Fine-scaled climate variation in equatorial Africa revealed by modern and fossil primate teeth.

Variability in resource availability is hypothesized to be a significant driver of primate adaptation and evolution, but most paleoclimate proxies cannot recover environmental seasonality on the scale of an individual lifespan. Oxygen isotope compositions (δ18O values) sampled at high spatial resolution in the dentitions of modern African primates (n = 2,352 near weekly measurements from 26 teeth) track concurrent seasonal precipitation, regional climatic patterns, discrete meteorological events, and niche partitioning. We leverage these data to contextualize the first δ18O values of two 17 Ma Afropithecus turkanensis individuals from Kalodirr, Kenya, from which we infer variably bimodal wet seasons, supported by rainfall reconstructions in a global Earth system model. Afropithecus' δ18O fluctuations are intermediate in magnitude between those measured at high resolution in baboons (Papio spp.) living across a gradient of aridity and modern forest-dwelling chimpanzees (Pan troglodytes verus). This large-bodied Miocene ape consumed seasonally variable food and water sources enriched in 18O compared to contemporaneous terrestrial fauna (n = 66 fossil specimens). Reliance on fallback foods during documented dry seasons potentially contributed to novel dental features long considered adaptations to hard-object feeding. Developmentally informed microsampling recovers greater ecological complexity than conventional isotope sampling; the two Miocene apes (n = 248 near weekly measurements) evince as great a range of seasonal δ18O variation as more time-averaged bulk measurements from 101 eastern African Plio-Pleistocene hominins and 42 papionins spanning 4 million y. These results reveal unprecedented environmental histories in primate teeth and suggest a framework for evaluating climate change and primate paleoecology throughout the Cenozoic.

The anatomy of the hindlimb of Theropithecus brumpti (Cercopithecidae, Papionini): Morphofunctional implications.

Theropithecus brumpti is a primate known from numerous craniodental specimens in the Plio-Pleistocene Shungura Formation (Lower Omo Valley, Ethiopia), but the anatomy of its hindlimb is documented only by a few associated and mostly incomplete postcranial specimens. The adaptations of T. brumpti are still debated, with its substrate preferences and its use of squatting postures recently discussed based on anatomical differences when compared with its extant representative, Theropithecus gelada. Here, we describe an associated femur and tibia (L 869-1 and L 869-2) of a presumed T. brumpti male and a partial foot (L 865-1r and L 865-1t) of a male T. brumpti, dated to ca. 2.6 Ma and ca. 2.32 Ma respectively. Based on univariate and bivariate morphometric analyses, we provide new data on the morphological correlates of substrate preferences and postural behaviors of this fossil species. Our results are in agreement with previous analyses and present T. brumpti as a predominantly terrestrial primate. We demonstrate the presence of osteological correlates associated with the use of squatting behaviors in T. brumpti but also point to significant anatomical differences between this paleontological species and T. gelada. These differences blur the functional value of characters previously identified as diagnostic of T. gelada and its postural behavior. We further document the postcranial distinctiveness of the Theropithecus clade in relation to the Papio clade. This study thus provides new insights into the postcranial anatomy and paleoecology of an abundant fossil primate from the Plio-Pleistocene of eastern Africa.

Enamel chipping and its ecological correlates in African papionins: Implications for hominin feeding behavior.

