Average Cranium/ Brain Size of Homo neanderthalensis vs. Homo sapiens

Keely Clinton B.S., Department of Biology, Howard University


Introduction

All humans on Earth are classified as Homo sapiens, also known as modern humans. This species of humans evolved 200,000 years ago. Initial theories presented evolution as a lineage where homo sapiens derived from Homo neanderthalensis who lived on earth from 250,000 to 30, 000 years ago. Recent studies have proven that Homo neanderthal and Homo sapiens existed at the same time with one another. In fact, evidence suggests that the advancement of Homo sapiens is accountable for the demise of Homo neanderthal. It is most likely, both species descended from Homo heidelbergensis who lived approximately 700,000 to 200,000 years ago and was the first of early humans to use fireand spears, and build shelters out of wood and rock.

While Homo heidelbergensis is the known ancestor of Homo neanderthal and Homo sapiens the evolution of modern humans dates back much farther. Prior to early humans it is has been known that humans have a relation to great apes which has been proven by genetic information. In the study of evolution, DNA is the most important component in being able to explore the difference between one species and another. While the genetic difference between individual humans today is minuscule – about 0.1%, on average – study of the same aspects of the chimpanzee genome indicates a difference of about 1.2%. The bonobo (Pan paniscus), the close cousin of chimpanzees (Pan troglodytes), differs from humans to the same degree. The DNA difference with gorillas, another African ape, is about 1.6%. Most importantly, chimpanzees, bonobos, and humans all show this same amount of difference from gorillas. A difference of 3.1% distinguishes us and the African apes from the Asian great ape, the orangutan (Smithsonian, National Museum of Natural History, 2015).

Humans belong to the biological group known as Primates, and are classified with the great apes, one of the major groups of the primate evolutionary tree. Besides similarities in anatomy and behavior, our close biological kinship with other primate species is indicated by DNA evidence. It confirms that our closest living biological relatives are chimpanzees and bonobos. But we did not evolve directly from any primates living today.DNA shows that our species and chimpanzees diverged from a common ancestor species that lived between 8 and 6 million years ago. The last common ancestor of monkeys and apes lived about 25 million years ago (Smithsonian, National Museum of Natural History, 2015).

Figure 1: Significant excavations of early and modern humans

Figure 1: Significant excavations of early and modern humans

Discussion

Who is Homo neanderthalensis?

The name Homo neanderthalensis can be broken down with each word. Homo, is a Latin word meaning ‘human’ or ‘man’. Neanderthalensis is based on the location where the first major specimen was discovered in 1856, the Neander Valley in Germany. The German word for valley is ‘Tal’ although in the 1800s it was spelt ‘Thal’. Altogether Homo neanderthalensis therefore means ‘Human from the Neander Valley’. Hundreds of Neanderthal fossils have been found since the first identified in 1856 in the Neander Valley, Germany. Some defining features of the species include the large middle part of the face, angled cheekbones, and a huge nose for humidifying and warming cold, dry air. They had large brains and short, stocky physiques suited to living in cold environments. Their bodies were shorter and stockier than ours, another adaptation to living in cold environments. The average height of males was 5 ft. 5 in. (164 cm), weighing on average 143 lbs (65 kg). For females the average height was 5 ft. 1 in. (155 cm) and 119 lbs (54 kg) (Dorey, 2014).

Neanderthal bones are thick and heavy and show signs of powerful muscle attachments. Neanderthals most likely would have been extraordinarily strong by modern standards, and their skeletons show that they endured brutally hard lives. This species consisted of skilled hunter-gatherers, made and used flint and stone tools, built shelters and controlled fire. They were highly carnivorous, but they also ate other foods. There is limited evidence of plant food survival in the archaeological record. The number of plant foods Neanderthals could eat would have dropped significantly during the winter of colder climates, forcing Neanderthals to exploit other food options like meat more heavily. There is also evidence that Neanderthals were specialized seasonal hunters, eating animals were available at the time (i.e. reindeer in the winter and red deer in the summer). In Mediterranean regions, the Neanderthals exploited marine resources such as shellfish and seals, but their use of aquatic foods was certainly more limited than that of modern humans (Natural History Museum, 2015).

Neanderthals made and used a diverse set of sophisticated tools, controlled fire, lived in shelters, made and wore clothing, were skilled hunters of large animals and also ate plant foods, and occasionally made symbolic or ornamental objects. There is evidence that Neanderthals deliberately buried their dead and occasionally even marked their graves with offerings, such as flowers. No other primates, and no earlier human species, had ever practiced this sophisticated and symbolic behavior.

