Evolutionary Tales Behind Ötzi’s Mesocephalic Skull
Any migratory link of short headedness or ‘brachycephaly’ with the Neolithic advance can be excluded. The lack of any eastern – or northern – shift in the DNA of Ötzi, as observed in my previous post on the subject, should be enough to falsify all assertions accumulated in scientific history about an eastern origin of the ‘modern’ tendency towards shorter brains. This certainly doesn’t support any link either with a theorized ‘extended expansion’ of kurganized populations in the Bronze Age. Ötzi’s DNA was absolutely ‘western’, even more so than current European populations whose genetic gravity seems to have shifted predominantly towards a more northern signature nowadays – especially in Central Europe, where Ötzi is from.
Peculiar, therefore, was Ötzi’s moderately short, ‘mesocephalic’ skull shape, still rare in his time. Intermediate between the traditional ‘long-headed’ shapes, and innovative ‘short-‘, or ’round-headed’ shapes, these skulls start to pop up in the European record – indeed! – about the time of Ötzi. Bernhard (1994) described his skull thus:
[The length-breadth-index] of the mummy’s skull is mesocranic, i.e. of medium length in relation to the breadth of skull. The skull is relatively high (akrocranic) compared to its breadth (Bernhard, 1994)
According to the anthropological criteria of the Frankfurt Agreement (1882), the Cranial Index (CI) of Ötzi (CI = 75.9) was still far from being brachcephalic (short headed, CI over 80) and just slightly too short for being dolichocephalic (long-headed, CI up to 74.9). In the French system his skull classifies as ‘Subdolichocephalic’, indicating his departure from the pre-Neolithic dolichocephalic past indeed meant only slightly shorter, in agreement with the proposition that Ötzi represents the first onset towards the short modern brain.
Indeed, an eastern origin of brachycephaly is problematic in many ways. It can’t be simply deduced from current nor past populations anywhere. Neolithic populations were hardly any less dolichocephalous than Mesolithic aboriginals, even in the supposed Neolithic homelands in the Middle East. The European appearance about 3000 BC of ‘alpine’ round-headedness, often accompanied by a flat ‘dinaric’ occiput, was sudden and contrasted with an older mediterranean-nordic phenotype. So far, no reliable relationship between culture and phenotype could be established, even though in Western Europe this cranial modification was often linked with the introduction of Bell Beaker culture. The Iberian pensinsula, another candidate for the hypothetized homeland of Bell Beaker, was certainly not the origin of dinaric or alpine types: shorter skulls could only be confirmed in a few Portuguese burials, Mallorca and a few dubious cases in the Meseta and the levante (Lichardus), while their presence in Catalonian megaliths rather preceded immigrant maritime and regional Beaker styles.
Another line of thought makes the association with Bronze Age mountaineers that descended to the lowlands to sell their ores, probably based on a purported – though unsupported – theory that brachycephaly was a new adaptation against colder climates in mountainous regions. In Greece such a mountainous origin may indeed fit the evidence: according to Dienekes, Panagiaris’ study (1993) on the Ancient Greek population “from a physical anthropological perspective (413 male and 354 female crania, using 65 biometric characters as well odontological traits)”, concluded that “the greater period of discontinuity in the material is observed during the Helladic period (=Bronze Age in Greek archaeology), where broad-headed incoming groups appear, side by side with the older Mediterranean population” (Dienekes, July 22, 2012). Actually, the period mentioned in the text for this change to be already noticeable was Protohelladic, about 3000 BC, ie. only a few centuries later than Ötzi (3370-3100 cal.BC – Kutschera, 2001):
From the Neolithic to Hellenistic times, in the Helladic space, we find as dominant element the mediterranean genetic substratum
The greatest migration of population which took place in ancient times seems to have happened during the Bronze Age, and it is characterized by a genetic flow from mountainous populations of Pindos towards the southern main part of Greece. The culmination in the intensity of these processes took place during the Early Bronze Age (Protohelladic) and the first half of the Middle Bronze Age (Mesohelladic). (Panagiaris, 1993)
No tendencies to this extend can be detected in the pre-Neolithic human fossil record, not even during the Ice-Age. Almost contemporaneously also non-European phenotypes passed through this quite radical change, towards an world-wide emergence of brachycephaly. Non-dolichocephalic types were quite new, despite Ötzi even to the Alps, while in the Carpatian Basin, even though broad-headedness is nowadays considered native in these regions, their introduction had to wait for the arrival of the Western European Bell-Beaker culture.