African papionins are classic paleoecological referents for fossil hominins. Enamel chips on the teeth of baboons and hominins are argued to represent responses to similar dietary habits; however, a comprehensive analysis of modern papionin chipping is lacking, leaving open the question of analog suitability. Here, we investigate patterns of antemortem enamel chipping across a diverse set of African papionin species occupying a range of ecological niches. We compare papionin chipping frequencies to estimates for Plio-Pleistocene hominins to address hypotheses of habitat and/or dietary similarities. Antemortem chips in seven African papionin species were scored on intact postcanine teeth (P3-M3) using established protocols. Chip size was scored on a tripartite scale. Papio hamadryas and Papio ursinus-two common paleoecological referents-display higher levels of chipping than Plio-Pleistocene hominin taxa (Australopithecus and Paranthropus) posited to have similar dietary habits. Papio populations occupying dry or highly seasonal habitats accumulate more large chips than Papio taxa occupying more mesic habitats, and terrestrial papionins chip their teeth more often than closely related taxa occupying arboreal niches. Chipping is present on the teeth of all Plio-Pleistocene hominins; however, chipping in baboons (P. ursinus and P. hamadryas) consistently exceeds most hominin taxa. Chipping frequencies on their own do not reliably sort taxa into major dietary groupings. We conclude that the large differences in chipping frequency may instead reflect habitat use and food processing idiosyncrasies. Less chipping in Plio-Pleistocene hominin teeth compared to modern Papio is more likely attributable to differences in dental morphology rather than diet.

Differences among the forelimb arteries in groups of primates and a mathematical model explanation.

BACKGROUND: Recently, some studies about primates have claimed the importance of the vessels to maintain the muscles working; in fact, the arterial supply could suggest how strenuous the muscular performance is associated to locomotor behavior. The aim of this work was to study the anatomy of the arteries of the forelimbs of different groups of primates to evidence a general arterial model in comparative terms. METHODS: We propose a biophysical explanation for the arterial pattern of the forelimbs of primates' groups. RESULTS: Three pattern of the forelimb arteries in Primates were descript and the differences were explained using mathematical formulas. CONCLUSIONS: The anatomical study about the comparative anatomy of the arteries of the forelimbs of primates provided hypothesis about the three observed models, mainly in relation to brachial artery division and the number of the palmar arches, in mathematical models' terms.

Baboon biogeography, divergence, and evolution: Morphological and paleoecological perspectives.

Papio originated in the early Pleistocene and diverged into multiple species, six of which are extant. Among parapatric Papio species, there are obvious phenotypic differences that arose during the radiation of the genus. We use data from modern baboon ecology and morphology, as well as fossils and paleoecology, to examine baboon biogeography, divergence, and evolution, focusing on skull form and body mass. To provide context, techniques of historical biogeography, combining data from modern distributions in statistical models alongside qualitative assessments of the fossil record, were used to estimate ancestral ranges in papionins. The ancestral range of Papio was estimated to be in South Tropical Africa rather than in the far south of the continent, followed by multiple movements south and west. Progress to the north and east may have been slowed because of high-density blocking of niches by other monkeys. Geometric morphometric data were used in partial least squares analysis with dietary, environmental, and other variables to investigate skull differentiation. Environment was significantly correlated with skull form, but diet emerged as more significant. Exploitation of subterranean foods was found to be an important influence on skull morphology. Bayesian modeling of cercopithecid body mass data allowed reconstruction of ancestral body mass and showed a pattern of accelerating body mass evolution in a number of lineages. This appears to be related to exploitation of terrestrial niches in the Pliocene, with terrestriality also implicated in the large geographic distributions of many fossil and modern papionins, including Papio. Given the greater heterogeneity of body masses in males, size differentiation within Papio seems most likely to be linked to sexual selection rather than environmental factors, although further work is required to examine the relative importance of plasticity versus local adaptation in shaping baboon phenotypic variation.

Allometry and advancing age significantly structure craniofacial variation in adult female baboons.

