What in God's name is it?! It's often cited in my anthro classes as a unique characteristic of Neanderthals, but it's never explained. Well, you're all very lucky that I braved the molehill of articles that touch on this subject, from which I gleaned competing speculations and inconclusive findings. The best I could find came from Daniel Lieberman, I'll paste some snippets from my term paper on this (which I started the night before it was due). Abbreviated Introduction - The finds in Tabun and Skhul, both in Israel in 1939, have led to competing hypotheses about the phylogenetic relationships between H.sapiens and H. neanderthalensis. The more recent Skhul remains are characteristic of more modern sapient morphology, thus leading to the hypothesis that H. neanderthalensis evolved into H. sapiens (Day, 1986:118). The archaic H. sapiens individuals found in Mladec, Czech Republic overlap in time with late Neanderthals and possess marked occipital buns. However, Electron Spin Resonance dates for Near Eastern remains show Tabun Neanderthal to be contemporaneous with modern sapient looking human remains from Skhul and Qafzeh (Stringer et al) Therefore, the Near East Neanderthals could not have been ancestors of the H. sapiens in that region. By now, differences in morphology are the main guiding light for phylogenetic placements. Still, there is one more resource that is discovered in 1998 – mitochondrial DNA. The mtDNA of an apparently mixed Neanderthal/Cro-Magnon child discovered in Lapedo, Portugal in 1998 have yielded evidence that the Neanderthal and H. sapiens lines diverged 550,000 to 690,000 years ago. Therefore Neanderthals could not be on the direct line to humans because evidence for their existence is found at the earliest to be 300,000 years ago (Enstam, 2005). Yet, the multi-regional hypothesis is still championed by a handful of anthropologists, who base their hypothesis on morphological continuity in single regions through time. One such example of this morphological continuity is occipital bunning. Supporters of the multi-regional hypothesis claim that the occipital bunning seen in Neanderthal remains is the same as the occipital bunning seen in later archaic H. sapiens remains and humans today. Therefore, the logic goes, it is a sign that it was inherited from Neanderthals (Lieberman, 1995). What is an occipital bun? “A posteriorly-directed projection of the occipital beyond the nuchal plane that results in a distinctive swollen morphology when viewed in norma lateralis. Occipital projection is evaluated primarily from the internal occipital table relative to the internal occipital protruberance (IOP) and to lambda (L).” (Lieberman, 2000) Who has them? Neanderthals, Anatomically Modern Humans (see Mladec 1 & 5, & Cromagnon), Present day humans – high occurrence among Europeans (esp. Lapps & Finns), Bushmen (e.g. Ashanti), & Australian Aborigines Why do they develop? 1. Lieberman (2002) Lieberman proposed that it might have something to do with the bio-mechanics of running. When you run, your head has a tendency to jolt forward, so in order to see well, you have to keep your head steady. Neanderthals have an especially hard time of it, with such a heavy, prognathic face. Lieberman suspects that the Neanderthal’s occipital bun evolved to solve the problem by counterbalancing the large, heavy face. 2. Smith & Green (1991) Smith & Green hypothesize that occipital bunning is due to accelerated development in Neanderthals. They see this process as part of a broader adaptive strategy – earlier development (prenatal even) as a sign of increased reliance on morphology (versus culture) in a harsh environment. 3. Wolpoff Wolfpoff has “suggested that one effect, and possibly one cause, of large occipital buns among the Neandertals was to increase the effectiveness of their nuchal muscles. It is possible that occipital bunning provided a more horizontal, and thus an effectively larger, attachment area of the nuchal muscles…however, the primary determinant in the formation of an occipital bun is probably cerebral growth, since the nuchal musculature would affect mainly the exocranial surface.” – Trinkaus & LeMay, 1982 4. Geist (1978) Geist hypothesizes that “If great strength, agility, and precision and speed of bodily movements were required for such a hunting technique, those parts of the brain controlling motor functions in the hunter had to be greatly developed. Neanderthal possessed a massive cerebellum and motor cortex compared to modern humans. This pulled the brain case rearward, creating an occiput that reached farther rearward than in modern humans, explaining, in part, the large, long, low brain case and bun-shaped occiput of the Neanderthals.” How do they develop? Researchers have used H. sapiens as a referential model for craniofacial growth in H. neanderthalensis. The assumption is that they inherited the same basic pattern of brain development from a common ancestor (Churchill, 1998). In modern humans, the brain grows posteriorly and superiorly, with the lamboid suture fusing last (Trinkaus & LeMay, 1982). Thus, the occipital lobe expands upward and back, resulting in a projecting occiput, as the cranial vault bones suture last. All of the human crania with occipital buns used in Lieberman’s study (2000) come from