Brain Size, Cranial Morphology, Climate, and Time Machines [and Comments and Reply]

Beals, Kenneth L.; Smith, Courtland L.; Dodd, Stephen M.

doi:10.1086/203138

Cited by 300 publications

(203 citation statements)

References 40 publications

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“…Interestingly, the latitudinal gradient in human brain volume is qualitatively consistent with the trend toward higher metabolic rates with latitude in endotherms (Anderson & Jetz 2005;Beals et al 1984). And across time, one might expect changes brain size during the transition from water to land or the evolution of endothermy as these events involved changes in species' temperatures and aerobic capacity (Bennett & Ruben 1979).…”

Section: Discussionsupporting

confidence: 54%

Hotter is Smarter: The temperature-dependence of brain size in vertebrates

Gillooly

2013

Preprint

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View the peer-reviewed version (peerj.com/articles/301), which is the preferred citable publication unless you specifically need to cite this preprint. Hotter is Smarter: The temperature-dependence of brain size in vertebratesThe tremendous variation in brain size among vertebrates has long been thought to be related to differences in species' metabolic rates. Species with higher metabolic rates can supply more energy to support the relatively high cost of brain tissue. And yet, while body temperature is known to be a major determinant of metabolic rate, the possible effects of temperature on brain size have scarcely been explored. Thus, here I explore the effects of temperature on brain size among diverse vertebrates (fishes,amphibians, reptiles, birds and mammals). I find that, after controlling for body size,brain size increases exponentially with temperature in much the same way asmetabolic rate. These results suggest that temperature-dependent changes inaerobic capacity, which have long been known to affect physical performance, similarly affect brain size. The observed temperature-dependence of brain size may explain observed gradients in brain size among both ectotherms and endotherms across broad spatial and temporal scales.PeerJ PrePrints | https://peerj.com/preprints/155v1/ | v1

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Section: Discussionsupporting

confidence: 54%

Hotter is Smarter: The temperature-dependence of brain size in vertebrates

Gillooly

2013

Preprint

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“…These differences can be interpreted again as distinct pathways toward wider braincases, which would be advantageous for populations in extremely cold climates under the assumption of Bergman's and Allen's rules (Beals et al, 1983(Beals et al, , 1984: By increasing neurocranium breadth, globularity of the braincase is increased and the ratio surface/volume reduced, thus reducing heat loss through the surface of the skull. These changes toward a wider skull could be related to changes in basicranial morphology, which seems to be influencing vault morphology (Lieberman et al, 2000), as well as to the increase of general brain size (Beals et al, 1984). However, the lack of basicranial measurements in our dataset limits at this moment our capacity to further explore these hypotheses.…”

Section: Discussionmentioning

confidence: 99%

Climate Signatures in the Morphological Differentiation of Worldwide Modern Human Populations

Hübbe

Hanihara

Harvati

2009

The Anatomical Record

180

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The ability of cranial morphology to reflect population/phylogenetic history, and the degree to which it might be influenced by environmental factors and selection pressures have been widely discussed. Recent consensus views cranial morphology as largely indicative of population history in humans, with some anatomical cranial regions/measurements being more informative on population history, while others being under selection pressure. We test earlier findings using the largest and most diverse cranial dataset available as yet: 7,423 male specimens from 135 geographic human population samples represented by 33 standard craniometric linear measurements. We calculated Mahalanobis D 2 for three datasets: complete cranial dataset; facial measurement dataset; and neurocranial measurement dataset; these morphological distance matrices were then compared to matrices of geographic distances as well as of several climatic variables. Additionally, we calculated Fst values for our cranial measurements and compared the results to the expected Fst values for neutral genetic loci. Our findings support the hypothesis that cranial, and especially neurocranial morphology, is phylogenetically informative, and that aspects of the face and cranium are subject to selection related to climatic factors. The Fst analysis suggest that selection to climate is largely restricted to groups living in extremely cold environments, including Northeast Asia, North America, and Northern Europe, though each of these regions appears to have arrived at their morphology through distinct adaptive pathways. Anat Rec, 292:1720Rec, 292: -1733Rec, 292: , 2009. Key words: Fst; craniometrics; adaptation; population history; human variation; NeanderthalsThe degree to which human cranial morphology reflects population history or adaptive and developmental changes related to environmental conditions is the subject of ongoing scientific discussion in anthropology. Our understanding of the evolutionary processes affecting morphological variation directly impacts both the study of modern human geographic diversity as well as the interpretation of the human fossil record. The relevance of cranial morphology to phylogenetic reconstruction has been questioned in the past (see e.g., Collard and Wood, 2000), and convergence, parallelism, reversals, and environmen-

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“…In modern human pygmies, for example, cranial capacity is not greatly different from that in populations of larger body size. Falk et al (2005a) note that human pygmy skulls typically have cranial capacities exceeding 1,000 cc (compared to a worldwide mean value for all modern humans of 1,349 cc) (Beals et al, 1984). The adult female pygmy skull used in their comparison in fact had a cranial capacity of 1,249 cc, while modern Rampasasa pygmies on Flores have an average cranial capacity of 1,270 cc (Jacob et al, 2006), similar to the value of 1,204 cc reported by Jacob (1967) for the Flores ''pygmoid'' described by Verhoeven (1958).…”

Section: Cranial Capacitymentioning

confidence: 99%

Flores hominid: New species or microcephalic dwarf?

et al. 2006

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The proposed new hominid ''Homo floresiensis'' is based on specimens from cave deposits on the Indonesian island Flores. The primary evidence, dated at $ 18,000 y, is a skull and partial skeleton of a very small but dentally adult individual (LB1). Incomplete specimens are attributed to eight additional individuals. Stone tools at the site are also attributed to H. floresiensis. The discoverers interpreted H. floresiensis as an insular dwarf derived from Homo erectus, but others see LB1 as a small-bodied microcephalic Homo sapiens. Study of virtual endocasts, including LB1 and a European microcephalic, purportedly excluded microcephaly, but reconsideration reveals several problems. The cranial capacity of LB1 ($ 400 cc) is smaller than in any other known hominid < 3.5 Ma and is far too small to derive from Homo erectus by normal dwarfing. By contrast, some associated tools were generated with a prepared-core technique previously unknown for H. erectus, including bladelets otherwise associated exclusively with H. sapiens. The single European microcephalic skull used in comparing virtual endocasts was particularly unsuitable. The specimen was a cast, not the original skull (traced to Stuttgart), from a 10-year-old child with massive pathology. Moreover, the calotte does not fit well with the rest of the cast, probably being a later addition of unknown history. Consideration of various forms of human microcephaly and of two adult specimens indicates that LB1 could well be a microcephalic Homo sapiens. This is the most likely explanation for the incongruous association of a small-brained recent hominid with advanced stone tools.

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Brain Size, Cranial Morphology, Climate, and Time Machines [and Comments and Reply]

Cited by 300 publications

References 40 publications

Hotter is Smarter: The temperature-dependence of brain size in vertebrates

Hotter is Smarter: The temperature-dependence of brain size in vertebrates

Climate Signatures in the Morphological Differentiation of Worldwide Modern Human Populations

Flores hominid: New species or microcephalic dwarf?

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