Blame Your Subpar Fitness on That Neanderthal DNA

By Bridget Alex | July 13, 2016 11:26 am
Neanderthal-in-museum

A Neaderthal strikes a pose at the State Museum of Prehistory in Halle, Germany. (Credit: Bridget Alex)

Most of us harbor about 2 percent Neanderthal DNA, inherited when our ancestors bred with Neanderthals more than 50,000 years ago. This was revealed back in 2010, when geneticists salvaged enough fragments of ancient DNA from Neanderthal bones to piece together a full genome. The discovery squelched a longstanding debate over whether Neanderthals and modern humans met — they did — and mated — oh yeah.

But why do we only have 2 percent Neanderthal ancestry? And what are the effects of that Neanderthal DNA on living humans? And why did our ancestors survive and Neanderthals go extinct? We’ve attributed our supremacy to bigger brains, better diets and advanced technology, but there may be a subtler, less flattering explanation for our evolutionary success.

Strength in Numbers

Computational geneticists Kelley Harris of Stanford University and Rasmus Nielsen of the University of California, Berkeley propose a simple answer to all of these questions: Due to their smaller population size, Neanderthals were less evolutionary fit than modern humans, for the same reason that small, inbred groups today are less healthy. In small populations, mildly harmful mutations are more likely to persist and rise in frequency, while in larger populations they are weeded out by natural selection.

In a recent study published in Genetics, Harris and Nielsen use computer simulations to show that the average Neanderthal would have had at least 40 percent lower evolutionary fitness than the average modern human at the time they met. This means Neanderthals would have had fewer surviving offspring than modern humans when the groups were in the same place, at the same time — fewer offspring = lower evolutionary fitness.

The hybrid offspring of Neanderthal-modern human lovers would also have been less fit, and those small bits of Neanderthal DNA in present-day humans may reduce our fitness by 0.5 percent.

Goodbye, Hello, Goodbye Again

Neanderthals and modern humans split from common ancestors in Africa over 500,000 years ago. The ancestors of Neanderthals migrated to Eurasia and evolved into the classic Neanderthal form, while our ancestors remained in Africa and evolved into modern humans. The groups were then separated for hundreds of thousands of years — plenty of time to evolve distinct morphologies, behaviors and cultures.

neanderthal-dig

Archaeologists try to understand the differences between Neanderthals and modern humans by comparing their fossils and artifacts. Here archaeologists dig in Manot Cave, Israel, where modern humans likely stopped as they spread from Africa to Europe roughly 50,000 years ago. (Credit: Bridget Alex)

Sometime after 100,000 years ago, the groups reunited when modern humans migrated out of Africa and encountered Neanderthals in Eurasia. Within 60,000 years, the distinct Neanderthal form disappeared, with the Neanderthal lineage only surviving as 1.5 to 2.1 percent of the genomes of living humans. The only groups today that seem to be Neanderthal-free are recent hunter-gatherer groups in Africa like the Yoruba and San, whose ancestors probably never encountered Neanderthals.

A Good Fit

What makes the model of Harris and Nielsen so compelling is that it fits what we know from ancient and modern genomes. First, based on measures of genetic diversity, the population of Neanderthals was probably 1/10th the size of modern humans at the time of contact.

Neanderthal genetic diversity was lower than any living human group, including isolated groups like the Fuegians or Druze. In fact, it was among the lowest measured for any organism.

Next, the claim that Neanderthals were less fit is supported by the observation that Neanderthals had more mutations that change amino acids, the building blocks of proteins.

Finally, there is evidence that Neanderthal DNA has been mostly detrimental to modern humans and selected out of our genes. Although several Neanderthal mutations may have been beneficial — changes relating to hair, pigmentation and immunity — overall Neanderthal DNA is rare in our protein-coding genes

The blame-it-on-population size idea is theoretically and empirically supported, but rather anticlimactic for the narrative of modern humans. Our ancestors may have outcompeted Neanderthals, not through intellect or innovation, but through demographics — the mundane fact that we came from a larger, fitter stock.

