Detecting genetic drift versus selection in human evolution

Ackermann, Rebecca Rogers; Cheverud, James M.

doi:10.1073/pnas.0405919102

Cited by 183 publications

(192 citation statements)

References 38 publications

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“…However, many aspects of brain reorganization are not captured by those endocranial metrics, particularly those related to finer-grained organization such as sulcal variation, brain asymmetries, and volumetric changes of certain areas, among others. The predominant role of neutral mechanisms in the evolution of endocranial shape is consistent with previously published work reporting a major role of genetic drift in craniofacial evolution during the AustralopithecusHomo transition (35,36) and during the divergence of Neanderthals and modern humans (37). Although our study focuses on endocranial variation, our findings are consistent with a general neutral scenario for the evolution of craniofacial shape in hominins.…”

Section: Discussionsupporting

confidence: 82%

Brain enlargement and dental reduction were not linked in hominin evolution

Gómez‐Robles

Smaers

Holloway

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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The large brain and small postcanine teeth of modern humans are among our most distinctive features, and trends in their evolution are well studied within the hominin clade. Classic accounts hypothesize that larger brains and smaller teeth coevolved because behavioral changes associated with increased brain size allowed a subsequent dental reduction. However, recent studies have found mismatches between trends in brain enlargement and posterior tooth size reduction in some hominin species. We use a multiple-variance Brownian motion approach in association with evolutionary simulations to measure the tempo and mode of the evolution of endocranial and dental size and shape within the hominin clade. We show that hominin postcanine teeth have evolved at a relatively consistent neutral rate, whereas brain size evolved at comparatively more heterogeneous rates that cannot be explained by a neutral model, with rapid pulses in the branches leading to later Homo species. Brain reorganization shows evidence of elevated rates only much later in hominin evolution, suggesting that fast-evolving traits such as the acquisition of a globular shape may be the result of direct or indirect selection for functional or structural traits typical of modern humans.endocast | postcanine teeth | evolutionary rates | selection | paleoanthropology I n comparison with other hominins, modern humans are characterized by their large brain and small posterior teeth. These traits are among our most distinctive features, and trends in their evolution are well studied because of the phylogenetic and functional implications of variation in dental and cerebral anatomy (1-3). Brain expansion and postcanine reduction appear to follow parallel trends during hominin evolution, and classic views consider that an increase in brain size was linked to more complex behavior that included the manufacture and use of stone tools, which allowed a subsequent dental reduction. A shift toward a higher-quality diet during the evolution of early Homo also has been related to brain size increase and posterior tooth reduction (4, 5). However, it has been suggested recently that brain expansion in early Homo, as inferred from endocranial volume, substantially preceded dental reduction (6). It also has been noted that early in the Neanderthal lineage strong dental reduction preceded the additional brain expansion seen in the later "classic" Neanderthals (7). The suggestion that stone tool use and manufacture substantially predated the increase in brain size observed in early Homo (8) adds further complexity to this scenario.Recent developments in ancestral state reconstruction (9, 10) allow lineage-specific patterns of brain expansion and dental reduction to be quantified and compared. Unlike traditional approaches to ancestral state reconstruction that assume a neutral evolutionary scenario, which is likely unrealistic in most cases, we used a variable rate approach that estimates differences in evolutionary rates across different branches of a given phylogeny. We appli...

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Section: Discussionsupporting

confidence: 82%

Brain enlargement and dental reduction were not linked in hominin evolution

Gómez‐Robles

Smaers

Holloway

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…Depending on the particular hypothesis, different approaches can be taken to assess consistency, but biomechanical modeling or laboratory experiments are often used (31). Third, it is sometimes possible to distinguish among different evolutionary explanations by explicitly modeling evolutionary forces with quantitative and population genetics (18,32). This modeling can be used to evaluate the importance of genetic drift vs. natural selection or the fit of different selective hypotheses with observed data.…”

Section: Single Features Vs Complexes Of Featuresmentioning

confidence: 99%

The meaning of Neandertal skeletal morphology

Weaver

2009

Proc. Natl. Acad. Sci. U.S.A.

125

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A procedure is outlined for distinguishing among competing hypotheses for fossil morphology and then used to evaluate current views on the meaning of Neandertal skeletal morphology. Three explanations have dominated debates about the meaning of Neandertal cranial features: climatic adaptation, anterior dental loading, and genetic drift. Neither climatic adaptation nor anterior dental loading are well supported, but genetic drift is consistent with the available evidence. Climatic adaptation and activity patterns are the most discussed explanations for Neandertal postcranial features. Robust empirical relationships between climate and body form in extant humans and other endotherms currently make climatic adaptation the most plausible explanation for the wide bodies and relatively short limbs of Neandertals, and many additional postcranial features are likely secondary consequences of these overall skeletal proportions. Activity patterns may explain certain Neandertal postcranial features, but unlike the situation for climate, relationships in extant humans between morphology and activities are typically not well established. For both the cranium and the postcranium, changes in diet or activity patterns may underlie why Neandertals and Pleistocene modern humans tend to be more robust than Holocene humans.cranium ͉ human evolution ͉ modern human origins ͉ postcranium

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“…The regression vector describing the evolutionary allometry was estimated from the OLS analysis of the consensus shape coordinates on the centroid size of each sample, while the vector describing the ontogenetic allometry was estimated using a pooled within-group regression of the four ontogenetic series (Pa, PG, ChV, SP-TF). Here we assumed that these four samples were representative of the range of variation among southern South American populations because they included the range of morphological and ecological variation in the region of study (see Ackermann and Cheverud, 2004 for a similar approach). The sample used to estimate the pooled within-group ontogenetic allometry included 55 subadults from 4 to 15 years old (Table 2) and 77 adults from the same four samples.…”

Section: Comparison Of Evolutionary and Ontogenetic Allometriesmentioning

confidence: 99%

Ontogenetic Allometry and Cranial Shape Diversification Among Human Populations From South America

González

Pérez

Bernal

2011

The Anatomical Record

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Modifications of ontogenetic allometries play an important role in patterning the shape differentiation among populations. This study evaluates the influence of size variation on craniofacial shape disparity among human populations from South America and assesses whether the morphological disparity observed at the interpopulation level resulted from a variable extension of the same ontogenetic allometry, or whether it arose as a result of divergences in the pattern of size-related shape changes. The size and shape of 282 adult and subadult crania were described by geometric morphometric-based techniques. Multivariate regressions were used to evaluate the influence of size on shape differentiation between and within populations, and phylogenetic comparative methods were used to take into account the shared evolutionary history among populations. The phylogenetic generalized least-squares models showed that size accounts for a significant amount of shape variation among populations for the vault and face but not for the base, suggesting that the three modules did not exhibit a uniform response to changes in overall growth. The common slope test indicated that patterns of evolutionary and ontogenetic allometry for the vault and face were similar and characterized by a heightening of the face and a lengthening of the vault with increasing size. The conservation of the same pattern of shape changes with size suggests that differences in the extent of growth contributed to the interpopulation cranial shape variation and that certain directions of morphological change were favored by the trait covariation along ontogeny. Anat Rec, 294:1864Rec, 294: -1874Rec, 294: , 2011. V V C 2011 Wiley-Liss, Inc.

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Detecting genetic drift versus selection in human evolution

Cited by 183 publications

References 38 publications

Brain enlargement and dental reduction were not linked in hominin evolution

Brain enlargement and dental reduction were not linked in hominin evolution

The meaning of Neandertal skeletal morphology

Ontogenetic Allometry and Cranial Shape Diversification Among Human Populations From South America

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