The Neanderthal genome project was founded in July 2006 by the Max Planck Institute Institute for Evolutionary Anthropology in Germany with the purpose of sequencing the Neanderthal genome. As previously mentioned, genetic data by this team suggest that Neanderthals shared a common ancestor with our species around 400,000 years ago, thought by many scientists to be Homo heidelbergensis. Neanderthals and modern humans belong to the same genus, Homo, and inhabited the same geographic areas in Asia for 30,000–50,000 years. Genetic evidence indicate while they may have interbred with non-African modern humans, they are separate branches of the human family tree (separate species). For about 70,000 years, Neanderthals roamed Earth with modern Homo sapiens. Fossil evidence from the Middle East suggests that our ancestors not only lived at the same time as Neanderthals, but probably lived alongside them in some areas. Results showed that people in Europe, Asia and New Guinea have around 2.5% Neanderthal DNA in their genetic code, suggesting Neanderthals interbred with modern humans not long after they spread out of Africa (Figure 1).

The “out of Africa” theory supports the idea that modern humans evolved relatively recently in Africa, migrated into Eurasia and replaced all populations which had descended from Homo erectus. The "out of Africa" hypothesis says that Neanderthals were no match for the better-adapted, quicker-witted Homo sapiens. They were out-competed, pushed out of their habitats, and ultimately driven to extinction by a superior species, Homo sapiens. Newly discovered evidence suggests another possibility, lending some credibility to a hypothesis that has languished in relative obscurity for as long as "out of Africa" has reigned. The "multiregional" hypothesis is the messy alternative. It says that pockets of Homo sapiens left Africa not in one large, unstoppable wave, but in smaller movements across many different regions. The hypothesis goes further to suggest that Neanderthals didn't actually go anywhere, but were instead subsumed into the various populations of Homo sapiens. This scenario implies that

Neanderthals were so closely related to Homo sapiens, a subspecies, that they interbred and mixed gene pools with our own. Yet another alternative theory suggests that Ice Age climate fluctuations affected European flora and fauna, causing the disappearance of familiar plants and animals, and that modern humans were better able to adapt than Neanderthals. With the reason for the disappearance unclear, one thing we are sure of is all physical evidence of the Neanderthals disappeared around 30,000 years ago (Brown, 2015).

Cranial/ Brain Size of Homo Neanderthalensis

Many people are under the misconception that Homo neanderthal had a smaller brain than modern humans since they were not as evolved. But their brains were just as large as ours and often larger, proportional to their brawnier bodies. Homo neanderthal brain size was larger than the average modern human brain and averaged 1500 cubic centimetres and an average 3.3 lbs. This is to be expected, as Neanderthals were generally heavier and more muscular than modern humans. People that live in cold climates also tend to have larger brains than those living in warm climates.

Homo neanderthal had a distinctive skull shape that was long and low, with a rounded braincase. The back of the skull had a bulge called the occipital bun and a depression (the suprainiac fossa) for the attachment of strong neck muscles. The skull was thick but rounded brow ridge lay under a relatively flat and receding forehead. Homo neanderthal possessed a mid-face region that showed a characteristic forward projection, this resulted in a face that looked like it had been ‘pulled’ forward by the nose. The orbits were large and rounded with a nose that was broad and very large (Australian Museum, 2015) (Figure 2).

Figure 2: Comparison of species to cranium configuration  

Figure 2: Comparison of species to cranium configuration

 

Brain Function of Homo Neanderthalensis

Scientists have the fossilized skulls the Neanderthals left behind to decipher information about the brain and its function, which isn’t extremely helpful. Anthropologists now know that they used tools, made art, and may have talked.  Still, nobody fully knows how their brains worked, or how their thinking was different from modern day humans. Fresh analysis of fossil data suggests that their brain structure was rather different. Although the brains of our ancestors and Neanderthals were about the same size, Neanderthals had larger brain areas related to vision and body control. Homo Neanderthalensis seem to have adopted an alternative strategy that involved enhanced vision coupled with retention of the physical robusticity of H. heidelbergensis, but not superior social cognition. Results imply that larger areas of the Neanderthal brain, compared to the modern human brain, were given over to vision and movement and this left less room for the higher level thinking required to form large social groups. For example, if the Neanderthals had less brain area devoted to social cognition, it might explain why they traveled shorter distances, had fewer symbolic artifacts and lived in smaller communities.

“Neanderthals had smaller social networks than modern humans because Neanderthals had smaller areas in their brains to deal with social complexity,”    says investigator Eiluned Pierce.

Smaller social groups is an aspect of Neanderthal explaining why Neanderthals went extinct whereas modern humans survived hence many theories surrounding this observation. Smaller social groups might have made Neanderthals less able to cope with the difficulties of their harsh Eurasian environments, because they would have had fewer friends to help them out in times of need (Fenlon, 2013).