Primate craniofacial growth is traditionally assumed to cease upon maturation or at least be negligible, whereas bony remodeling is typically associated with advanced adult age and, in particular, tooth loss. Therefore, size and shape of the craniofacial skeleton of young and middle-aged adults should be stable. However, research on both modern and historic human samples suggests that portions of the CFS exhibit age-related changes in mature individuals, both related to and independent of tooth loss. These results demonstrate that the age-category 'adult' is heterogeneous, containing individuals demonstrating post-maturational age-related variation, but the topic remains understudied outside of humans and in the cranial vault and base. Our research quantifies variation in a sample of captive adult female baboons (n = 97) in an effort to understand how advancing age alters the mature CFS. Craniometric landmarks and sliding semilandmarks were collected from computed tomography (CT) scans of adult baboons aged 7-32 years old. To determine whether craniofacial morphology is sensitive to aging mechanisms and whether any such effects are differentially distributed throughout the cranium, geometric morphometric techniques were employed to compare the shapes of various cranial regions among individuals of increasing age. Unexpectedly, the biggest form differences were observed between young and middle-aged adults, rather than between adults with full dentitions and those with some degree of tooth loss. Shape variation was greatest in masticatory and nuchal musculature attachment areas. Our results indicate that the craniofacial skeleton changes form during adulthood in baboons, raising interesting questions about the molecular and biological mechanisms governing these changes.

Sexual selection in the Kinda baboon.

Due to wide variation in the presence and degree of expression of a diverse suite of sexually-selected traits, the tribe Papionini represents an outstanding model for understanding how variation in sexual selection pressures and mechanisms leads to trait evolution. Here, we discuss the particular value of Papio as a model genus for studies of sexual selection, emphasizing the presence of multiple mating systems, and differences in the expression of sexually-selected traits among closely-related species. We draw particular attention to the Kinda baboon (Papio kindae), a comparatively less-studied baboon species, by providing a primer to Kinda baboon morphology, genetics, physiology, and behavior. Based on observations of large group sizes, combined with low degrees of sexual dimorphism and large relative testis size relative to other baboon species, we test the hypothesis that Kinda baboons have evolved under reduced direct, and increased indirect, male-male competition. We present the first long-term data on wild Kinda baboons in Zambia. Kinda baboon females show seasonal peaks in births and reproductive receptivity, and males exhibit a queing-rather than contest-based dominance acquisition with long alpha-male tenure lengths. We finish by making a number of explicit testable predictions about Kinda baboon sexual signals and behaviors, and suggest that Kinda baboons have potential to offer new insights into the selective environments that may have been experienced during homininization.

Additive genetic variation in the craniofacial skeleton of baboons (genus Papio) and its relationship to body and cranial size.

OBJECTIVES: Determining the genetic architecture of quantitative traits and genetic correlations among them is important for understanding morphological evolution patterns. We address two questions regarding papionin evolution: (1) what effect do body and cranial size, age, and sex have on phenotypic (VP ) and additive genetic (VA ) variation in baboon crania, and (2) how might additive genetic correlations between craniofacial traits and body mass affect morphological evolution? MATERIALS AND METHODS: We use a large captive pedigreed baboon sample to estimate quantitative genetic parameters for craniofacial dimensions (EIDs). Our models include nested combinations of the covariates listed above. We also simulate the correlated response of a given EID due to selection on body mass alone. RESULTS: Covariates account for 1.2-91% of craniofacial VP . EID VA decreases across models as more covariates are included. The median genetic correlation estimate between each EID and body mass is 0.33. Analysis of the multivariate response to selection reveals that observed patterns of craniofacial variation in extant baboons cannot be attributed solely to correlated response to selection on body mass, particularly in males. DISCUSSION: Because a relatively large proportion of EID VA is shared with body mass variation, different methods of correcting for allometry by statistically controlling for size can alter residual VP patterns. This may conflate direct selection effects on craniofacial variation with those resulting from a correlated response to body mass selection. This shared genetic variation may partially explain how selection for increased body mass in two different papionin lineages produced remarkably similar craniofacial phenotypes.

The average baboon brain: MRI templates and tissue probability maps from 89 individuals.

