieved.
    Such a mechanism for evolution will naturally over-estimate divergence dates if a constant rate of mutation is assumed.
    Thoughts?

    – James

    1. eyeonicr says:

      Does punctuated equlibrium involve a change in the mutation rate, or just the rate of adaptation? The evidence for a broadly constant mutation rate seems pretty solid.

      1. Adam Benton says:

        Yeah, it seems to be an increase in selection pressures rather than mutations

    2. Adam Benton says:

      I was under the impression that punctuated equilibrium represented an increased strength in selection pressures driving evolution forwards; rather than any change in mutation rate.

      1. James R Lumbard says:

        Point conceded, given that molecular clocks are based on mutation rates in regions of genes that, necessarily, are highly conserved due to basic life-supporting functions.
        As an aside, some fairly recent findings in snakes are particularly interesting in this respect: http://www.newscientist.com/article/dn24684-snakes-outpacing-other-vertebrates-in-race-to-evolve.html#.U6SGNSi9aGM
        and particularly this PLOS article (love a good open access journal, me) http://dx.plos.org/10.1371/journal.pone.0002201

        – James

        1. Adam Benton says:

          That was going to be my second point, but I wanted to focus on mutations and punctuated equilibrium. If I have a misunderstanding of a basic aspect of evolutionary theory I’d like to know. It’s kinda important.

          In other news, would you ever be interested in writing a guest post for EvoAnth?

        2. James R Lumbard says:

          An increased strength in selection can indeed cause a punctuation event. I’m sure you know that for evolution to occur in response to selective pressure, a mutation must occur (or have occurred) to create a new allele, which must then reach fixation in a given population. Given that fixation is reached more quickly in a smaller population and causes genetic drift (the founder efffect), more mutations occur and reach fixation in a given period of time. In a larger population, these mutations would be diluted to homeopathic levels, are very unlikely to reach fixation and would have very have cumulative effect evolutionarily.
          This dilution amounts to neutral evolution where genetic changes continue to occur, while function/phenotype simply fluctuates around the mean. This dynamic stasis could either be maintained by the effect of stabilising selection in the face of ecological constraint or is simply not permitted because genetic diversity is too low.
          My (hastily refreshed) opinion is that the rate of fixation (or ‘permanent mutation’, if you will) is accelerated in punctuated equilibrium, and I agree that this does not require any increase in the baseline rate at which mistakes are actually introduced during DNA replication.

          (Stop me if I haven’t actually answered your question).

          In other news, yes, I would be very interested in providing a guest post at some point – I’m flattered.

  7. Pingback: Tomkins’ 70% | Eye on the ICR
  8. Trackback: Tomkins’ 70% | Eye on the ICR
  9. Bob GutSmasha says:

    I’m still just trying to wrap my head around these time scales; the timespan for evolution is so enormous.

    I realize this is a bit abstract but what would 100,000 years in evolution compare to in a human lifetime? A day, a week, month, or year? I’m reading Dawkin’s “Evidence for Evolution” and he tries to capture the scale in various ways, but I feel my brain melt.

    1. eyeonicr says:

      4 billion years is to 100,000 years as 100 years is to about 22 hours, if that helps.

      1. Bob GutSmasha says:

        Yeah that does help a little, thanks.

Leave your filthy monkey comments here.

More in Evolution of our body
Human ancestors caught Herpes off chimps 1.6 million years ago

Humans have one more version of the Herpes virus than any other primate. New research reveals this is because one...

Close