Homo 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 ofHomo 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 thesocial 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 |
| The neanderthal data has yet to be published and will be included here when it is/when I find it |
No comments:
Post a Comment