The baboon (Papio) brain is a remarkable model for investigating the brain. The current work aimed at creating a population-average baboon (Papio anubis) brain template and its left/right hemisphere symmetric version from a large sample of T1-weighted magnetic resonance images collected from 89 individuals. Averaging the prior probability maps output during the segmentation of each individual also produced the first baboon brain tissue probability maps for gray matter, white matter and cerebrospinal fluid. The templates and the tissue probability maps were created using state-of-the-art, freely available software tools and are being made freely and publicly available: http://www.nitrc.org/projects/haiko89/ or http://lpc.univ-amu.fr/spip.php?article589. It is hoped that these images will aid neuroimaging research of the baboon by, for example, providing a modern, high quality normalization target and accompanying standardized coordinate system as well as probabilistic priors that can be used during tissue segmentation.

Variation in the nasal cavity of baboon hybrids with implications for late Pleistocene hominins.

Hybridization is increasingly proving to be an important force shaping human evolution. Comparisons of both ancient and modern genomes have provided support for a complex evolutionary scenario over the past million years, with evidence for multiple incidents of gene exchange. However, to date, genetic evidence is still limited in its ability to pinpoint the precise time and place of ancient admixture. For that we must rely on evidence of admixture from the skeleton. The research presented here builds on previous work on the crania of baboon hybrids, focusing on the nasal cavity of olive baboons, yellow baboons, and first generation (F1) hybrids. The nasal cavity is a particularly important anatomical region for study, given the clear differentiation of this feature in Neanderthals relative to their contemporaries, and therefore it is a feature that will likely differ in a distinctive manner in hybrids of these taxa. Metric data consist of 45 linear, area, and volume measurements taken from CT scans of known-pedigree baboon crania. Results indicate that there is clear evidence for differences among the nasal cavities of the parental taxa and their F1 hybrids, including a greater degree of sexual dimorphism in the hybrids. There is also some evidence for transgressive phenotypes in individual F1 animals. The greatest amount of shape variation occurs in the anterior bony cavity, the choana, and the mid-nasopharynx. Extrapolating our results to the fossil record, we would expect F1 hybrid fossils to have larger nasal cavities, on average, than either parental taxon, with overall nasal cavity shape showing the most profound changes in regions that are distinct between the parental taxa (e.g., anterior nasal cavity). We also expect size and shape differences to be more pronounced in male F1 hybrids than in females. Because of pronounced anterior nasal cavity differences between Neanderthals and their contemporaries, we suggest that this model might be effective for examining the fossil record of late Pleistocene contact.

Ontogenetic scaling of fore limb and hind limb joint posture and limb bone cross-sectional geometry in vervets and baboons.

OBJECTIVES: Previous studies suggest that the postures habitually adopted by an animal influence the mechanical loading of its long bones. Relatively extended limb postures in larger animals should preferentially reduce anteroposterior (A-P) relative to mediolateral (M-L) bending of the limb bones and therefore decrease A-P/M-L rigidity. We test this hypothesis by examining growth-related changes in limb bone structure in two primate taxa that differ in ontogenetic patterns of joint posture. MATERIALS AND METHODS: Knee and elbow angles of adult and immature vervets (Chlorocebus aethiops, n = 16) were compared to published data for baboons (Papio hamadryas ursinus, n = 33, Patel et al., ). Ontogenetic changes in ratios of A-P/M-L bending rigidity in the femur and humerus were compared in skeletal samples (C. aethiops, n = 28; P. cynocephalus, n = 39). Size changes were assessed with linear regression, and age group differences tested with ANOVA. RESULTS: Only the knee of baboons shows significant postural change, becoming more extended with age and mass. A-P/M-L bending rigidity of the femur decreases during ontogeny in immature and adult female baboons only. Trends in the humerus are less marked. Adult male baboons have higher A-P/M-L bending rigidity of the femur than females. CONCLUSIONS: The hypothesized relationship between more extended joints and reduced A-P/M-L bending rigidity is supported by our results for immature and adult female baboon hind limbs, and the lack of significant age changes in either parameter in forelimbs and vervets. Adult males of both species depart from general ontogenetic trends, possibly due to socially mediated behavioral differences between sexes. Am J Phys Anthropol 161:72-83, 2016. © 2016 Wiley Periodicals, Inc.