 

Bridget Alex holds a PhD in Anthropology and Human Evolutionary Biology, and her research is focused on understanding how modern humans dispersed globally, as Neanderthals and other human types went extinct. She is a AAAS Mass Media Fellow, writing for Discover this summer.

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  • http://www.mazepath.com/uncleal/qz4.htm Uncle Al

    Don’t breed with anything bearing a low serial number. So has it ever been. (Is that you, Dave Attell?)

    • j2saret

      Or bred on Monday or Friday?

  • Jenny H

    Wots rong wiff us Neanderthalians?

    • Borsk Fey’lya

      Not a great deal of controversy when one of the subject groups cannot speak for themselves, huh?!

  • Sahin CAKIR

    ALTERNATIVE: Blame the retrogressive dominance in DNA

    See Section 12 in” Birth of modern human neither in Africa nor gradual, but macroevolutionary in the Levant circa 150,000 years ago”

    • Scrub DeScrub

      Thanks! I will.

  • zlop

    Zeka regresses modern humans to Neanderthal appearance?

    • ECarpenter

      No. Their brains were larger than ours.

      • zlop

        Self domestication will turn us into science fiction aliens?

      • J Smith

        and populations of H. Sapiens with neaderthal or denisovan DNA today have on average larger brains and higher IQ than those without

  • j2saret

    The only actual other race.

    • Daiyu Hurst

      No, there were also the Denosovians. And we may yet find more species, but not likely many more. But I would still not use the word race to describe them any more than I would trees.

      • j2saret

        Not sure they were wide spred enough but I’ll give you that. So three known races of humans then, unless you are going for none or hundreds based on minute variations in skin, hair, eye and ear wax colour.

      • ECarpenter

        “Race” once upon a time meant kin-group or extended kin group. It was a perfectly good English word which then got permanently damaged by the whole 17th / 18th century redefinition of race into huge imaginary classes of people. So sad.

    • Rahsaan Chisolm

      Thank you! Human geographical phenotypes are akin to breeds in dogs. We’re all the same race/species.

      • goldlions

        Not according to the Neanderthal Y.

        • Rahsaan Chisolm

          goldlions, I was referring to everyone within the Sapiens grouping. Yes. Neanderthal is a separate race. All sapiens are the same race despite how we incorrectly use the term.

    • Joel F

      There are no “races” because that is a social construct. We are one species, with no subspecies. We could argue that maybe Neanderthal was a different species but could still mate with H. Sapiens successfully.

      • j2saret

        No you couldn’t because the offspring were fertile. Race, a social constuct, as is every other concept encoded in a language applies perfectly here.

  • Lorie Franceschi

    For same reason that our cousins died out (small population and in breeding) is the problems that European royalty had and have some major health problems. Almost all of them are descendants of William the first or William the Conqueror and back farther to Charlemagne

  • John Do’h

    Seems to be a subject that is not want to brought up… but it would be unlikely that the Modernhuman X Neanderhuman interaction was friendly. Modernhumans were probably even less civilized than ISIS, killing the Neaderhuman males and raping and enslaving the women/children.

    • Scrub DeScrub

      (Hands over ears)
      *LA LA LA LA*
      I can’t hear you! I can’t hear you!

      *sobbing*

  • stargene

    Working out the story between Neanderthals and H. sap has only just begun. Did they accumulate a higher % of detrimental genes? Yes.
    But we already knew they lived in far smaller enclaves, which were
    probably more widely separated, than the newcomers. They had far
    harder lives, with significantly greater mortality, since ‘wrestling’ with
    and overcoming great megafauna was more important in their diets
    than ours. And to replace their losses, they actually matured earlier.
    But this ‘think piece’ implies that we’d have been better off if we’d
    never met the big red-haired dudes. Sloppy thinking. We all leapt
    to conclusions 100 years ago about how stupid H. neanderthalensis
    was, compared to our wonderfulness. Let’s not make the same
    stupid mistake again.

