View Full Version : Neanderthals not as bright as us

Jean M
03-13-2013, 12:09 PM
I always thought that Neanderthals were rather more limited intellectually than Homo sapiens, but the size of their brains suggested otherwise to some researchers. Now we have a paper out which explains the matter. Neanderthals had bigger eyes, the better to see in cloudy climes. They were adapted to the north. So they had a bigger visual processing region in the brain, leaving less room for higher cognitive function.

Eiluned Pearce, Chris Stringer and R. I. M. Dunbar, New insights into differences in brain organization between Neanderthals and anatomically modern humans (http://rspb.royalsocietypublishing.org/content/280/1758/20130168), Proceedings of the Royal Society B.

Previous research has identified morphological differences between the brains of Neanderthals and anatomically modern humans (AMHs). However, studies using endocasts or the cranium itself are limited to investigating external surface features and the overall size and shape of the brain. A complementary approach uses comparative primate data to estimate the size of internal brain areas. Previous attempts to do this have generally assumed that identical total brain volumes imply identical internal organization. Here, we argue that, in the case of Neanderthals and AMHs, differences in the size of the body and visual system imply differences in organization between the same-sized brains of these two taxa. We show that Neanderthals had significantly larger visual systems than contemporary AMHs (indexed by orbital volume) and that when this, along with their greater body mass, is taken into account, Neanderthals have significantly smaller adjusted endocranial capacities than contemporary AMHs. We discuss possible implications of differing brain organization in terms of social cognition, and consider these in the context of differing abilities to cope with fluctuating resources and cultural maintenance.

This follows on from previous research by two of the same authors: Eiluned Pearce and Robin Dunbar, Latitudinal variation in light levels drives human visual system size (http://rsbl.royalsocietypublishing.org/content/8/1/90.short), Biology Letters, vol. 8, no. 1 (2012), pp. 90-93.

Ambient light levels influence visual system size in birds and primates. Here, we argue that the same is true for humans. Light levels, in terms of both the amount of light hitting the Earth's surface and day length, decrease with increasing latitude. We demonstrate a significant positive relationship between absolute latitude and human orbital volume, an index of eyeball size. Owing to tight scaling between visual system components, this will translate into enlarged visual cortices at higher latitudes. We also show that visual acuity measured under full-daylight conditions is constant across latitudes, indicating that selection for larger visual systems has mitigated the effect of reduced ambient light levels. This provides, to our knowledge, the first support that light levels drive intraspecific variation in visual system size in the human population.

Ian B
03-14-2013, 09:52 AM
Jean, do I understand this to mean that neanderthals were as intelligent as us, but in different ways according to their particular environment? (In the same manner, with respect, that animals do not have the same ability to reason but have other skill sets and abilities that we don't).

Jean M
03-14-2013, 10:35 AM
I use the term "intelligence" in the typical dictionary definition "ability to comprehend and reason." Intelligence can be contrasted to "instinct", in which certain responses to the environment are in-built. Intelligence enables learning from interaction with the environment and so permits a more flexible response. The ability to communicate enhances the possibilities of communal responses to the environment, and learning from other members of the group.

All species of animal on this earth, including ours, have built-in instincts (e.g. to eat) that ensure their survival. All species of animal on this earth, including ours, have been shaped by natural selection to better adapt to living in specific environments. But some species have adapted more than others towards higher brain functions which enable greater flexibility in response to environment, which makes them more likely to survive in changing conditions, and better able to spread beyond a single ecological niche. We are not the only species with learning ability and some form of communication. It is a matter of degree.

This is a cost-benefit balance. Humankind has sacrificed the ability of many species to produce young which do not require any parental care at all, or which can at least run with the herd within an hour or so of birth, in favour of investing prolonged effort into child-rearing to produce offspring who can wander the world. See also Human Brains Develop Wiring Slowly, Differing from Chimps (http://www.anthrogenica.com/showthread.php?350-Human-Brains-Develop-Wiring-Slowly-Differing-from-Chimps).