Synaptic connections of amacrine cells containing vesicular glutamate transporter 3 in baboon retinas.

The goals of these experiments were to describe the morphology and synaptic connections of amacrine cells in the baboon retina that contain immunoreactive vesicular glutamate transporter 3 (vGluT3). These amacrine cells had the morphology characteristic of knotty bistratified type 1 cells, and their dendrites formed two plexuses on either side of the center of the inner plexiform layer. The primary dendrites received large synapses from amacrine cells, and the higher-order dendrites were both pre- and postsynaptic to other amacrine cells. Based on light microscopic immunolabeling results, these include AII cells and starburst cells, but not the polyaxonal amacrine cells tracer-coupled to ON parasol ganglion cells. The vGluT3 cells received input from ON bipolar cells at ribbon synapses and made synapses onto OFF bipolar cells, including the diffuse DB3a type. Many synapses from vGluT3 cells onto retinal ganglion cells were observed in both plexuses. At synapses where vGluT3 cells were presynaptic, two types of postsynaptic densities were observed; there were relatively thin ones characteristic of inhibitory synapses and relatively thick ones characteristic of excitatory synapses. In the light microscopic experiments with Neurobiotin-injected ganglion cells, vGluT3 cells made contacts with midget and parasol ganglion cells, including both ON and OFF types. Puncta containing immunoreactive gephyrin, an inhibitory synapse marker, were found at appositions between vGluT3 cells and each of the four types of labeled ganglion cells. The vGluT3 cells did not have detectable levels of immunoreactive γ-aminobutyric acid (GABA) or immunoreactive glycine transporter 1. Thus, the vGluT3 cells would be expected to have ON responses to light and make synapses onto neurons in both the ON and the OFF pathways. Taken with previous results, these findings suggest that vGluT3 cells release glycine at some of their output synapses and glutamate at others.

Comparative anatomy of the pelvic vessels in the bearded capuchin (Sapajus libidinosus) and baboons, apes and modern humans.

Cebus/Sapajus has shown high cognitive and manipulatory behaviour as well as intermittent bipedalism. Although the function of the muscles and bones of this genus has been widely investigated, the arterial system that supports these tissues has not been studied in much detail, and a full description of the blood vessels of the pelvis is still missing. Therefore, we studied the vessels of the pelvis of Sapajus libidinosus in terms of their origin, distribution and muscle irrigation and compared them with those of other primates available in the literature. In general, the distribution pattern and origin of arteries in the pelvis of the bearded capuchin are more similar to those of baboons compared to other primates. This similarity may be because both have a tail, a similar body shape and use, preferentially, quadrupedal movement.

New insights into patterns of integration in the femur and pelvis among catarrhines.

OBJECTIVES: Integration reflects the level of coordinated variation of the phenotype. The integration of postcranial elements can be studied from a functional perspective, especially with regards to locomotion. This study investigates the link between locomotion, femoral structural properties, and femur-pelvis complex morphology. MATERIALS AND METHODS: We measured (1) morphological integration between femoral and pelvic morphologies using geometric morphometrics, and (2) covariation between femoral/pelvic morphologies and femoral diaphyseal cross-sectional properties, which we defined as morpho-structural integration. Morphological and morpho-structural integration patterns were measured among humans (n = 19), chimpanzees and bonobos (n = 16), and baboons (n = 14), whose locomotion are distinct. RESULTS: Baboons show the highest magnitude of morphological integration and the lowest of morpho-structural integration. Chimpanzees and bonobos show intermediate magnitude of morphological and morpho-structural integration. Yet, body size seems to have a considerable influence on both integration patterns, limiting the interpretations. Finally, humans present the lowest morphological integration and the highest morpho-structural integration between femoral morphology and structural properties but not between pelvic morphology and femur. DISCUSSION: Morphological and morpho-structural integration depict distinct strategies among the samples. A strong morphological integration among baboon's femur-pelvis module might highlight evidence for long-term adaptation to quadrupedalism. In humans, it is likely that distinct selective pressures associated with the respective function of the pelvis and the femur tend to decrease morphological integration. Conversely, high mechanical loading on the hindlimbs during bipedal locomotion might result in specific combination of structural and morphological features within the femur.

