Wing serial homologs and the origin and evolution of the insect wing

The origin and evolution of insect wings has been the subject of extensive debate. The issue has remained controversial largely because of the absence of definitive fossil evidence or direct developmental evidence of homology between wings and a putative wing origin. Recent identification of wing serial homologs (WSHs) has provided researchers with a potential strategy for identifying WSHs in other species. Future comparative developmental analyses between wings and WSHs may clarify the important steps underlying the evolution of insect wings.     

Multiple dispersals and modern human origins

Despite a massive endeavour, the problem of modern human origins not only remains unresolved, but is usually reduced to “Out of Africa” versus multiregional evolution. Not all would agree, but evidence for a single recent origin is accumulating. Here, we want to go beyond this debate and explore within the “Out of Africa” framework an issue that has not been fully addressed: the mechanism by which modern human diversity has developed. We believe there is no clear rubicon of modern Homo sapiens, and that multiple dispersals occurred from a morphologically variable population in Africa. Pre-existing African diversity is thus crucial to the way human diversity developed outside Africa. The pattern of diversity—behavioural, linguistic, morphological and genetic—can be interpreted as the result of dispersals, colonisation, differentiation and subsequent dispersals overlaid on former population ranges. The first dispersals would have originated in Africa from where two different geographical routes were possible, one through Ethiopia/Arabia towards South Asia, and one through North Africa/Middle East towards Eurasia.     

Fatherhood, pairbonding and testosterone in the Philippines

In species with a high level of paternal care, including humans, testosterone (T) is believed to help mediate the trade-off between parenting and mating effort. This hypothesis is supported by the observation of lower T in pairbonded men or fathers compared to single, non-fathers; however, prior work has highlighted population variation in the association between T and pairbonding or fatherhood status. Here we evaluate this hypothesis in a large (n = 890), representative birth cohort of young men (age range 20.5–22.5 years) living in Cebu City, the Philippines. Bioavailable T was measured in saliva collected prior to bed and immediately upon waking the following morning. Plasma T and luteinizing hormone (LH) were measured in morning plasma samples. In this sample, 20% of men were pairbonded, defined as living with a partner or married, 13% were fathers, and roughly half of fathers reported involvement in childcare. Pairbonded men had significantly lower T at both times of day. Unlike in other populations, this relationship was accounted for entirely by fatherhood status: among the large sub-sample of non-fathers, mean T was nearly identical among pairbonded and single men. There was a strong association between self-reported involvement in childcare and lower evening T, supporting the idea that the evening nadir in T is related to social interactions across the day. Similar relationships were found for total plasma T and LH, suggesting that these relationships are coordinated by centrally-mediated changes in LH secretion. The relatively modest T difference in relation to fatherhood at Cebu, in comparison to other studies, may reflect a lower level of paternal involvement in childcare activities in this population. Our findings using a large, well-characterized birth cohort support the hypothesized role of T as a mediator of mating and parenting effort in humans, while contributing evidence for cultural variation in the relative importance of pairbonding and fathering to these relationships.     

The calcaneus of Australopithecus afarensis and its implications for the evolution of bipedality

Calcanei from African apes, modern humans, and Australopithecus afarensis are compared to investigate the anatomical and mechanical changes that occurred in this bone as a result of the transition to terrestrial bipedality. Features analyzed include the cross-sectional area and volume of the calcaneal tuber, the geometry and orientation of the articular surfaces, and the surface topography of the calcaneal corpus. Calcaneal morphology is unequivocal in its partitioning of quadrupedal pongids and bipedal hominids.     

Hominid taphonomy: Transport of human skeletal parts in an artificial fluviatile environment

Flume experiments demonstrate that human skeletal parts sort into lag and transportable groups in a current flow of 31 cm/sec. Orientations, rates and types of movement, and stable positions are recorded. Density of a skeletal part is correlated with the average rate of movement, whereas wet weight in air, weight in water, and volume are not. Shape is an important but unquantifiable factor. Complete crania are the fastest moving elements; individual cranial fragments are in the lag group. Omo fluviatile deposits show a preponderance of hominid lag elements, whereas Olduvai and East Rudolf perilacustrine deposits present a mixture of transportable and lag elements.     

Hallucal tarsometatarsal joint in Australopithecus afarensis

Hallucal tarsometatarsal joints from African pongids, modern humans, and Australopithecus afarensis are compared to investigate the anatomical and mechanical changes that accompanied the transition to terrestrial bipedality. Features analyzed include the articular orientation of the medial cuneiform, curvature of the distal articular surface of the medial cuneiform, and the articular configuration of the hallucal metatarsal proximal joint surface. Morphological characteristics of the hallucal tarsometatarsal joint unequivocally segregate quadrupedal pongids and bipedal hominids.     

