Sexual Dimorphism

doi:10.1146/annurev.an.14.100185.002241Annual Review of Anthropology http://arjournals.annualreviews.org/loi/anthr

A comparison of sexual dimorphism and range of variation in Papio cynocephalus and Gorilla gorilla dentition

The dentitions of 48 baboons ( Papio cynocephalus ) and 242 gorillas ( Gorilla gorilla ) are compared metrically and the baboons are found to have a greater range of variation, and greater sexual dimorphism than the gorillas. This is explained in terms of the different ecologies of these species: life on the African savannah, with its sharp seasonal changes in available food, seems to have given selective advantage to broader niches than life in the rain forest. Further, the historic continuity of the savannah has provided fewer chances for allopatric speciation than the rain forest. These contrasts between forest and savannah speciation should provide insights into hominid evolution. In trying to judge whether australopithecines, probable savannah residents, can be lumped into one or several species, based upon dental variability, a comparison with baboons should be more informative than the now frequently used contrast with gorillas.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41597/1/10329_2006_Article_BF02381794.pd

Sixty Years of Modern Human Origins in the American Anthropological Association

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65197/1/aa.2003.105.1.89.pd

Mitochondrial diversity within modern human populations

With the recent increase in the available number of high-quality, full-length mitochondrial sequences, it is now possible to construct and analyze a comprehensive human mitochondrial consensus sequence. Using a data set of 827 carefully selected sequences, it is shown that modern humans contain extremely low levels of divergence from the mitochondrial consensus sequence, differing by a mere 21.6 nt sites on average. Fully 84.1% of the mitochondrial genome was found to be invariant and ‘private’ mutations accounted for 43.8% of the variable sites. Ninety eight percent of the variant sites had a primary nucleotide with an allele frequency of 0.90 or greater. Interestingly, the few truly ambiguous nucleotide sites could all be reliably assigned to either a purine or pyrimidine ancestral state. A comparison of this consensus sequence to several ancestral sequences derived from phylogenetic studies reveals a great deal of similarity, where, as expected, the most phylogenetically informative nucleotides in the ancestral studies tended to be the most variable nucleotides in the consensus. Allowing for this fact, the consensus approach provides variation data on the positions that do not contribute to phylogenetic reconstructions, and these data provide a baseline for measuring human mitochondrial variation in populations worldwide

Hybridization in human evolution: Insights from other organisms

During the late Pleistocene, isolated lineages of hominins exchanged genes thus influencing genomic variation in humans in both the past and present. However, the dynamics of this genetic exchange and associated phenotypic consequences through time remain poorly understood. Gene exchange across divergent lineages can result in myriad outcomes arising from these dynamics and the environmental conditions under which it occurs. Here we draw from our collective research across various organisms, illustrating some of the ways in which gene exchange can structure genomic/phenotypic diversity within/among species. We present a range of examples relevant to questions about the evolution of hominins. These examples are not meant to be exhaustive, but rather illustrative of the diverse evolutionary causes/consequences of hybridization, highlighting potential drivers of human evolution in the context of hybridization including: influences on adaptive evolution, climate change, developmental systems, sex-differences in behavior, Haldane’s rule and the large X-effect, and transgressive phenotypic variation.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151330/1/evan21787.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151330/2/evan21787_am.pd

The Stem Species of Our Species: A Place for the Archaic Human Cranium from Ceprano, Italy

One of the present challenges in the study of human evolution is to recognize the hominin taxon that was ancestral to Homo sapiens. Some researchers regard H. heidelbergensis as the stem species involved in the evolutionary divergence leading to the emergence of H. sapiens in Africa, and to the evolution of the Neandertals in Europe. Nevertheless, the diagnosis and hypodigm of H. heidelbergensis still remain to be clarified. Here we evaluate the morphology of the incomplete cranium (calvarium) known as Ceprano whose age has been recently revised to the mid of the Middle Pleistocene, so as to test whether this specimen may be included in H. heidelbergensis. The analyses were performed according to a phenetic routine including geometric morphometrics and the evaluation of diagnostic discrete traits. The results strongly support the uniqueness of H. heidelbergensis on a wide geographical horizon, including both Eurasia and Africa. In this framework, the Ceprano calvarium – with its peculiar combination of archaic and derived traits – may represent, better than other penecontemporaneous specimens, an appropriate ancestral stock of this species, preceding the appearance of regional autapomorphic features