Biogeographic variation in the baboon: dissecting the cline.

All species demonstrate intraspecific anatomical variation. While generalisations such as Bergman's and Allen's rules have attempted to explain the geographic structuring of variation with some success, recent work has demonstrated limited support for these in certain Old World monkeys. This study extends this research to the baboon: a species that is widely distributed across sub-Saharan Africa and exhibits clinal variation across an environmentally disparate range. This study uses trend surface analysis to map the pattern of skull variation in size and shape in order to visualise the main axes of morphological variation. Patterns of shape and size-controlled shape are compared to highlight morphological variation that is underpinned by allometry alone. Partial regression is used to dissociate the effects of environmental terms, such as rainfall, temperature and spatial position. The diminutive Kinda baboon is outlying in size, so analyses were carried out with and without this taxon. Skull size variation demonstrates an east-west pattern, with small animals at the two extremes and large animals in Central and Southern Africa. Shape variation demonstrates the same geographical pattern as skull size, with small-sized animals exhibiting classic paedomorphic morphology. However, an additional north-south axis of variation emerges. After controlling for skull size, the diminutive Kinda baboon is no longer an outlier for size and shape. Also, the east-west component is no longer evident and discriminant function analysis shows an increased misclassification of adjacent taxa previously differentiated by size. This demonstrates the east-west component of shape variation is underpinned by skull size, while the north-south axis is not. The latter axis is explicable in phylogenetic terms: baboons arose in Southern Africa and colonised East and West Africa to the north, diverging in the process, aided by climate-mediated isolating mechanisms. Environmental terms appear poorly correlated with shape variation compared with geography. This might indicate that there is no simple environment-morphology association, but certainly demonstrates that phylogenetic history is an overbearing factor in baboon morphological variation.

Genome-wide coancestry reveals details of ancient and recent male-driven reticulation in baboons.

Baboons (genus Papio) are a morphologically and behaviorally diverse clade of catarrhine monkeys that have experienced hybridization between phenotypically and genetically distinct phylogenetic species. We used high-coverage whole-genome sequences from 225 wild baboons representing 19 geographic localities to investigate population genomics and interspecies gene flow. Our analyses provide an expanded picture of evolutionary reticulation among species and reveal patterns of population structure within and among species, including differential admixture among conspecific populations. We describe the first example of a baboon population with a genetic composition that is derived from three distinct lineages. The results reveal processes, both ancient and recent, that produced the observed mismatch between phylogenetic relationships based on matrilineal, patrilineal, and biparental inheritance. We also identified several candidate genes that may contribute to species-specific phenotypes.

Fossil papio cranium from !Ncumtsa (Koanaka) Hills, western Ngamiland, Botswana.

Three fossils, a cranium of Papio, a cercopithecid frontal bone, and a mandible of juvenile Papio, have been recovered from cave deposits in the !Ncumtsa (Koanaka) Hills of western Ngamiland, Botswana. These specimens are significant because well-preserved crania of Papio are extremely rare in the fossil record outside of South Africa and because this is the first report of fossil primate cranial remains from Botswana. Thermoluminescence dating of surrounding cave matrix indicates an age of ≥317 ± 114 ka, within the Middle Pleistocene, although it may be older. Based on univariate and multivariate analyses, the adult !Ncumtsa specimen falls within the range of variation seen in extant forms of Papio, yet is distinct from any living species/subspecies and represents a new taxon, named here as a new subspecies of Papio hamadryas-Papio hamadryas botswanae.