Gene expression profiling of human diseases by serial analysis of gene expression

Until recently, the approach to understanding the molecular basis of complex syndromes such as cancer, coronary artery disease, and diabetes was to study the behavior of individual genes. However, it is generally recognized that expression of a number of genes is coordinated both spatially and temporally and that this coordination changes during the development and progression of diseases. Newly developed functional genomic approaches, such as serial analysis of gene expression (SAGE) and DNA microarrays have enabled researchers to determine the expression pattern of thousands of genes simultaneously. One attractive feature of SAGE compared to microarrays is its ability to quantify gene expression without prior sequence information or information about genes that are thought to be expressed. SAGE has been successfully applied to the gene expression profiling of a number of human diseases. In this review, we will first discuss SAGE technique and contrast it to microarray. We will then highlight new biological insights that have emerged from its application to the study of human diseases.     

Rates of evolution: Is there a conflict between neo-darwinian evolutionary theory and the fossil record?

Neo-darwinian and population genetics theory assumes that the necessary and sufficient set of conditions for all genetic, therefore evolutionary, change has been identified. Punctuationalists have assumed the opposite and cite the fossil record as evidence for change too rapid to be explained in neo-darwinian theory. Data is given here to provide estimates of the rate of evolution in hominid fossils, in living populations, and of that rate which would qualify as punctuational in the hominid fossil record. Evolution in living populations is orders of magnitude greater than that found in the fossil record and far greater than necessary to create apparently instantaneous saltations in the fossil record. It is suggested that such saltations may not represent more rapid rates of evolution but, rather, the persistence of evolutionary change in a given direction for a longer than normal period.     

Gluteus maximus muscle function and the origin of hominid bipedality

Bipedality not only frees the hands for tool use but also enhances tool use by allowing use of the trunk for leverage in applying force and thus imparting greater final velocity to tools. Since the weight and acceleration of the trunk and forelimbs on the hindlimbs must be counteracted by muscles such as m. gluteus maximus that control pelvic and trunk movements, it is suggested that the large size of the cranial portion of the human gluteus maximus muscle and its unique attachment to the dorsal ilium (which is apparent in the Makapan australopithecine ilium) may have contributed to the effectiveness with which trunk movement was exploited in early hominid foraging activities. To test this hypothesis, the cranial portions of both right and left muscles were investigated in six human subjects with electromyography during throwing, clubbing, digging, and lifting. The muscles were found to be significantly recruited when the trunk is used in throwing and clubbing, initiating rotation of the pelvis and braking it as trunk rotation ceases and the forelimb accelerates. They stabilize the pelvis during digging and exhibit marked and prolonged activity when the trunk is maintained in partial flexion during lifting of heavy objects.     

Paternal Care by Genetic Fathers and Stepfathers I: Reports from Albuquerque Men

We present a biosocial model of human male parental care that allows male parental allocations to be influenced not only by changes in the fitness (welfare) of the recipient offspring, but also by their effects on the man's relationship with the child's mother. The model recognizes four classes of relationships between males and the children they parent: genetic offspring of current mates (combined relationship and parental effort), genetic offspring of previous mates (parental effort solely), step offspring of current mates (relationship effort solely), and stepchildren of previous mates (essentially no expected investment). We test the model using data on parental investments collected from adult males living in Albuquerque, New Mexico, U.S.A. Four measures of paternal investment are examined: the probability that a child attends college (2,191 offspring), the probability that a child who attends college receives money for it (N = 1,212), current financial expenditures on children (N = 635), and the amount of time per week that men spend with children ages 5 to 12 years (N = 2,589). The tests are consistent with a role for relationship effort in parental care: men invest more in the children of their current mates, even when coresidence with offspring is not a confounder.     

Primate models for australopithecine sexual dimorphism

Several different models of sexual dimorphism in the South African australopithecines are compared with sexual dimorphism in the living primates. Australopithecine dimorphism is placed in an evolutionary context, and contrasting trends in the hominid and pongid lineages are shown. Evidence suggesting that the australopithecines were an extremely polytypic taxon is presented, and a high level of both inter- and intra-population variation is indicated.     

