Neanderthals had differently organised brains

ResearchBlogging.orgHomo neanderthalensis is not a species to be dismissed lightly. They weren’t especially dumb, nor especially weak. Indeed, they actually had larger brains and denser muscles than we did.

On top of that, their technology was so well adapted to their environment that they were able to flourish without drastically altering it for hundreds of thousands of years. It was just that good.

So it would seem we have no clear advantage over them, which makes the fact we survived but they did not especially puzzling.

Recent research argues this might have been because their brain, despite being bigger, ultimately had a more primitive shape. Our frontal and temporal lobes are a different to theirs and our olfactory bulb is larger. Could our brain shape have given us an advantage?

Now, new information presented at the HOBET conference I recently attended lends further credibility to that hypothesis.

Admitting I went to an EvoAnth conference sounded a lot cooler in my head…

Earlier research has identified that there is a link between eye-socket size and eyeball size (no duh) and that there is in turn a link between eyeball size and visual cortex size.

Whilst this might seem like a bit of a “captain obvious” moment, this work also identified something rather interesting: eye-socket size is correlated with latitude.

The further away from the equator, the larger the eye-socket of an individual was. This likely has something to do with the fact that the amount of light from the sun gets lower the further north/south one travels, thus an increase in eyeball size would help maintain good vision in the darkening environment.

Positing light levels as the cause of this variation in eyeball size instead of say, neutral mutations, gains support from the fact that visual acuity remains the same across latitudes, instead of decreasing with the lower light levels as one would expect if these enlarged eyeballs were simply neutral variants.

In other words, they caught evolution in action.

I want a picture of Darwin with a sly smile for these occassions

The presentation at HOBET built upon this information by including in the eye-socket of Homo neanderthalensis. Being a species that lived in the north for a longer period than Homo sapiens, one would expect them to have larger eyeballs than us. This means that they should have also had a larger visual cortex than us.

So using the statistics the earlier research had gathered, they estimated the size of the neanderthal visual cortex and subtracted it from the total brain size, leaving them with the size of the bits of the brain relevant to intelligence.

Surprisingly, this figure was smaller than that of members of Homo sapiens from the same period (after they too had been corrected for visual cortex size), suggesting that the neanderthals’ bigger brain gave them no intellectual advantage over us.

From the original research, establising a link between latitude and eye-socket size (orbital volume)

Indeed, their reduced brain size might well have put them at a disadvantage. When the group size of Homo neanderthalensis was calculated from this new figure and the correlation between group size and brain size established by the social brain hypothesis it was found that they would’ve lived in smaller groups than Homo sapiens.

Further, when compared to the correlation between “levels of intentionality” and brain size it was found that neanderthals would’ve only been able to reach 4th level intentionality!

Now, despite being followed an exclamation point you probably don’t understand the significance of levels of intentionality so let me explain. Each level of intentionality is understanding an additional person thinks something.

When writing Othello, Shakespeare had to understand [1] the audience would think [2] that Iago intended [3] that Othello would believe [4] that Desdemona wanted [5] to love another for his plot to work.

So Homo neanderthalensis could’ve only reached part 4 of Othello. Ultimately what this means is that they would’ve had less complex social groups, a further disadvantage on-top of their smaller group size.

Also, there could’ve been no neanderthal Shakespeare.

Which is a shame because I think he would look quite fetching in mammoth skin

However, the data on which the intentionality/brain size correlation is based off is rather poor, having being gathered from only 3 animal species. Further, neanderthals seem to be very close to the threshold of being able to have 5th level intentionality so the refinement of these statistics with more data may well push them over that limit.

Also – as I said earlier – humans had larger occiptial bulbs. Perhaps if one were to also control for this (and any other “irrelevant” parts of the brain) our brain sizes might be brought back into alignment after all.

On-top of that, the visual cortex isn’t completely divorced from intelligence; with it apparently being associated with various mathematical abilities. So concluding neanderthals were below us intellectually by removing the visual cortex might well be an incorrect conclusion.

That said, the correlation between brain size (without visual cortex) and group size is well established so concluding they did live in smaller groups would likely be correct.

Another piece in the neanderthal puzzle has been discovered.