Interestingly, amidst a predominantly long-headed population, intrusive brachycephalic elements already reached the northern Italian Remedello and Rinaldone cultures shortly before the advance of Bell Beaker. Ötzi’s mesocephaly could thus as well have been due to hybridization with southern neighbors and indeed, Ötzi’s measurements groups best with these northern Italians (Bernhard 1994). Next in line are representatives of the contemporaneous Horgen culture in eastern Switzerland, that is often linked with the Seine-Oise-Marne (or SOM) culture. Surprisingly, this was one of those regions that allegedly constituted a strong brachycephalous bearing at an early stage. Some Neolithic-period continuity of a brachycephalous element is suggested for the region between Rhine and Seine.
Post-war clashes of grand ideologies that defined the past, during the most insane century of humanity ever, still have their effect on 21st century science. Taboos on phenotype evidence caused much once carefully collected information to be now ignored, avoided or simply lost. However, brachycephalic remains at Furfooz, Belgic Ardennes, originally claimed to be Magdalenian by Dupont (1872), are nowadays rather considered Neolithic (Charles, 1996), thus contradicting previous statements that Furfooz – and brachycephaly – constitued another Upper Paleolithic element in Europe next to the long-headed Cro Magnon and the prognathic Grimaldi types. Coexistence in the European landscape of profoundly different phenotypes over a longer period remains unattested until the Neolithic, and if so the close-range genetic differentiation and isolation implied would have been a remarkable feat in human evolution. More reliable Neolithic results were first found in Grenelle, west of Paris. Munro (1899) mentioned the ‘highly brachycephalic’ type of two skulls found in the cavern of Tertre-Guerin (Seine-et-Marne), and sixteen brachycephalic skulls out of thirty-three from a series of sepulchral caverns at Hastiere in Belgium. The former belonged to an advanced neolithic culture that practised trepanning, and produced polished stone celts, with and without horn-casings. Their culture is arbitrarily dated between 3300-2700 BC, mainly to comply with the more secure dates of the related Horgen culture in Switzerland. Though culturally important, so far this closely related complex located in more mountainous territory couldn’t be credited with the origin of brachycephaly either.
Any association with an immigrant racial component, new in (West and Central) Europe and potentially accompanied by new dominant genetic markers, is highly hypothetical. Bell Beaker culture was often linked with Y-chromosomes marked by haplogroup R1b, that in a recent investigation on ancient DNA could already be confirmed in some very old samples recovered from a site in Kromsdorf, northeast of Weimar in Thuringia (Lee et al., 2012). The ultimate origin of this marker is hypothetized to have been somewhere else, though at least the current European distribution is most likely the result of a long term process rather than impelling migrational events that could be readily identified in the archeological record. Grand conclusions on a distant origin can’t be established for a very common European marker whose distribution rather reveals the remnants of an older European dichotomy in R1b (Morelli et al., 2010). Even the physical type of Bell Beaker folks results unlikely to indicate anything more than rather weak exogenetic admixtures.
Actually, the origin of brachycephaly is elusive and all points to a quite modern, homoplastic innovation. This skull type represents the clearest departure from Cro Magnon’s occipital bun, allegedly inherited from Neanderthal. Indeed, Lohring Brace claims that the Upper Paleolithic and subsequent Mesolithic of northwest Europe simply developed there in situ out of Neanderthal precursors. However, subsequent changes of the skull were dramatic. The origin of those changes are impossible to localize, but apparently accelerated in regions where increased levels of gene flow could be expected. Some places were hit harder by the change than others:
The craniofacial form of Cro-Magnon allies with the living populations of northwestern Europe, specifically with the fringes in Scandinavia and England, but not with the European continent.