Once the differences in body and visual system size are taken into account, researchers are able to compare how much of the brain was left over for other cognitive functions. Research by the Oxford scientists shows that modern humans living at higher latitudes evolved bigger vision areas in the brain to cope with the low light levels. This latest study builds on that research, suggesting that Neanderthals probably had larger eyes than contemporary humans because they evolved in Europe, whereas contemporary humans had only recently emerged from lower latitude Africa. Because this study is based on a hypothesis it is important to note certain regions are specialized to process certain types of sensory inputs and are active during certain tasks. But they’re all part of distributed functional networks, and we’re nowhere near understanding how those networks lead to this or that behavior. Scientists must always be careful about how to interpret any particular finding. In this case, the study shows a contrast between the visual systems of Neanderthals and our ancestors. That could underlie a difference in their social processing, or it could very well not (University of Oxford, 2015).

Who are Homo sapiens?

The name Homo sapiens, selected for ourselves means ‘wise human’. Homo is the Latin word for ‘human’ or ‘man’ and sapiens is derived from a Latin word that means ‘wise’ or ‘astute’. Homo sapiens is the name given to our species if we are considered a subspecies of a larger group. This name is used by those that describe the specimen from Herto, Ethiopia as Homo sapiens idàltuor by those who believed that modern humans and the Neanderthals were members of the same species. (The Neanderthals were called Homo sapiens neanderthalensis in this scheme). Homo sapiens evolved in Africa from Homo heidelbergensis. They co-existed for a long time in Europe and the Middle East with the Neanderthals, and possibly with Homo erectus in Asia and Homo floresiensis in Indonesia, but are now the only surviving human species. African fossils provide the best evidence for the evolutionary transition from Homo heidelbergensis to archaic Homo sapiens and then to early modern Homo sapiens. There is some difficulty in placing many of the transitional specimens into a particular species, because they have a mixture of intermediate features which are especially apparent in the sizes and shapes of the forehead, brow ridge and face. Some suggest the name Homo helmei for these intermediate specimens that represent populations on the brink of becoming modern. Late surviving populations of archaic Homo sapiens and Homo heidelbergensis lived alongside early modern Homo sapiens before disappearing from the fossil record by about 100,000 years ago (Australian Museum, 2015).

The earliest Homo sapiens had bodies with short, slender trunks and long limbs. These body proportions are an adaptation for surviving in tropical regions due to the greater proportion of skin surface available for cooling the body. More stocky builds gradually evolved when populations spread to cooler regions, as an adaptation that helped the body retain heat. Modern humans now have an average height of about 160 centimetres in females and 175 centimetres in males.

Cranial/ Brain Size of Homo Sapiens

Homo sapiens living today have an average brain size of about 1350 cubic centimetres which makes up 2.2% of our body weight making the brains of this species absolutely smaller than those of Homo neanderthalensis. However, due to its gracile postcranial skeleton,  the brain of Homo sapiens is larger relative to body size than that of Homo neanderthalensis. Early Homo sapiens, however, had slightly larger brains at nearly 1500 cubic centimetres. The skulls of modern Homo sapiens have a short base and a high braincase. Unlike other species of Homo, the skull is broadest at the top and the sides of the skull are nearly vertical. The fuller braincase also results in almost no post-orbital constriction or narrowing behind the eye sockets. The back of the skull is rounded and indicates a reduction in neck muscles. The face of Homo sapiens is reasonably small with a projecting nose bone. They also have a limited brow ridge and the forehead is tall with orbits that are square rather than round. The skull of Homo sapiensgenerally lacks evidence of being strongly built (e.g., it lacks the large brow ridges and bony prominences seen in Homo neanderthalensis and Homo heidelbergensis) (Australian Museum, 2015) (Figure 3).

As early humans faced new environmental challenges and evolved bigger bodies, they evolved larger and more complex brains. Large, complex brains can process and store a lot of information. That was a big advantage to early humans in their social interactions and encounters with unfamiliar habitats. These unique features of Homo sapiens including changes in the skull and postcranial skeleton suggest changes in brain size and architecture and an adaptation to tropical environments. Over the course of human evolution, brain size tripled. The modern human brain is the largest and most complex of any living primate.

These anatomical changes are linked to cognitive and behavioral changes that are equally unique among hominin species.  In particular, the archaeological evidence of behaviors thought to be unique to Homo sapiens, which appear first in Africa around 170,000 years ago, highlight the importance of symbolism, complex cognitive behaviors, and a broad subsistence strategy.

Even within the last 100,000 years, the long-term trends towards smaller molars and decreased robustness can be discerned. The face, jaw and teeth of Mesolithic humans (about 10,000 years ago) are about 10% more robust than ours. Upper Paleolithic humans (about 30,000 years ago) are about 20 to 30% more robust than the modern condition in Europe and Asia. These are considered modern humans, although they are sometimes termed "primitive". Interestingly, some modern humans (aboriginal Australians) have tooth sizes more typical of archaic sapiens. The smallest tooth sizes are found in those areas where food-processing techniques have been used for the longest time. This is a probable example of natural selection which has occurred within the last 10,000 years (Brace 1983).