Neanderthals had adapted physically to their northern environment. Humankind by contrast invented the needle (warm, tailored clothing) and projectile weapons which could kill mammoth and such-like at long-range (less dangerous).

Jean M
03-14-2013, 11:14 AM
Now that we have the genomes of Neanderthals and a Denisovan, scientists are starting to look at the genetics behind the evolution of the human brain. Matthias Meyer et al., A high-coverage genome sequence from an archaic Denisovan individual (http://www.sciencemag.org/content/338/6104/222), Science, Vol. 338 no. 6104 (October 2012) pp. 222-226 made some preliminary comments.

One way to identify changes that may have functional consequences is to focus on sites that are highly conserved among primates and that have changed on the modern human lineage after separation from Denisovan ancestors. We note that, among the 23 most conserved positions affected by amino acid changes .... eight affect genes that are associated with brain function or nervous system development (NOVA1, SLITRK1, KATNA1, LUZP1, ARHGAP32, ADSL, HTR2B, and CNTNAP2). Four of these are involved in axonal and dendritic growth (SLITRK1 and KATNA1) and synaptic transmission (ARHGAP32 and HTR2B), and two have been implicated in autism (ADSL and CNTNAP2). CNTNAP2 is also associated with susceptibility to language disorders (27) and is particularly noteworthy as it is one of the few genes known to be regulated by FOXP2, a transcription factor involved in language and speech development as well as synaptic plasticity (28). It is thus tempting to speculate that crucial aspects of synaptic transmission may have changed in modern humans.

Jean M
03-14-2013, 07:12 PM
And another paper by Chris Stringer, this time with J. R. Stewart, looks at the demise of the Neanderthals in a slightly different way, though still with a focus on their adaptation to the icy north. Human Evolution Out of Africa: The Role of Refugia and Climate Change (http://dx.doi.org/10.1126/science.1215627), Science, Vol. 335 no. 6074 (16 March 2012), pp. 1317-1321. Their abstract is not as informative as the press release from Bournemouth University, the source for this article: Refugia and Ice Age evolution (http://www.pasthorizonspr.com/index.php/archives/03/2013/refugia-and-ice-age-evolution) (see the original for interesting artwork):

Though the most drastic evolutionary changes occur over long spans of time, the effects of these changes can be seen relatively recently, argues Dr John Stewart, a Senior Lecturer in Palaeoenvironmental Reconstruction & Environmental Change at Bournemouth University.... Stewart took existing knowledge of the geographical spread of plant and animal species throughout the warming and cooling periods during the recent Ice Ages to provide insights into modern human evolution as well as the extinction of Neanderthals and other related species. Neanderthals lived from over 200,000 to about 30,000 years ago and evolved in Europe and Asia while modern humans (Homo sapiens)

Stewart’s claim that climate change caused the Neanderthals’ demise is supported by the work of Love Dalén at the Swedish Museum of Natural History in Stockholm, who has looked at the genes found in 13 Neanderthal fossils from southern Europe and western Asia. All Neanderthal fossils more than 48,000 years old, and those found in Asia, had a higher level of genetic diversity than later European fossils, suggesting that the Neanderthals probably went through an evolutionary ‘bottleneck’ where a significant percentage of the population perished. When a bottleneck occurs, the remaining individuals are often a less diverse group, which makes it difficult for them to evolve and adapt to a changing environment as the potential for change is lessened within the DNA itself.

Previous research into other animals such as hedgehogs and polar bears suggest that, even once an Ice Age ends and the different populations start intermingling again, they never really merge back together as a single group. This process drives important evolutionary changes, which can ultimately lead to the origins of a new species – and the extinction of others. Ultimately, this explains why Homo sapiens are still here and our archaic human cousins went extinct some 30,000 years ago: our ancestors were in a refugium that allowed greater evolutionary scope, with less chance of genetic bottlenecking.

03-14-2013, 11:19 PM
What is your opinion about this, Jean?