Everything from the details of mastoid process form and nuchal muscle attachments to fully “bun-shaped” occiputs demonstrates a continuity from Neanderthal morphology to what visible in the inhabitants of the fringes of western Europe today in Norway, the Faeroe Islands, and England […] Given those aspects of occipital morphology in living northwest Europeans, one would have to predict fossil ancestors with a similar configuration. Fossil predecessors exist with the right occipital characteristics […], and they are called Neanderthals. (Brace, 1996)
The demise of the bun is remarkable, since the occipito-temporal region counts as ‘one of the most derived anatomical areas in the evolution of the Neanderthal lineage’ (Rosas et al., 2008). Migrationists typically pulled their own migrational rabbit out of the hat for their explanations, but all they could offer was some faint notion of an Asiatic source – for having a strong presence of brachycephaly nowadays. Noteworthy is that early Asiatic specimens typically miss any tendency towards brachycephaly, and featured dolichocephalic as anywhere else. Back in time the development of Asiatic skulls parallels Europe even in the occipital bun, a feature of the lost Peking man fossils, still reminiscent in the ~20-30 kya Liujiang hominin (Ash & Robinson, 2011) – despite Liujiang’s already much more rounded occiput having an angularity of 122º, ie. well within the diagnostic range of modern humans (above 114º). If such reduced angularity of the occiput preluded the emergence of shorter skulls at all it should be noted this tendency was observed already in some early sapiens near Israel’s Qafzeh cave, dated to 96-115,000 B.P. Interpreted as ‘modern’ rather than ‘racial’, the remarkable variation of the feature was attributed to sexual dimorphism in the occiput rather than the involvement of a round headed hominin in what could have been a racial hybridization event: a flexed occipital that carries a torus-like bulge centrally (Skhul IX) was interpreted as ‘male’ while an evenly rounded occiput with no development of a transverse torus (eg. Qafzeh 9) was interpreted as ‘female’. This kind of sexual dimorphism is unknown among modern humans and neither does this derive from preceding hominins, as illustrated by the pre-Sapiens paleodemes found in Spain at the Sima de los Huesos, Sierra de Atapuerca. Though considered part of the paleospecies ‘Homo Heidelbergensis’ that forked into the Neanderthal and African Sapiens lineages (‘A conservative minimum estimate for the age of the fossils is now said to be 530 Ka’ – Rightmare 2008), their sexual dimorphism is rather diagnosed by size differences comparable to recent populations. The ‘purity’ of early sapiens in the Near East was never sufficiently questioned, while actually they roamed the frontier between Neanderthal and African hominins, each having cranial characteristics of their own. Still, none of these early differences may seriously be associated with modern brachycephaly, or reveal its origin. Angled occipitals and dolichocephaly were still common among the victims of the Tell Brak killing field, early Neolithic Syria. Senyurek (1951d, pp. 614-15) concluded that “the majority of the Chalcolithic and Copper Age inhabitants of Anatolia were dolichocephals of mainly Eurafrican and Mediterranean types, and that the brachycephals, probably representing the invaders, were rare in these periods. This study has further supported the conclusion that the earliest inhabitants of Anatolia were longheaded, and that the brachycephals came in subsequently.” The alleged introduction of brachycephaly in Mesopotamia during the subsequent Sumerian period, as represented in art, was never confirmed by actual finds:
[…] in iconography the Sumerians were represented with short heads, while the skulls found at Ur and all other sites were long (Soltysiak, 2004)
This ‘Sumerian problem’ of a Mesopotamian population devoid of attested brachycephaly, while originally being characterised by dolichocephaly, appears to be part of an international ‘Brachycephaly problem’. Hittite planocciputs in Anatolian art dates from much later, is equally unsupported by corresponding skulls and postdates the ‘Bell Beaker problem’ of brachycephaly in the west. Only this year a similar tendency was described for Bronze Age Crete, essentially unrelated to marked historical events:
Therefore these results suggest a gradual rounding of the cranial shape for the Central Cretan population in the course of the Bronze Age, resulting from the increase of the cranial breadth in relation to cranial length. They further provide negative evidence for a disruption of the biological history of the Knossos population following the LMIB destructions due to an increase in the biodistance between the samples dating immediately prior and following the destructions.