Figure 3: The skull of Homo sapiens versus skull of Homo neanderthalensis

Figure 3: The skull of Homo sapiens versus skull of Homo neanderthalensis

Figure 3: The skull of Homo sapiens versus skull of Homo neanderthalensis

Brain Function of Homo sapiens

Since the last common ancestor shared by modern humans, chimpanzees and bonobos, the lineage leading to Homo sapiens has undergone a substantial change in brain size and organization. The last common ancestor can be reconstructed displayed several unique phylogenetic specializations of development, anatomical organization, and biochemical function.  These neuroanatomical substrates contributed to the enhancement of behavioral flexibility and social cognition. With this evolutionary history as precursor, the modern human mind may be conceived as a mosaic of traits inherited from a common ancestry with our close relatives, along with the addition of evolutionary specializations within particular domains. Anatomical and molecular changes have also been identified that might relate to the greater metabolic demand and enhanced synaptic plasticity of modern human brain's. Finally, the unique brain growth trajectory of modern humans has made a significant contribution to our species’ cognitive and linguistic abilities (Dunbar, 1996).

While increased brain size, comprising mostly growth of the neocortex (Finlay and Darlington, 1995), undoubtedly has been central to the evolution of modern human cognition, other modifications to brain development, structure, and function are also certain to be significant. Subtle modifications in neural microstructure and gene expression can have a significant impact on behavior, even in the absence of large-scale changes in the size of brain parts (Hammock and Young, 2005). Therefore, evolutionary processes can mold behavioral phenotypes using a host of strategies (Stromberg, 2013).

Studies have also suggested that the internal organization of Neanderthal brains differed significantly from modern humans. While Neanderthal had a larger visual cortex dedicated to interpreting visual information, Homo sapiens developed structures beneficial for social advancement. This divergence in mental capacity for higher cognition and social networking, the researcher argue, could have led to the wildly different fates of H. sapiens and Neanderthals.

“Having less brain available to manage the social world has profound implications for the Neanderthals’ ability to maintain extended trading networks,” Robin Dunbar, one of the co-authors, said in a press statement (Stromberg, 2013).

Genes related to Evolution of Higher Brain Function

Scientists have been working to discover the genes that led to the rapid expansion of the human neocortex. Two recent reports have identified candidate genes. So far scientists at the Max Planck Institute have identified 56 candidate genes that are “unique” to humans in the sense that they are the products of recent gene duplication. When a gene is duplicated, it is a powerful evolutionary change, because one copy is free to mutate and acquire new functions, while the other copy retains whatever vital function that the original gene performs. In this way, an escape of the usual rule that mutations are almost always harmful, because they result in a defective gene. With two copies, random tinkering caused by mutations is tolerated, opening up new avenues for innovation (NHL, 2015).

One gene that was found was ARHGAP11B which is expressed in regions of the human brain that are uniquely huge. To prove its significance researchers inserted this gene into mice to record its expression. The mice developed brains with larger neocorticies and their entire cerebral cortex developed the grooves and folds, called sulci and gyri, found in the brains of higher animals (typically smooth in rodents) (NHL, 2015).

Researchers at Duke University performed an experiment on a gene enhancer specific to humans, HARE5. HARE5 was selected from a list of noncoding elements found to be different between humans and chimps because it controls the expression of a gene known to be involved in nervous system development, the Wnt receptor FZD8, making it a good candidate for influencing the evolution of the human brain. Scientists again inserted this genetic info into mice, which resulted in mice with bigger brains due to larger neocortices. These mice also showed the primate-like grooves and folds in their neocortices. This confirms the role of this noncoding genetic element in the expansion of the primate brain( NHL, 2015).

 

Conclusion

Across the board we can see the vast similarities and distinct differences between Homo neanderthalensis and Homo sapiens with one of the most significant comparisons being mental capacity. Having such a close relationship, existing at the same time with each other we see many similarities in the brain function such as communication abilities, use of fire and tools and also habitat building. These elements are specific to the genus Homo demonstrating a commonality within and a difference from other primates. The difference in brain function between the two are extremely important, so much so that it is the reason that one species survived and the other did not. Cognitive ability and social development happened to be the deciding factors dictating which population was better fit for the environment. With this information we may be able to move forward in looking at ways to forward progression of human intelligence and fitness. By knowing which genes are responsible for our present development we can predict the best future genetic make up for ourselves.

 

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Keely Clinton B.S. completed her undergraduate career at Benedict College and is a Doctoral Student at Howard University. Read More >


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