Jean M
03-14-2013, 11:45 PM
Yes I saw the Wood 2013 study just in time to revise my text. This makes the Neanderthal tool-kit dated between 31 and 34 thousand years ago at Byzovaya, in subarctic Russia, the latest survival in Europe.

03-16-2013, 07:51 PM
Interesting find, but your title is editorializing, Jean. We can say that their larger brains are likely due to a larger emphasis on processing visual information, but they could have still been about as bright.

Jean M
03-16-2013, 11:34 PM
The evidence suggests not, Ezana. The deduction from the study cited in my first post is that "Neanderthals have significantly smaller adjusted endocranial capacities than contemporary AMHs." The study goes on to discuss the implications of that for "differing abilities to cope with fluctuating resources and cultural maintenance." My thread title reflects the opinions of the authors of the study (as well as my own).

There has been a lot of debate over the years over which cultural artefacts were produced by Neanderthals and which by Anatomically Modern Humans. Several authors have wanted to attribute certain cultures (e.g. Uluzzian) to Neanderthals and then argue from the culture that the Neanderthals had developed "modern" behaviours independently of Homo sapiens. This idea is now under attack from various directions. Teeth from Grotta del Cavallo, southern Italy (Uluzzian Culture), have been recently reclassified as Homo sapiens (Benazzi 2011*). And as I say, genetic evidence is emerging of intellectual differences.

* Benazzi, S. et al. 2011, Early dispersal of modern humans in Europe and implications for Neanderthal behaviour (http://www.nature.com/nature/journal/v479/n7374/full/nature10617.html), Nature, 479, 525–528.

03-17-2013, 02:59 AM
The evidence suggests not, Ezana.
Ezana is exactly correct that we have no persuasive evidence that Neanderthals had any less intelligence than humans of roughly the same timeframe--only speculation based on suppositions. Not a single Neanderthal has taken a modern IQ test. (Not that I trust IQ tests to measure intelligence anyway.)

Let's put this another way: If Mark Thomas were to apply his acidic tongue unbiasedly, he would call Pearce an astrologist. That is not a criticism of Pearce's paper, but of Thomas's letter.

Ironically, Pearce could provide at least some evidence for his hypothesis by showing a strong, consistent correlation between the intelligence of modern humans and the size of their eye sockets. Did he actually do this, or did he decide that such an experiment would be politically incorrect?

Here's more irony: Pearce is quite literally embracing phrenology, which Wikipedia calls a "pseudoscience."

Phrenology (from Greek: φρήν, phrēn, "mind"; and λόγος, logos, "knowledge") is a pseudoscience primarily focused on measurements of the human skull, based on the concept that the brain is the organ of the mind, and that certain brain areas have localized, specific functions or modules. The distinguishing feature of phrenology is the idea that the sizes of brain areas were meaningful and could be inferred by examining the skull of an individual. Following the materialist notions of mental functions originating in the brain, phrenologists believed that human conduct could best be understood in neurological rather than philosophical or religious terms.

Jean M
03-17-2013, 01:36 PM
Ironically, Pearce could provide at least some evidence for his hypothesis by showing a strong, consistent correlation between the intelligence of modern humans and the size of their eye

You misunderstand the paper, which presents the opposite conclusion, or rather argues for no such correlation. Eiluned Pearce (who is female by the way) points out that birds and primates who need to see in the dark or poor light have large eyes and a correspondingly large visual centre in the brain (to process the incoming data). Think of owls or galagos (http://en.wikipedia.org/wiki/Galago).

She moved on from that to humans. It has been noticed that people living in northern latitudes have on average larger brains. Does that mean that they are brighter than people in warmer climates? No. She argues that (http://rsbl.royalsocietypublishing.org/content/8/1/90.full) it means that they have (on average) developed larger eyes and a correspondingly larger visual cortex to cope with lower light levels. That makes their brain bigger without improving their IQ. This explodes a racist myth.