The gradual rounding of the cranial shape of the Central Cretan population over the course of the Bronze Age and the very similar shape of the Gypsades, Sellopoulo and Mavrospelio crania can be more clearly appreciated by plotting the Cranial Index (100*maximum cranial breadth/glabello – occipital length) data. The Cranial Index describes the cranial shape and higher cranial indices reflect a more rounded cranium. […]
The gradual increase in Cranial Index over the Bronze Age most probably reflects gene-flow from populations biologically different from the Early Bronze Age Cretan population and from inter-population biological interactions (admixture) in the succeeding periods. (Nafplioti, 2012)
Assumed Neolithic intrusions from outside, of populations very different from the European native populations, have been a pitfall for genetic investigators before. Genetic investigation on Neolithic skeletons failed to support the traditional view of Neolithic migrants leaving a dominant imprint on the current European population. Even though assumed essentially non-European, their Neolithic genetic contribution must have suffocated amidst apparent Mesolithic influences in a process already explained as Mesolithization elsewhere on this blog. Moreover, at least the cultural package of LBK, the main “intrusive” Neolithic complex in northern Europe, seems to have developed in Hungary before it spread on the North European plain. The initial advent of the Neolithic LBK groups was swift and influential, but within four centuries there was a decline. The Rossen, Bischheim and Michelsberg cultures developed from LBK stock and apparently their material culture was much appreciated over a wider area, but this success eventually petered out when territorial expansion turned into stagnation. In general there was a noticeable environmental adaptation that inherited from a more Mesolithic way of life. In turn, the acceptance of Neolithic elements within the communities of their Mesolithic neighbors can’t be attributed to anything else but induced inspiration. Many elements of the TRB, a more natively-inspired Neolithic culture, seem to originate in Mesolithic contexts, even though the proximity of the LBK heritage must have been decisive for their appearance. Notwithstanding adaptive processes and the emergence of a completely new physical type, the demise of the Neolithic component seems closely connected with Mesolithization and hence, the resilience of pre-Neolithic populations that in traditional archeology was lost out of sight.
Speculation on an eastern origin of the planocciput remains without evidence, though the despair for finding a geographic origin in the east still rings through contemporary publications:
A. Wierciñski, contrary to the earlier authors, found a far more complicated anthropological structure in the Mesopotamian population, which made the previous search for [a brachycephalic] “Sumerian race” pointless. In his opinion the area of Tibet (or generally Central Asia) may be considered as the Sumerians’ place of origin. (Soltysiak, 2004)
Planoccipital (‘flat’) skulls definitely postdate ancestral AMH areas and remain absent in pre-Neolithic contexts as far as Eastern Asia. Everywhere the deviation from dolichocephaly seems to be a fairly recent development.
Indeed, for all we know, brachycephaly only started to increase in the Late Neolithic and apparently still continues to do so. Whatever the origin, only the success of Bell Beaker apparently turned brachycephaly into an important ethnic marker. Hooton (1947) described Bell Beaker as ‘a Nordic-Alpine cross grown taller and more rugged than either parental races through hybrid vigour’. Coon pointed out the formative blend didn’t occur in Britain since there the brachycephalous Alpine element, an essential ingredient, was still lacking. The nasal convexity and occasionally flattened occiput of the Bell Beaker type was perhaps qualified more correctly by Coon as Dinaric, though this doesn’t resolve the Bell Beaker origin either. Some Dinaric-like characteristics may indeed be reminiscent to admixtures dragged into the west during the Neolithic, though their ultimate origin remains unresolved.