Pearce, E., & Dunbar, R. (2011). Latitudinal variation in light levels drives human visual system size Biology Letters, 8 (1), 90-93 DOI: 10.1098/rsbl.2011.0570
Pearce, E., Stringer, C., & Dunbar, R. I. M. (2013). New insights into differences in brain organization between Neanderthals and anatomically modern humans. Proceedings of the Royal Society B: Biological Sciences, 280(1758)
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22 thoughts on “Neanderthals had differently organised brains

    • Well the new stuff from HOBET hasn’t been published yet (or at least, I haven’t been able to find it) and so I can’t tell you what it was based on unfortunately. I’ll be sure to update you when I find out.

  1. Pingback: Neanderthals had differently organised brains | Science News | Scoop.it

  2. But the most recent scientific studies have determine that all humans of European descent also have Neanderthal DNA but those from Africa do not. How is it that we carry them in our bodies and yet you surmise they died out?

    • We do have neanderthal DNA, but it’s a very small amount. So small, in fact, that it could’ve been caused by a single occurrence of interbreeding between us and them.

      Given such a small quantity of DNA, I’m not prepared to start proclaiming they secretly live on in us.

  3. Pingback: Neanderthals had differently organised brains | Aux origines | Scoop.it

  4. The post informs about some interesting developments that unfortunately i dont share at all.

    Let me explain.

    In order to work animal hides Neanderthals:

    -gathered lithic raw material, transported it miles away, worked it in different shapes for different functions (see below);
    -gathered bitumen, transported it miles away, modified it with fire and water;
    -gathered mineral ochres, transported them miles away, worked them with lithic tools and water;
    -gathered wooden sticks, modified them with different lithic tools;
    Gathered vegetable or animal strings/fibers;

    then they made composite tools using the bitumen, the strings, the wood, and yet another different >/i>lithic tools.
    All that in order to yet another objective: To provide clothing and shelter (hide-working objective).

    Of course if we add to that system the complexes techniques of lithic raw material knapping, tool configuration, trasnportation, use, re-sharpening and recycling of tools, then we find a certain scenario of undeniable complexity, quite similar to many H-G societies from the recent past (in fact, the neandertal technology has been judged as much more complex that the technology of many H-G groups from the recent past).

    Thats why i find that all this talking about brain size and levels of intentionality is quite futile. I think that more pausible hypotesis need be developed , because all this concept of simple Neandertals makes no senso on the light of the archaeological record of his human behaviour.

    • It would seem that many aspects of intelligence don’t have a direct relationship with brain size, but group size does. As such, this study doesn’t suggest that they were particularly stupid or unable to create complex tools, but simply that they could only maintain smaller groups.

      • Its only that the “inference” of a limitation in the amount of those so-called “levels of intentionaly” in neandertal behaviour seems to me unrealistic.

        Specially, on the light of the archaeological evidence related to the very same behaviour, (wich is social, technical and economical -you may prefer subsistential or adaptative- at a time).

        On other issues, all the linkage between eye sockets, brain area size, cognitive functions, etc, while talking an human fosil population, in order to make “inferences” about behaviour… well… it looks highly speculative from my point of view. I dont cry against the exploration of new hypotesis, but i just dont understand why some researchers make all those speculative constructions without making an in-deep look at the reality of the archaeological record. Doing so will be, from my point of view, highly constructive.

        Yet another point: while it has been a “on vogue” assumption during the last couple of years, there’s no evidence of neandertal populations having smaller group size and/or smaller social networks than most of the rest of the contemporary human populations (like most contemporary AMH). Also, DNA analysis of spanish neandertals is showing a typical structure of patrilocal residence/patrilocaly, and systematic women transfer between groups (we’re talking of at minimun of 4 diferent grps sincronically involved at a given time, and that’s the information we have with ONLY 6 subjetcs), which is the very same social basic standar of dozens if not hundreds of recent H-G grps.

        • Well they seemed fairly confident the archaeological record supported their position, citing that neanderthals used resources gathered from a smaller area suggesting limited intergroup trading. They may well be wrong on this fact and if the specifics of the evidence they cite when they eventually publish are incorrect then I invite you to point out how. I’m no expert and will happily defer appraisal to you.

          Although, regardless of the archaeological record there does remain this connection between brain size and at least one tier of group size. So this data seems to suggest that tier is smaller in neanderthals, although the group levels above and below this (i.e. typical “village” size) might well be identical to that of humans.

