Over time evolution has caused a change in cranium size between Neanderthals and humans. Beginning with genetic drift and mutation, changes have occurred throughout time that have led to a much smaller cranium size in modern humans compared to the cranium size of Neanderthals many years ago. About 400,000 years ago, Neanderthals and humans diverged to become genetically distinct likely from the hominid Homo heidelbergensis (Homo heidelbergensis, 2016). The two species developed many differences both physically and behaviorally; one of the interesting traits that evolved to become different between them was the sizes of their crania (i.e. part of skulls that enclose the brain). It was studied that “Neanderthals had significantly larger orbits than modern humans”(Pearce et al, 2013). As well as “larger eyeballs and visual cortices”(Pearce et al, 2013). Along with the visual cortices, the occipital contour (the area where the temporal and occipital lobes meet) is also more pronounced. One of the “most distinguishable features of the human clade is the chin”(Fukase, 2015), but it serves different purposes in humans and Neanderthals. As the temperature on earth started to drop the Neanderthals with larger body builds used less energy to get warmer. This was because Neanderthals with bigger bodies had lower thermoregulatory costs than ones with smaller bodies as their bodies helped insulate the heat and used less energy to keep their bodies warm. If the temperature in the area they lived was a lower average, then Neanderthals with smaller bodies would be expending more energy to keep warm. “Over the past 3.2 million years, there’s been a correlation with larger brains and colder temperatures in the Homo genus”(Naya et al, 2015). Neanderthals were found to live in higher altitudes than modern day humans. Because of the “…northern geographic range of Neanderthals…distinctive features of the Neanderthal cranium are adaptations to the glacial climate”(Weaver et al, 2007). In these higher altitudes the cooler temperatures led to larger skulls because they were more effective at insulating heat. As time went on and evolution shrunk skull size, modern humans traveled down in elevation and learnt how to build fires as other means to heat their bodies and stay warm. Although there is much evidence to support the fact that a human cranium is much smaller than that of the Neanderthal, it is still an unusual fact to wrap your head around. If humans are so much more intelligent then why is the average cranium size so much smaller? It is, “hypothesize(d) that growing smaller but similarly efficient brains might have represented an energetic advantage, which paid off in faster reproductive rates”(Braun, 2009). Neanderthals have also shown to have, “lateral widening but overall flattening of their parietal lobes, whereas (humans) have uniform parietal surface enlargement”(Pearce et al, 2013). Although Neanderthals had larger brains than humans, “they utilized their brains in a different way; while human brains are quite focused on social and cognitive abilities, Neanderthal brains were instead more developed for vision and body movement”(Pearce et al, 2013). Because of this, “humans formed larger social groups while Neanderthals were more individualistic”(Pearce et al, 2013) likely causing “…isolation between Neanderthal and modern human populations [which] would have led to cranial diversification by genetic drift”(Weaver, 2007), by “limiting gene flow between the two species that otherwise had the ability to interbreed”(Currat M and Excoffier L, 2011). Along with the difference in cranium size came the ability of speech. “Neanderthals could have been capable of speech”(D’Anastasio, 2013), but the capability of speech does not translate to functioning social interaction. Neanderthals and humans used similar parts of the body for different purposes. Modern humans used vocal cavities for speech and to communicate, but Neanderthals used teeth and jaws to chew food and had very little communication skills. “Neanderthals also had larger body masses than [humans] and required significant portions of the brain for motor skills”(Pearce et al, 2013). There are many theories as to how the cranium size of Neanderthals grew larger than those of humans. Natural selection, mutation, and genetic drift have all been proposed as possible reasons. It may takes years of hard evidence to prove which theory is correct. Through the vast technology today, and thanks to endocasts, the difference between Neanderthals and humans is always causing new evidence, so as we wait patiently for new evidence to arise we thank evolution for all it has done to increase our fitness.
References
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doi: 10.1073/pnas.1107450108
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