Even in the Carpatian Basin, where Dinaric traits still prevail nowadays, this physical type has a rather recent history:
[…] the appearance of the characteristic planoccipital Taurid type, unknown until then from the Carpathian Basin, in the populations of some later cultures (e.g. Kisapostag and Gáta-Wieselburg cultures) suggests a mixture [of Bell Beaker people] with the local population (Zoffmann, 2000)
The Dinaric type was no less the result of dinarization in the wider region of the Carpatian Basin as anywhere else. Evolution may be involved, possibly triggered by a Neolithic tipping point to be associated with cultural developments that vastly surpassed geographic and ethnic boundaries. The cultural link may be illustratied by late-holocene tendencies towards a new custom of cranial deformation, to the result of occipital flattening and (hyper)brachycephaly. Possibly there is a reverse relationship:
A suggestion was that the beginning of artificial cranial deformation was linked to the first appearance of brachycephaly during the Upper Palaeolithic period and a desire of prehistoric men to continue with a preceding “longhead tradition” (Zivanovic, 1982) – Arensburg et al., 1988
Examples of this fashion pop up first in a wide range of Neolithic societies. Remarkably, the alleged cultural isolation of the Americas, already contradicted by contemporaneous Neolithic culture, is turned on its head by the practice of cranial deformation that once flourished with an incidence of 90% of the total population in some regions. The possible relation to real brachycephaly is eg. corroborated by the reported association of the practice of cranial deformation with Armenians and Pueblo Indians. Brachycephaly is represented today in the midwest and among many of the northwestern tribes, especially, though not exclusively, associated with Na-Dené languages. This group allegedly belongs to the much broader Dené–Caucasian superfamily, which also contains the North Caucasian languages, Sino-Tibetan languages, and Yeniseian languages, thus establishing the only major linguistic connection of populations on both sides of the Bering Sea. Large linguistic families are commonly associated with more advanced cultural groupings and at least the Na-Dené grouping on the Eurasian side are remarkable for their often ancient link with the Neolithic way of life. A chain of cultures thus appears to have participated in both cranial deformation and the holocene transition towards brachycephaly and Neolithic culture. Cranial deformation was fashionable in the Yeniseaian contact zone of Dené–Caucasian and the Afanasevo culture, often considered ancestral to the Tocharian branch of Indo-European populations. The custom also penetrated into the largely contemporaneous North-West Caspian steppe area in Russia, populated by the allegedly Indo-European Catacomb culture more to the west. Dating issues of human bones previously attributed an excessive age to both cultures, due to lower 14C values on their attested ‘fluvial’ menu compared to terrestal samples. Only nowadays such an enigmatic eastern origin can be dismissed in favor of a quick eastward expansion of Indo-European cultures, reaching Afanasevo territory not before 2500 BC – thus indeed being slightly younger than Catacomb culture.
Most 14C dates of human bones of the Early Catacomb and East Manych Catacomb culture are older than expected. […] The consumption of river food is the basis of the reservoir effect in the collagen of human bone.
Using these corrections, we conclude that the historical time interval for the Early Catacomb culture is 2600–2350 cal BC, instead of 3300/2900–2450 cal BC, and for the East Manych Catacomb culture is 2500–2000 cal BC, instead of 2900/2800–2300 cal BC. (Shishlina et al., 2007)
Indo European culture and populations travelled west to east in Asia, making it even more remarkable that cranial deformation apparently travelled in opposite direction. Or maybe the fashion was older along the Atlantic rim and part of the transition of Mediterranean and Atlantic megalithic cultures to Bell Beaker culture? In Malta this cultural change was indeed accompanied by the first western attestation of cranial deformation.
Whatever happened, at the end the once well-established Cro-Magnon type simply disappeared:
Basques and Canary Islanders are clearly associated with modern Europeans. When canonical variates are plotted, neither sample ties in with Cro-Magnon as was once suggested. (Brace, 2005)
Next to cranial deformation, a truly ‘evolutionary’ origin of brachycephalic skulls may have been obscured by another environmental, ie. epigenetic element. Plasticity can be demonstrated by historic fluctuations of the cranial index (a ratio of skull length to width):
[…] factors such as climate, as well as cultural change (such as increased tool development and use) might have led to changes in skull morphology in late Neolithic/early Bronze Age Britain (Brodie 1994:80)
Brodie and other researchers found that: Cranial Index does seem to correlate positively with temperature and negatively with humidity
Brodie speculated that Neolithic cranial morphology was influenced by these cold, damp conditions. In contrast, during the early Bronze Age (2480 cal BC- 1450 cal BC), the climate was apparently drier. Brodie argues that as a result, the gradual increase in the Cranial Index which occurred in northwestern Europe during the Neolithic and early Bronze Age could have been in response to climatic improvement (Bartels, 1998)
These climatological fluctuations can’t explain wider tendencies towards simultaneous cranial changes in disparate locations, as has been expressed in the investigation on the changes in Crete already mentioned above:
An alternative interpretation implicating the thermoregulatory model of Beals et al. (1984) and adaptation to colder climatic conditions carries less weight. (Nafplioti, 2012)
Whatever the cultural and possibly climatologic causes, accelerated cranial evolution must have been involved. Initially, since Neanderthal, those changes seem to concentrate on enlargements of the frontal lobe, but a profound structural reorganization seems to occur only much later, including the overall brain shape, an increased cerebellum and – remarkably! – a decreased brain mass since 10k years ago. Using new technology, researchers have produced a replica of a 28,000-year-old early modern human, ‘Cro Magnon 1’, that provided further evidence for the theory that the human brain has been shrinking: the brain was found to be about 15-20% larger than our brains.
