Neanderthal Intelligence and the Sperm Whale Brain

One of the few things we know about the internal organisation of the sperm whale brain is its cerebellar quotient (CQ). That information would be insignificant did it not place this species brain in two unique categories. In all other other cetaceans, including the dwarf sperm whale the CQ > 1 (ie. every other whale and dolphin exceeds the mammalian average): and the sperm whale is the most extreme outlier ever measured among all mammals. Such extremes must have significance, but what? The best clue we have is that its closest CQ match to any other mammal is the neanderthal.

Neanderthals had a small proportion of their brains devoted to lower functions, and a higher cerebral proportion than even modern humans. A few years ago, the consensus was to interpret this as their brain being less balanced and useful than ours. That seems suspiciously like human exceptionalism, so let’s do something many might assume impossible. Let us compare the intelligence of neanderthals and moderns, with attention to the history of the science.

Homo_neanderthalensis

The science of anthropology developed rapidly after Darwin outlined his ideas of natural selection. Ironically, the metaphor of the arrow of progress, which has far more to do with pre-Darwinian evolutionary philosophy, was overemphasized in this new beginning. We survived long after the neanderthal so we must be smarter went that thinking.

Today, there is no need to rely on outdated concepts. We have so many ways to gauge the intelligence of this extinct species, that a series of articles would be justified. Unfortunately, that is hard to justify on a cite devoted to cetacean intelligence, so I will attempt to condense the material.

Behavioural Evidence

Data on the sophistication of tool manufacture, and use of body decoration has been used for a long time, but, until recently, it contained a flaw. The comparison needs to be contemporary versus contemporary. For a long time it looked as if the Cro-Magnons (our direct ancestors in Europe) were significantly more advanced than us during a long period where we lived side-by-side. However, carbon dates in the relevant range are susceptible to distortion by the intrusion of traces of new carbon into old deposits. This bias has been eliminated by new techniques (see New Carbon Dating Suggests Neanderthals and Early Humans Didn’t Mingle Much). After better measures, we are now certain that the overlap of the two species was brief in Europe, and it is very hard to tell which was the more advanced species during that window (see Neanderthals were not less intelligent than modern humans, scientists find).

Not all new behavioural evidence is in favour of the intellectual parity of the two species. There are also lines that suggest neanderthals were far smarter than us. Below are two examples of such evidence.

Neanderthals Defy Stereotypes — NOVA | PBS

and Evidence neanderthals made boats long before modern humans

There is another behavioural factors, of a more general nature, that may also prove important. The Machiavellian intelligence hypothesis places the major evolutionary pressure for building higher intelligence as coming from group interactions. Both archaeological and genetic evidence suggests that neanderthals moved in significantly smaller groups than Cro-Magnons. This indicates they were less social and, if so, we should have a large advantage, but current data does not back the use of group size beyond application to social skills. Actually, if even if we try to force a best fit on our current primate data, the slope goes the wrong way, giving the neanderthals an advantage! (about +10 IQ points).

Dietary Evidence

The link between dietary breadth and primate intelligence is statistically well attested. It should no longer be considered as coincidental that humans have the widest diet of all extant primates, but how do Cro-Magnons and neanderthals compare?

Both species are known to eat a wide variety of plants and animals, but the neanderthal diet is more specialist, tending to be at least 80% meat, and almost all of that coming from a handful of megafauna species. By contrast, the Cro-Magnon diet looks to be only around three quarters plant, and including a wider variety of both plant and meat staples. Very recent discoveries have widened the known neanderthal diet considerably, including some medicinal plants but the best guess probably remains in favour of a Cro-Magnons advantage.

Physiological Evidence

Then there is also physiological evidence. Their brains were significantly larger than ours, though published figures as to how much vary widely. This is partly because so few complete, or almost complete, neanderthal skulls have been found, and they differ significantly from each other. Their brain endocasts seem to be about three standard deviations larger than those of modern humans. Since human IQ correlates about a third with brain size, if we knew nothing else about neanderthals other than brain size, our best guess would be a neanderthal advantage of +15 IQ points. An old idea is that these figures would have to be adjusted for body size, but doing so for primates has been shown to produce very poor results. (see Overall brain size and not encephalization quotient best predicts cognitive ability across non-human primates).

Recently this evidence was joined by that of cranial blood flow. The brains of some primates are more tightly packed with neurons than others, and require proportionately more energy per unit volume. This time, the advantage goes goes to our species by almost 20% (see Fossil skulls reveal that blood flow rate to the brain increased faster than brain volume during human evolution). This would imply that we are the smarter, and since this might be expected to have an even more direct connection to intelligence the magnitude of it would translate to the order of -20 IQ points. An alternative reason for this low neanderthal blood flow goes right to the heart of this post…

Neanderthals have a proportionately smaller cerebellum, where most mammalian neurons are housed. The difference in this between our species is so extreme that it is still quite possible that their cerebral cortex might be more densely packed and ‘hungrier’ than ours. Many have postulated that the cerebral cortex is the true seat of cognisance, and since we can only measure the combined blood-flow to all brain areas, this evidence may prove misleading. To investigate further we must look to genetic evidence.

Genetic Evidence

Even in the absence of any understanding of how neanderthal or modern human genes work we could still gather evidence, by looking at variation within any one ethnic group of modern humans, as long as the individuals within the sample have known proportions of neanderthal DNA. In the better studied populations of Europeans and East Asians the neanderthal proportion can vary in any one individual from 0%, to an unlikely theoretical maximum of circa 20% (see At least 20% of Neanderthal DNA is in Humans). If IQ shows a consistent trend within each group, (ie. average IQ scores trend in the same direction to the same degree as neanderthal DNA proportion of individual genomes increases within all ethnic groups), then we might still gain a clear idea of which species was the smarter. However, it looks as if we will be able to use much more direct evidence than that.

Until recently, the only gene or domain that we knew to be highly correlated to IQ scores was DUF1220. Not only does the copy number of this gene domain correlate with human IQ scores, but it has also been shown to have a very high correlation coefficient when matched to the cognitive skills of non-human primates, and which I have normalised to my primate IQ scale. Neanderthals have 350 copies of it, whereas we average only 278. If we judge from non-human primates and calibrate that gene dose data against primate intelligence, we return an estimated neanderthal advantage of +17 IQ points, but if we judge them as humans it gets trickier. If we treat neanderthals as humans then the CON2 subtype of DUF1220 is far more predictive than CON1 (see DUF1220 copy number is linearly associated with increased cognitive function as measured by total IQ and mathematical aptitude scores). Unfortunately, our current neanderthal genome data is not of sufficient quality to differentiate the two, but assuming they have the same ratio of the two to modern humans, then we may expect they have a +25 IQ point advantage.

A year and a half ago, a far more comprehensive picture of how human genes relate to intelligence in normal healthy subjects appeared. (see Intelligence genes discovered by scientists.) These findings have yet to be applied to neanderthals but, when they are, you can expect a more confident estimate than any of the back-of-the-envelope figures given above.

Summary and Implications

I believe that the current balance of evidence leans in favour of neanderthals superiority, and we can expect more definitive findings soon. This has the potential to uniquely match the direction brain evolution took in the smartest terrestrial species ever known, to the aquatic equivalent that is the subject of this website.

You may have noticed that the methodology I use to get to that conclusion also could be applied more directly to Physeter macrocephalus if only a similar amount of research had been done on that living species, as has been to the study of our dead relative.

 

Posted in brain, Intelligence