Now the latest paper presents the same argument in relation to Neanderthals, who had a long time to become adapted to life in the north. They had larger eye sockets than Anatomically Modern Humans, and larger cranial capacity. When you allow for the enlarged visual cortex and larger body mass, the Neanderthals actually had less space in the brain for symbolic thinking etc than AMHs.

This undermines the argument by Cochran and Harpending 2009 that interbreeding between incoming AMHs and Neanderthals in Europe conveyed some magical genetic ingredient to Europeans which shot forward their cultural development, as witnessed (they claim) by the birth of art in the Upper Paleolithic. In reality, art was not invented in Europe. Early painting simply survives better in Europe because at least some of it was protected by being on deep cave walls, rather than out in the open. As for conveying some genetic intellectual advantage - that looks like a complete non-starter from the genome comparisons so far.

03-20-2013, 03:58 AM
Neanderthals lived from over 200,000 to about 30,000 years ago and evolved in Europe and Asia while modern humans (Homo sapiens)

Is this the currently accepted date for origins of Neandertals? I recall reading estimates closer to 400,000 years and possibly older.

Regarding Neanderthals better vision - I wonder if we can speculate that they might have hunted at night. Given that they hunted large mammals with spears at close range, perhaps it might have been safer to hunt at night or poor light conditions.

Jean M
03-20-2013, 07:18 PM
Is this the currently accepted date for origins of Neandertals? I recall reading estimates closer to 400,000 years and possibly older.

Various dates have been given Gail. Stewart and Stringer 2012 avoid controversy by saying "There is consensus that Neandertals (Homo neanderthalensis) occupied the west of the continent for more than 200,000 years..". Hublin 2009 discusses the upper (600,000 ka) and lower dates and points out that "An intermediate hypothesis proposes that the population separation time occurred between 500 and 400 ka." So I went for the lower end of the intermediate date.

Jean M
06-06-2013, 02:36 PM
I have only just noticed the BBC coverage of the paper first mentioned on this thread. Pallab Ghosh, Neanderthals' large eyes 'caused their demise' (http://www.bbc.co.uk/news/science-environment-21759233) (click for link). It explains the matter very clearly:

A study of Neanderthal skulls suggests that they became extinct because they had larger eyes than our species. As a result, more of their brains were devoted to seeing in the long, dark nights in Europe, at the expense of high-level processing. By contrast, the larger frontal brain regions of Homo sapiens led to the fashioning of warmer clothes and the development of larger social networks.... The research team explored the idea that the ancestor of Neanderthals left Africa and had to adapt to the longer, darker nights and murkier days of Europe. The result was that Neanderthals evolved larger eyes and a much larger visual processing area at the backs of their brains.

The humans that stayed in Africa, on the other hand, continued to enjoy bright and beautiful days and so had no need for such an adaption. Instead, these people, our ancestors, evolved their frontal lobes, associated with higher-level thinking, before they spread across the globe.

Eiluned Pearce of Oxford University decided to check this theory. She compared the skulls of 32 Homo sapiens and 13 Neanderthals. Ms Pearce found that Neanderthals had significantly larger eye sockets - by an average of 6mm from top to bottom. Although this seems like a small amount, she said that it was enough for Neanderthals to use significantly more of their brains to process visual information.

"Since Neanderthals evolved at higher latitudes, more of the Neanderthal brain would have been dedicated to vision and body control, leaving less brain to deal with other functions like social networking," she told BBC News. This is a view backed by Prof Chris Stringer, who was also involved in the research and is an expert in human origins at the Natural History Museum in London....

The finding runs counter to the idea that Neanderthals were not the stupid, brutish creatures portrayed in Hollywood films; they may well have been as intelligent as our species. Oxford University's Prof Robin Dunbar, who supervised the study, said that the team wanted to avoid restoring the stereotypical image of Neanderthals. "They were very, very smart, but not quite in the same league as Homo sapiens," he told BBC News. "That difference might have been enough to tip the balance when things were beginning to get tough at the end of the last ice age," he said.