Mean cerebellum volume in Neandertals (106.35 ~12.32 cm3) is both absolutely and relatively smaller than the mean for recent humans (139.76 ~2.54 cm3). Additionally, a plot of NetBrain against CBLM (Fig. 5) clarifies that CQ in Neandertals is low also because the rest of the brain […] is large, compared with the recent human sample […]. Cro-Magnon 1 […] embodies the archaic pattern of a relatively large NetBrain and a relatively small cerebellum. (Weaver et al., 2005)
The reduction of endocranial capacity of modern humans, except for the cerebellum, is significant and runs counter to the common perception of an evolutionary tendency towards ‘bigger brains’:
[…]within the past 10,000 years the average endocranial volume in European females reduced from a mean of 1502 ml to a recent value of 1241 ml. This decrease of approximately 240 ml in 10,000 years is nearly 36 times the rate of increase during the previous 800,000 years. (Hawks, 2011)
The volume of Ötzi’s brain fits this picture, since despite his short stature (~159 cm) his brain size was still well above the modern average:
With 1535 cm3, it lies markedly above today’s male average of approximately 1450 cm3. (Bernhard, 1994)
Brain size relates mathematically to body size, though this doesn’t diminish the value of a bigger brains. True, studies have found a very small relationship between brain size and intelligence, and many other factors affect brain intelligence. Indeed, some take the reduction as an indication of evolutionary progress of one kind or another:
The evolution of smaller brains in many recent human populations must have resulted from selection upon brain size itself or on other features more highly correlated with brain size than are gross body dimensions (Hawks, 2011)
At least, all seems to indicate that in general brain reduction does not affect mental capacities, with one important exception: the cerebellum:
In the australopithecines and early members of the genus Homo, the cerebral hemispheres were large in proportion to the cerebellum, compared with other hominoids. This trend continued in Middle and Late Pleistocene humans, including Neandertals and Cro-Magnon 1, who have the largest cerebral hemispheres relative to cerebellum volume of any primates, including earlier and Holocene humans. (Weaver, 2005)
Did investigators overlook the possibility that overall brain shrinkage and an increased cerebellum may be interrelated?
The high energy cost of the human brain is generally considered an important evolutionary constraint to brain development:
The energy demands (kcal/g/min) of brain and other neural tissues are extremely high—approximately 16 times that of skeletal muscle. Consequently, the evolution of large brain size in the human lineage came at a very high metabolic cost
Brain metabolism accounts for ~20% to 25% of resting metabolic rate (RMR) in an adult human body. This is far more than the 8% to 10% observed in other primate species and still more than the 3% to 5% allocated to the brain by other (nonprimate) mammals (Leonard et al., 2007)
The extremely high neuron ratio of the cerebellum thus implies an even higher energy cost to humans than the grey matter of the cerebral cortex. For this reason an increased cerebellum would require overall brain reduction to allow humans to remain at the same level of metabolic cost. Genetic correlation of brain size with body mass or stature does not rely on evolutionary changes, so a selective process must have enforced a new energetic trade-off due to the increased cerebellum.