  • Neal Stevens

    But why were the Neanderthals, as opposed to ancient human ancestors, such a small, genetically non-diverse population to begin with? Surely, we were all derived from the same parent organism. So why did the human strain go on to become genetically diverse and large in population size while the Neanderthal strain, derived from the same source, become non-diverse and limited in population size?

    • okiejoe

      Perhaps they were smart enough to foresee a great population explosion with people living in mega-caves with hours long commutes to the mammoth herds and so they instituted birth control. Unfortunately for them H Sap couldn’t see that far ahead and killed off the smart ones. And we have regularly practiced genocide ever since.

      • OWilson

        There was simply no “Neanderthal Lives Matter” in those days! :)

      • J Smith

        Most species of animals practice genocide

  • Dennis Morrisseau

    Neanderthal brains were larger than ours, for one thing.
    And I have read scholars who insist that Neanderthal DNA in us varies widely…..very widely. Your numbers are just a world-wide AVERAGE
    that includes many African groups in it that have zero Neanderthal DNA.

    Some individuals and peoples have a lot more than the AVERAGE #
    you cite here.

    • Scrub DeScrub

      I have a goodly amount of Neanderthal DNA, according to testing.
      It keeps me humble.

      Well, that & my wife.
      Did I say that out loud…?

  • kmtominey44

    Gee, dominated a very harsh environment through recurring glacial periods for what, 350-400 thousand years. They certainly were not stupid or unhealthy in their genetics. H. Sapien may have out competed them but lets see if they are still around in 300 thousand years.

    • J Smith

      Exactly. And human populations with more Neanderthal or Denisovan DNA have on average 8 to 12 point higher IQ averages

  • StanChaz

    So THAT explains the embarassment of a Trump candidacy!

    • http://www.mazepath.com/uncleal/qz4.htm Uncle Al

      Trump for President! Close enough for government work.
      On the basis of coarse and abundant body hair, Hillarity Ramrod Clitler wins by a shin.

    • J Smith

      Nah it explains why lower IQ (non Neanderthal bearing populations) voted for Hillary.

  • P.Mathivanan

    Blaming Neanderthals will only make us more sub par fitness. Let’s have a healthy living.

  • ECarpenter

    “The hybrid offspring of Neanderthal-modern human lovers would also have been less fit”

    Is that really how natural selection works? And do we really have enough Neanderthal DNA to claim that they had very low genetic diversity? Couldn’t it equally be that there were just too few of the half-and-half people, too separated from each other, to get established as a separate species because their potential mates were all either full human or full Neanderthal?

    It’s obvious that Neanderthal were unable to adapt successfully to something, but as many researchers have pointed out, looking at the patterns of our ancestor’s movement into the ranges of other hominids, that something may very well have been being hunted down by our own ancestors. Yes, I guess that can be called “less fit”, but that’s misleading.

  • Brian Hanson

    The San supposedly have Eurasian genetic influence from a return to Africa 3,000 years ago of a Eurasian tribe. Shouldn’t the San therefore at least have some Denisovan genes?

  • Brian Hanson

    I understood that all modern humans from outside Africa are the descendants of about 200 humans who left Africa. Wouldn’t that mean that non-African modern humans are less evolutionary fit than African modern humans due to the lack of genetic diversity?

    • Scrub DeScrub

      I don’t know the numbers on modern Africans’ genetically-caused health issues compared to First World countries.
      Aside from starvation and infection, though, which our modern science & technology has given us the means to fight (usually quite easily and successfully) I would bet $$ that the average *healthy* Bushman is generally stronger, has more stamina, and definitely has better teeth than the average 1st world couch surfer.