large-brained, dolichocephalic individuals. That is, individuals with narrow cranial base who have large brains are long-headed because “the narrow cranial bases constrain the degree of lateral expansion of the cranial vault.” Bunning would occur when there is especially rapid growth of the brain relative to formation of the cranial vault bones (Trinkaus & LeMay). However, the buns seen in early anatomically modern humans are not the same in morphology as Neanderthal buns. They are “hemi-buns,” as Smith (1984) has called them. The buns of Neanderthals have a much greater degree of internal table concavity than those of any H. sapiens. Instead, the markedness of the early a.m humans might be due to the thickness of cranial vault bones that characterizes all Pleistocene populations. Also, Neanderthals have wide cranial bases, indicating that some other factors of basicranial growth, perhaps in timing, may account for this difference (Lieberman 2000). Conclusions: The occipital buns seen in H. sapiens are not homologous in morphology or development to the occipital buns in H. neanderthalensis. Cautions: This is a tentative conclusion because the H. sapiens cranium with the largest bun was not included in the study since it was missing its cranial base (Cromagnon 3). Also, the Mladec crania possessed wide cranial bases, some comparable to Neanderthals. Still, the morphology differs in significant ways, indicating that this is a “convergent, epigenetic trait in large-brained, dolichocephalic individuals and not homologous between Neanderthals and some modern early humans” (Lieberman 1995). So, major studies with empirical evidence have thus far shown that 1) Occipital bunning in Neanderthals is at least in part a secondarily developed in relation to primary neurocranial and basicranial growth, which account for other unique Neanderthal traits. 2) Occipital bunning in Neanderthals cannot be wholly explained by the explored growth factors and it is uncertain whether it may possess some adaptive significance, which these missing factors could point to. 3) Neither the development nor morphology of occipital buns in Neanderthals is homologous with that occipital buns in H. sapiens (Lieberman, 2000). This leads us to my final investigation of broader phylogenetic implications. Specifically, I will discuss the implications of my findings on occipital bunning for the two most popular hypotheses for human evolution – Regional Continuity and Out of Africa. Lieberman (1995) gives a thoughtful discussion of phylogenetic analysis in just this context. He stresses the importance of using developmentally homologous traits that are also synapomorphies. Wolpoff, Smith, and Green have put forth occipital bunning as a synapomorphy that proves the ancestor-descendant relationship between H. neanderthalensis and H. sapiens in Europe. However, Lieberman has shown that it is a homoplasy and that “this character underscores the similarities in the narrow cranial base of convergent, epigenetic trait in large-brained dolichocephalic individuals and if anything, Europeans, Australians, and some Africans predicted by the RA hypothesis.” Lieberman admits that cladistic analysis, such as this one, is inherently problematic as it relies on the principle of maximum parsimony. Thus, though a useful tool, parsimony can exclude phylogenetic models that may indeed be correct. Parsimony also assumes that homology is more common than convergence, thus a trait such as this one can slip in undetected. A better method, and the ultimate goal of such evaluations, is to use traits that are “unlikely to be convergent.” This entails a consideration of a trait’s development and function, rather than simply appearance. Conclusion: Thus I have evaluated the trait of occipital bunning and found it to be at the least phylogenetically uninformative, and at best evidence indirectly supportive of the recent-African hypothesis. Key Literature Cited for anyone interested: •Churchill, Steven E. (1998) Cold adaptation, Heterochrony, and Neanderthals. Evolutionary Anthropology: Issues, News, and Reviews. 7:40-60. •Day, M.H. Guide to Fossil Man, 4th ed. Chicago, Illinois:Univ. of Chicago Press, 1986. •Lieberman, Daniel E. (1995) Testing Hypotheses about recent human evolution from skulls. Current Anthropology. 36:159-197. • “Neanderthals on Trial” Narr. Joe Morton. Speakers: Lieberman, D. E.; Bramble, D.; Richmond, B. NOVA. PBS. WGBH, Boston.1/22/02 Transcript. •Lieberman, D.E.; Mowbray, K.M.; Osbjorn, P.M. (2000) Basicranial influence on overall cranial shape. Journal of Human Evolution. 38:291-315. •Smith, F.H. & Green, M.D. (1991). Heterochrony, life history, and Neandertal morphology. American Journal of Physical Anthropology. Supplement 12, 164 (abstract). •Trinkaus, Erik. (1986). The Neanderthals and Modern Human Origins. Annual Review of Anthroplogy. 15:193-218. •Trinkaus, E., and LeMay, M. (1982) Occipital bunning among later Pleistocene hominids. American Journal of Physical Anthropology. 57:27-35. •Wolpoff, M.H. (1992) “Theories of modern human origins,” in Continuity or replacement: Controversies in Homo sapiens evolution. Ed. G. Brauer & F.H. Smith, pp. 25-63.Rotterdam: A. A. Balkema. •Yaroch, L.A. (1996) Shape analysis using the thin-plate spline. American Journal of Physical Anthroplogy. 101:43-89.