Modularity in the mammalian dentition: mice and monkeys share a common dental genetic architecture.

The concept of modularity provides a useful tool for exploring the relationship between genotype and phenotype. Here, we use quantitative genetics to identify modularity within the mammalian dentition, connecting the genetics of organogenesis to the genetics of population-level variation for a phenotype well represented in the fossil record. We estimated the correlations between dental traits owing to the shared additive effects of genes (pleiotropy) and compared the pleiotropic relationships among homologous traits in two evolutionary distant taxa-mice and baboons. We find that in both mice and baboons, who shared a common ancestor >65 Ma, incisor size variation is genetically independent of molar size variation. Furthermore, baboon premolars show independent genetic variation from incisors, suggesting that a modular genetic architecture separates incisors from these posterior teeth as well. Such genetic independence between modules provides an explanation for the extensive diversity of incisor size variation seen throughout mammalian evolution-variation uncorrelated with equivalent levels of postcanine tooth size variation. The modularity identified here is supported by the odontogenic homeobox code proposed for the patterning of the rodent dentition. The baboon postcanine pattern of incomplete pleiotropy is also consistent with predictions from the morphogenetic field model.

Kinda baboons (Papio kindae) and grayfoot chacma baboons (P. ursinus griseipes) hybridize in the Kafue river valley, Zambia.

The ranges of small kinda (Papio kindae) and much larger grayfooted chacma (P. ursinus griseipes) baboons adjoin in the Kafue National Park, Zambia. In a visual survey of baboons at 48 sites in the Kafue River drainage we found that, contrary to previous reports, groups at the species interface near the town of Ngoma are phenotypically diverse and presumably formed by multigenerational hybridization. Mitochondrial and/or Y-chromosome genetic markers from fecal samples (N=164) collected at 29 sites support this conclusion. Groups with phenotypic signs of a history of hybridization also had taxon-specific mitochondria and Y-haplotypes from both parental species. Although the distribution of mitochondrial haplotypes largely mirrored that of external phenotypes, a significant proportion of male specimens from grayfoot as well as hybrid groups carried kinda Y-chromosomes, and kinda Y-chromosomes were involved in all observed cases of mitochondrial/Y-chromosome discordance. These observations are consistent with, though they do not prove, a population history in which the range of chacmas and the hybrid zone have advanced at the expense of the kinda range. They also suggest that, unexpectedly, kinda male×chacma female matings are much more common than the reciprocal cross in the ancestry of hybrids. We suggest that distinctive male kinda behavior and the "juvenile" appearance of kinda baboons of both sexes, perhaps combined with obstetric difficulties of a small kinda female carrying the large offspring of a chacma male, may account for this bias.

Genetics of primary cerebral gyrification: Heritability of length, depth and area of primary sulci in an extended pedigree of Papio baboons.

Genetic control over morphological variability of primary sulci and gyri is of great interest in the evolutionary, developmental and clinical neurosciences. Primary structures emerge early in development and their morphology is thought to be related to neuronal differentiation, development of functional connections and cortical lateralization. We measured the proportional contributions of genetics and environment to regional variability, testing two theories regarding regional modulation of genetic influences by ontogenic and phenotypic factors. Our measures were surface area, and average length and depth of eleven primary cortical sulci from high-resolution MR images in 180 pedigreed baboons. Average heritability values for sulcal area, depth and length (h(2)(Area)=.38+/-.22; h(2)(Depth)=.42+/-.23; h(2)(Length)=.34+/-.22) indicated that regional cortical anatomy is under genetic control. The regional pattern of genetic contributions was complex and, contrary to previously proposed theories, did not depend upon sulcal depth, or upon the sequence in which structures appear during development. Our results imply that heritability of sulcal phenotypes may be regionally modulated by arcuate U-fiber systems. However, further research is necessary to unravel the complexity of genetic contributions to cortical morphology.