Apparently, some parts of the brain are more easily “compressed” than others. The remarkable increase of the cerebellum in modern humans is incompatable with the traditional view on its function, that merely involved motor control. An evolutionary increase of the cerebellum is nowadays deemed necessary for modern humans, allegedly being congruent to an increase of human skills. It has already been established the cerebellum has a much larger contribution, including linguistic functions:
The precise nature of the cerebellar involvement in linguistic processing is not yet clear.
[…] results led to the clinical awareness of a modulating role of the cerebellum in various language processes.(De Smet et al., 2007)
Other cognitive processes important to modern life may be involved as well, and actually there is nothing ‘inferior’ about the cerebellum to contradict this suspicion:
The cerebellum is a very densely packed and deeply folded subcortical brain structure situated at the back of the brain […] In humans, it accounts for 10-15% of brain weight, 40% of brain surface area, and 50% of the brain’s neurons. (Fawcett & Nicolson, 2008)
We have to be aware, though, that brain reduction may also be part of a simple ‘domestication process’. Down’s syndrome (DS) inborn pathology also features brain reduction averaging ~17% according to Pinter et al., 2001, using a set of apparently low-average comparison subjects. However, DS brain reduction reaches a 33% peak for the cerebellum. Indeed, a flattened occiput symptomatic for Down’s syndrome (DS) can’t even be attributed to a disproportionate reduction of the occipital lobes. Remarkably, DS overall brain reduction compares to that of modern man since Neanderthal and early AMH, and is only truly regressive for the reduced cerebellum.
An increased role of the cerebellum also implies an improved interconnectivity with the cerebral cortex, and related changes to optimize the brain structure towards shorter ‘communication lines’ all the way to the frontal parts implicated in planning complex cognitive behavior, personality expression, decision making and moderating social behavior:
Neuroanatomical studies showed neuronal pathways linking the cerebellum with autonomic, limbic and associative regions of the supratentorial cortex. More specifically, cortical areas send information to the cerebellum via the basilar pons, and deep cerebellar nuclei send information back to prefrontal areas through dentatothalamic pathways (De Smet et al., 2007)
Could this be the secret behind Ötzi’s slightly mesocephalic skull, and the general post-neolithic tendency towards brachycephaly and a flatter occiput? The sudden appearance of cranial deformation is a testimony of the reluctance by which this physical change was received by contemporanous populations. But the costs of an improved brain may have been heavier than beauty. If current differences defined by the Down syndrome may be any indication, collateral ‘damage’ of a shrunken brain could have been in the realm of behavior, such as an individual loss in the capacity of self-determination, or an increased sense of social dependence? – what for sure would be a comfortable advantage to some in a more advanced society that takes care of most of their needs. The contemporaneous reduction of the strong posterior projection in the ‘bun’ of earlier sapiens and Neanderthal may also suggest that overall cerebral reduction may have affected the occipital lobes more than other parts. Since this location is associated with REM sleep and dreaming, it might be tempting to link this specific reduction to the emotionally less complicated rationality necessary to cope with the rapid changes of a Neolithic world. More specifically, would decreased occipital lobes have reduced the importance of dreamed reality in daily life?
So far it is hard to relate cerebellar volume to mental functions or capabilities. Current populations apparently have very similar abilities to “manage complexity,” and studies on the between-group variability of cerebellar volume for living people are rare and incomplete. Tang et al. (2010) reported clearly visible ethnic differences between the Chinese and Caucasian populations, where the former has a relatively shorter but wider brain atlas compared to the widely-used ICBM152 template, based on Caucasian brains. This picture corresponds to more brachycephaly measured in east Asiatic populations. Comparative information on cerebellum volume would be more than welcome to evaluate modern variation.
The apparent inverse relationship between reduced brain mass and increased cerebellum is just one of the many changes in the human physique that seems to have initiated during the Neolithic. Evidence of genetic sweep tends to suggest genetic change was more important after the introduction of agriculture than during the previous Upper Paleolithic transition towards anatomically modern humans. Indeed, the genome of Ötzi already supplied essential insights on the accelerated evolutionary change that hit humanity since the (Late) Neolithic. Likewise, Ötzi’s mesocephaly occurred in this critical period of neuroanatomical change. Hopefully, a thorough investigation on the tissues of Ötzi’s brain will shed more light on the evolutionary mechanisms behind this issue in the near future.
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