    • J Smith

      No. Some populations are more fit when it comes to intellectual ability, which is more important once technology and civilization was developed by those neaderthal and Denisovian bearing humans

      • Brian Hanson

        Except we still need the rest of our genetics (other than just those related to intellectual ability) to be fit so that we may survive the effects of our technology and increased intellect. In addition, non-African populations around the world are only 2-4% Neanderthal or Denisovan, therefore non-Africans received the bulk of their genetics from the several hundred modern humans that out-migrated from Africa, while genetic Africans received 100% of modern human genetics. Human technology has also been flowing back to and from Africa.

  • nik

    Larger brains do not necessarily mean higher intelligence.
    Computers that used to need huge buildings with their own generating stations can now be outperformed many times over by a mobile phone, or a pocket calculator.
    Its connections that count.
    From tool history, its evident that Neanderthal toolmaking virtually stagnated, while HS toolmaking evolved significantly faster, into modern days highly tooled society.
    Tools enable the physically less fit to survive and prosper, where they otherwise could not.

    • Scrub DeScrub

      Larger groups also enabled people to “specialize” in what they were particularly suited to or talented in, as well.
      When only a relative few have to focus on building for all, or planting and/or reaping for all, hunting or for all, making tools for all, etc everyone in the society is healthier than when having to take care of ALL of their own survival needs, along with those of their offspring.
      There are only so many hours in a day…

      • nik

        That was demonstrated by the decimation of the African population by the slave trade, which stunted it development, compared to the rest of the world.
        It had been happening for millennia,, but when the ‘west’ got involved, it escalated to industrial scales.
        The only saving grace, was that Britain, one of the perpetrators, was also responsible for its abolition.

        • Scrub DeScrub

          Yeah, I see exactly what you mean.

          • J Smith

            Exactly. And human populations with more Neanderthal or Denisovan DNA have on average 8 to 12 point higher IQ averages.
            And that holds up in populations that were NOT subject to slave trade. if anything the slave trade increased intelligence averages as a result of the trade

          • Scrub DeplorableScrub

            Agreed.

        • Kate K

          Slavery has been around — and around worldwide — for as long as human civilization.

          Britain ended slavery on Britain only because it figured out how to even better exploit people

          • nik

            As I said;
            ”It had been happening for millennia,”
            :-)

          • Kate K

            To everyone by everyone. The idea that one population was more affected is not supported.

  • Erik Bosma

    I’ll tell you what happened to the Neanderthals… they were absorbed by us (and by us I mean them too). The Neanderthal women liked the looks of those new boys and selected then over their own boys. It’s always the females who get to direct evolution. Eventually there were no more eligible Neanderthal men left. And after the point we were all one happy family again. Either that or we ate them.

    • Erik Bosma

      I mean, “after that point…” but you caught that already.

  • The_Dude

    Everyone knows this is all make believe. This magical spaghetti monster picked up some dirt and bam your great 10 to the 3rd power grandpa was born. Then the spaghetti monster took the poop of your great 10 to the 3rd power grandpa and bam your great 10 to the 3rd power grandma was born. Now give me money.

    • J Smith

      We get anti since statements even from Discover though.
      In fact human populations with more Neanderthal or Denisovan DNA have on average 8 to 12 point higher IQ averages. more cultural and technological development, at much earlier stages as well.

  • Rick Taylor

    Did I just read that there were beneficial Neanderthal genes related to “hair, pigmentation, and immunity”?
    Did white skin come from Neanderthals?

    • Joel F

      Yes, it appears that white skin and red hair came from Neanderthal along with things like Parkinson’s disease, I think mucus filled noses, that weird bump on the back of some people’s skulls, big hands, probably blue eyes, Type 2 diabetes, lupus, biliary cirrhosis and Crohn’s disease.

    • J Smith

      Parkinson’s, Lupus, Type 2, cirrhosis occur in populations with no neaderthal as well as populations with Neanderthal.

  • J Smith

    . And human populations with more Neanderthal or Denisovan DNA have on average 8 to 12 point higher IQ averages

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