Neanderthals didn’t “evolve”

Evolution describes how animals change over time. Often this is driven by natural selection – a process which results in animals becoming better adapted for their environment. However, people often forget about natural selections little brother: genetic drift. Or to put it more simply “chance”.


Evolution describes how animals change over time. Often this is driven by natural selection – a process which results in animals becoming better adapted for their environment. However, people often forget about natural selections little brother: genetic drift. Or to put it more simply “chance”. Yes, evolution can change animals to become better adapted; but it can also change them for no real reason. New research suggests that the evolution of the Neanderthals may be the result of the latter.

Broadly speaking, genetic drift refers to how new mutations and features can spread through a population (causing it to change) even if they aren’t beneficial. Maybe the competitors of a group are wiped out by a natural disaster, allowing the group (and its odd mutations) to flourish. Maybe one group migrates into a new region. Full of untapped resources, their population explodes. Maybe due to chance, one lineage just doesn’t have as many offspring as another causing their mutations to vanish.

By chance red marbles reproduce less frequently; allowing blue marbles to rise to dominance for no real reason

By chance red marbles reproduce less frequently; allowing blue marbles to rise to dominance for no real reason

There’s been a lot of debate over whether or not natural selection (where traits spread through a population because they confer an advantage) or genetic drift is the primary driving force of evolutionary change. The result of all this argument has been a resounding: it depends. In small groups genetic drift definitely seems to take a high priority. It doesn’t take much chance (whatever that chance event might be) to tip the scales in favour of one change or another. Sometimes a single family dying could mean the extinction of a mutation; allowing others to rise to dominance simply because they dodged the meteor or whatever. On the other hand, these sorts of events would have a less significant impact on larger populations.

And that’s where the Neanderthals enter into the picture. During their evolution they were living in ice age Europe. Now, granted it wasn’t always frozen over but it was still a pretty tough place to live. As such, estimates indicate that the Neanderthal population size remained pretty low. Thus they would have been strongly influenced by genetic drift.

In fact, the dates key Neanderthal traits appear often correlate with particularly trying times where the Neanderthal populations would be extra small. At some points there appear to have been fewer than 8,000 Neanderthals on the planet.

The prominence of genetic drift in their evolution may go some way towards explaining the “quirks” of Neanderthal anatomy. For example, they had rather large noses. This had been explained as an adaptation to the cold environments (heating up the air before it entered the body). Yet when you look at living cold adapted species (including some groups of humans) the opposite trend is observed, with noses becoming smaller. Might the Neanderthal nose have developed by chance and not for any reason?

Bits of the skull that separate humans (right) from Neanderthals (left).

Bits of the skull that separate humans (right) from Neanderthals (left). Note the (unlabelled) larger nose hole

Now of course it’s  worth noting that this research doesn’t actually establish that certain Neanderthal characteristics are the result of genetic drift. Simply that they were in a position to be strongly influenced by it. In other words (as with just about anything on this subject) more work is needed. After all, if the environment was harsh enough to limit their population it was likely exerting a strong pressure on them that could’ve drive more natural selection than expected.

Us modern humans, on the other hand, lived in a slightly large population. So we likely evolved for a reason.

Reference

Pearson, O. M. (2013). Hominin Evolution in the Middle-Late Pleistocene. Current Anthropology, 54(S8), S221-S233.
Rae, T. C., Koppe, T., & Stringer, C. B. (2011). The Neanderthal face is not cold adapted. Journal of human evolution, 60(2), 234-239.

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8 thoughts on “Neanderthals didn’t “evolve””

  1. Paul Braterman says:

    They were, as you mention, relatively chinless. This puzzles me; I thought the current explanation of the human chin was as a byproduct of the geometry of jaw development; if so, why should they have been different?

    BTW, I think it’s confusing to say that genetic drift does not count as evolution. Larry Moran (I’m sure you follow his Sandwalk blog) would not be pleased.

    1. Adam Benton says:

      Well I hope the article makes it clear that they are part of the same process. I was simply trying to point out that genetic drift isn’t what most people think of when they think of evolution.

      The chin thing is just us being weird; all other hominins follow the Neanderthal pattern

      1. Paul Braterman says:

        Genetic drift?

        1. Adam Benton says:

          Perhaps; the paper notes it would also have affected us. However natural selection would have played a much more prominent role in our development. They estimated that Neanderthals were almost exclusively influenced by genetic drift

        2. Paul Braterman says:

          Belatedly, perhaps, I get it. Adaptive evolution is to drift much as signal is to noise.

        3. Adam Benton says:

          Yet both are technically evolution; even if one tends to get overlooked.

  2. Steve says:

    What if large noses were just selected for because culturally they were considered to be an attractive trait. In this case, they wouldn’t need to confer a survival advantage to be selected for and they wouldn’t necessarily need to have arisen through drift either.

    While genetic drift probably plays a large role in the evolution of DNA sequences that aren’t expressed (e.g. junk DNA), we should probably be careful when applying it to changes that affect the phenotype in obvious ways because there could be any number of non-intuitive reasons why that particular feature lead to a reproductive advantage.

  3. Dwarf Elder says:

    After Heidelbergensis (trolls) disappeared, Neanderthals/Denisovans (Dwarves) were for many ages the only people adapted to survive permanently in the northern climate and thus were isolated from the genetic drift that occurred in the tropics from Africa to southeast Asia. Homo Erectus (orcs) and Homo Sapiens (bushmen) would have been regarded as primitive, naked savages to the Neanderthals and were likely avoided until ice ages forced Neanderthals to migrate into the hot southern lands (which must have felt like hell on earth to the cold-adapted Dwarves). When genetic drift did come to the Neanderthal, it destroyed them as a unique race because the hybrids created were taller, more graceful, faster runners and overall more attractive than Dwarves. The hybrids also fused Dwarven brains/technology with the greater socialization and higher birth rates of the bushmen – thus insuring their conquest of Eurasia.

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