          Given how similar we seem to be to neanderthals, people are grabbing any difference they can to explain why we survived but they did not and so such a difference in group size will inevitably be posited as a reason. Indeed, given how important groups are to h/g survival there may even be some merit to this suggestion.

          However, if it does turn out there is little archaeological record of such variation in group sizes then it may well be the difference between us and neanderthals is insignificant and not the reason for our differential survival.

    • I didn’t think that many people thought neandethals were simple, and it is aaffirmed that they had complex ways of life.

      I thought this article was pointing out that on a social level they weren’t as complex as us, and that might be why we gained the upper hand.

  5. Pingback: Neanderthal Brains and Eye Size « Bayesian Investor Blog

  6. Interesting read but large eye size isn’t due to longer periods of living in the North for long periods of time. If that were true Eskimos should have much larger eyes than Africans which isn’t the case.

    Interesting read though.

    • The measurements for Innuits are suprisingly absent from the analysis, so it isn’t possible to refute your suggestion. However, the fact that he variation between the different groups was only a milimetre or so (and thus wouldn’t be noticable to the naked eye) undermines the foundation of yourn point

    • Presumably north is just a proxy for variability in illumination. So when you are comparing areas with heavy vegetation then it seems reasonable that illumination is more variable the further north you go. Of course, as you noticed there is the obvious limit, once you are so far north that there is no vegetation, light sources become much less variable. Maybe this is why the far north groups like Innuits were excluded from the analysis.

      • I just realised, it’s probably because at the hyper-far north the sun is reflected off the snow, to the extent that extremely northern populations have a problem with too much light. The Innuit even manufacture “sunglasses” of a sort to deal with this problem.

        Given the glacial periods resulting in snow etc. further south, this may well confound the results of this study.

  7. Is this the reference on this work?

    Pearce, E., Stringer, C., & Dunbar, R. I. M. (2013). New insights into differences in brain organization between Neanderthals and anatomically modern humans. Proceedings of the Royal Society B: Biological Sciences, 280(1758).

    Good to see you reporting the work so much earlier than the slow review process!

    Keven Poulin recently wrote on TheEGG about the social brain hypothesis, and a discussion started about Neanderthals. I was wondering if you could contribute your expert opinion!

  8. An interesting read, but personally, I’m not sure why people don’t focus on the diet aspect of the argument more. From what I understand, there are a couple isolated cases of Neanderthal bones being associated with plant material that may have been eaten (I believe there is a single instance in which one was discovered with cooked seeds in his teeth). In contrast, at least according to what I’ve read, their poop tells us that they were able to digest meat much more efficiently than we are, which points to an adaptation towards carnivory. Given that they are now being analyzed as ambush predators in woodlands and wooded highlands (with their shorter lower legs that would aid in running around mountainous terrain), doesn’t it make sense that, if they were in fact carnivorous, their populations would always have been small simply because they required twice the caloric intake that we do to support their robust bodies, and such a caloric intake would be immediately reliant on a fluctuating environment to provide them with prey?

    I mean, that’s IF they were in fact hypercarnivorous, but with the efficiency with which I’ve heard that they could digest meat, I’m inclined to think that they were. I think that this needs a lot more research, because to me, positing that differences in diet were ultimately responsible for their demise seems a lot more plausible than minor differences in their brain wiring. Because even if they were less socially sophisticated, one would expect that they would have at least survived longer given their wide range. A hunter-gatherer life style with small, simple social groups shouldn’t be THAT unsustainable, in my opinion anyways.

    • The evidence for eating pants comes from two sites, one in Belgium and one in Israel. The researchers picked such far apart sites to show that it wasn’t a localised phenomena but a widespread practice. What’s more, the Neanderthals at these sites were eating every edible plant in their environment, suggesting it was a significant part of their lifestyle.

      However, the evidence suggests meat was still the dominant component of their diet, and that they needed more calories as a result of their physiology. Whilst the picture is more nuanced than the classic “Neanderthal eat big mammoth”, you are basically correct in your summary. They ate a lot of meat and needed a lot of calories.

      This has prompted many to suggest that this may be why Neanderthals went extinct. If they needed a lot of calories then they may not have been able to deal with humans arriving in Europe and taking some of their food. That’s a possibility I discuss in later posts on Neanderthal extinction

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