High mutation rates explain low population genetic divergence at copy-number-variable loci in Homo sapiens

Copy-number-variable (CNV) loci differ from single nucleotide polymorphic (SNP) sites in size, mutation rate, and mechanisms of maintenance in natural populations. It is therefore hypothesized that population genetic divergence at CNV loci will differ from that found at SNP sites. Here, we test this hypothesis by analysing 856 CNV loci from the genomes of 1184 healthy individuals from 11 HapMap populations with a wide range of ancestry. The results show that population genetic divergence at the CNV loci is generally more than three times lower than at genome-wide SNP sites. Populations generally exhibit very small genetic divergence (G(st) = 0.05 ± 0.049). The smallest divergence is among African populations (G(st) = 0.0081 ± 0.0025), with increased divergence among non-African populations (G(st) = 0.0217 ± 0.0109) and then among African and non-African populations (G(st) = 0.0324 ± 0.0064). Genetic diversity is high in African populations (~0.13), low in Asian populations (~0.11), and intermediate in the remaining 11 populations. Few significant linkage disequilibria (LDs) occur between the genome-wide CNV loci. Patterns of gametic and zygotic LDs indicate the absence of epistasis among CNV loci. Mutation rate is about twice as large as the migration rate in the non-African populations, suggesting that the high mutation rates play dominant roles in producing the low population genetic divergence at CNV loci

Homeotic Evolution in the Mammalia: Diversification of Therian Axial Seriation and the Morphogenetic Basis of Human Origins

Despite the rising interest in homeotic genes, little has been known about the course and pattern of evolution of homeotic traits across the mammalian radiation. An array of emerging and diversifying homeotic gradients revealed by this study appear to generate new body plans and drive evolution at a large scale.This study identifies and evaluates a set of homeotic gradients across 250 extant and fossil mammalian species and their antecedents over a period of 220 million years. These traits are generally expressed as co-linear gradients along the body axis rather than as distinct segmental identities. Relative position or occurrence sequence vary independently and are subject to polarity reversal and mirroring. Five major gradient modification sets are identified: (1)--quantitative changes of primary segmental identity pattern that appeared at the origin of the tetrapods ; (2)--frame shift relation of costal and vertebral identity which diversifies from the time of amniote origins; (3)--duplication, mirroring, splitting and diversification of the neomorphic laminar process first commencing at the dawn of mammals; (4)--emergence of homologically variable lumbar lateral processes upon commencement of the radiation of therian mammals and ; (5)--inflexions and transpositions of the relative position of the horizontal septum of the body and the neuraxis at the emergence of various orders of therian mammals. Convergent functional changes under homeotic control include laminar articular engagement with septo-neural transposition and ventrally arrayed lumbar transverse process support systems.Clusters of homeotic transformations mark the emergence point of mammals in the Triassic and the radiation of therians in the Cretaceous. A cluster of homeotic changes in the Miocene hominoid Morotopithecus that are still seen in humans supports establishment of a new "hominiform" clade and suggests a homeotic origin for the human upright body plan

Two interpretations of human evolution: Essentialism and Darwinism

Despite intensive studies of a large number of fossils discovered during the 20th century there is no consensus as to the interpretation of the process of hominin evolution. Some authors see as many as six genera and some 17 species, while others argue for a single lineage from Plio/Pleistocene until today. Such diversity of interpretations of the same facts indicates lack of a uniform theoretical basis underlying studies of human evolution. Debates can be resolved using basic principles of scientific inquiry - parsimony and falsification of null hypotheses. Hypothesis testing is now possible with respect to the evolution of basic hominin characteristics such as brain size, body size and the size of the dentition that have sample sizes of a few hundred individual data points each. These characters display a continuous change with time. Analyses of variance do not falsify the null hypothesis of the existence of only one species at any time - variances around regression lines on time do not differ from the variance observed in the single species of Homo sapiens - distributions of residuals are normal. Thus, splitting of the hominin lineage into coeval species can only be based on descriptive characteristics that are liable to errors of subjective judgment.Maciej Henneber