Stable nitrogen isotope analysis of dentine serial sections elucidate sex differences in weaning patterns of wild chimpanzees (Pan troglodytes)

Offspring provisioning is one of the most energetically demanding aspects of reproduction for female mammals. Variation in lactation length and weaning strategies between chimpanzees (Pan troglodytes), our closest living relative, and modern human societies have been reported. When and why these changes occurred is frequently debated. Our study used stable nitrogen isotope data of tooth root dentine from wild Western chimpanzees (Pan troglodytes verus) in Taï National Park, Côte d'Ivoire, to quantify weaning in these chimpanzees and explore if infant sex plays a role in maternal investment. We analyzed serial sections of deciduous lateral incisor root dentine from four Taï chimpanzees to establish the δ¹⁵N signal of nursing infants; we then analyzed serial sections of first permanent mandibular molar root dentine from 12 Taï chimpanzees to provide quantitative δ¹⁵N data on weaning in this population. Up to 2 years of age both sexes exhibited dentine δ¹⁵N values ≈2–3‰ higher than adult female Taï chimpanzees, consistent with a nursing signal. Thereafter a steady decrease in δ¹⁵N values consistent with the onset, and progression, of weaning, was visible. Sex differences were also evident, where male δ¹⁵N values decreased at a significantly slower rate compared to females. Confirmation of sex differences in maternal investment among Taï chimpanzees, demonstrates the viability of using isotope analysis to investigate weaning in non‐human primates. Additionally, assuming that behaviors observed in the Taï chimpanzees are illustrative of the ancestral pattern, our results provide a platform to enable the trajectory of weaning in human evolution to be further explored. Am J Phys Anthropol 153:635–642, 2014. © 2013 Wiley Periodicals, Inc.     

Cranial capacity evolution in Homo erectus and early Homo sapiens.

This paper investigates patterns of cranial capacity evolution in Homo erectus, early Homo sapiens, and in regional subsamples of H. erectus. Specifically, models explaining evolution of cranial capacity in these taxa are evaluated with statistical techniques developed for the analysis of time series data. Regression estimates of rates of evolution in cranial capacity are also obtained. A non-parametric test for trend suggests that cranial capacity in both H. erectus and early H. sapiens may increase significantly through time. Cranial capacity in an Asian subsample of H. erectus (comprised of Chinese and Indonesian specimens) increases significantly through time. Other subsamples of H. erectus (African, Chinese, and Indonesian) do not appear to increase significantly through time. Regression results generally corroborate results of the test for trend. Spatial and temporal variation may characterize evolution of cranial capacity in H. erectus. Different patterns of cranial capacity evolution may distinguish H. erectus from early H. sapiens.     

Perceived mate fidelity and paternal resemblance predict men's investment in children

Here, we investigate whether variation in male parental investment can be explained in terms of (1) men's perception of the degree of resemblance between themselves and their offspring and (2) men's perception of their mates' fidelity. In a sample of men from London's Heathrow airport, both variables were found to predict reported investment. We also examined whether the predictors of investment varied when men were no longer in a relationship with the mother of their children and are therefore no longer investing in mating effort with them. Among men no longer in a relationship with the mother of their children, resemblance became a stronger predictor of investment, while fidelity was no longer a significant predictor. Overall, men provided less investment to their children if they were no longer in a relationship with the mother of their children.     

Hominid Brain Evolution

Hypotheses regarding the selective pressures driving the threefold increase in the size of the hominid brain since Homo habilis include climatic conditions, ecological demands, and social competition. We provide a multivariate analysis that enables the simultaneous assessment of variables representing each of these potential selective forces. Data were collated for latitude, prevalence of harmful parasites, mean annual temperature, and variation in annual temperature for the location of 175 hominid crania dating from 1.9 million to 10 thousand years ago. We also included a proxy for population density and two indexes of paleoclimatic variability for the time at which each cranium was discovered. Results revealed independent contributions of population density, variation in paleoclimate, and temperature variation to the prediction of change in hominid cranial capacity (CC). Although the effects of paleoclimatic variability and temperature variation provide support for climatic hypotheses, the proxy for population density predicted more unique variance in CC than all other variables. The pattern suggests multiple pressures drove hominid brain evolution and that the core selective force was social competition. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Anterior dental cutting in the Laetolil hominids and the evolution of the bicuspid P3

The younger Laetolil hominids provide evidence of a unique anterior cutting complex with a chisel-like action occurring between the lingual-distal C face and a transverse ridge on the P₃ perpendicular to it, extending between the subequal cusps. An earlier adaptation to more efficient grinding may have resulted in reduced canine projection and the development of the lingual P₃ cusp, raising the ridge between it and the buccal cusp. This development acted to retain the anterior cutting function by shifting it to the top of the premolar.     

Paternal Care by Genetic Fathers and Stepfathers II: Reports by Xhosa High School Students

In this article we present a biosocial model of human male parental care that allows relationship (mating) effort to influence male parental allocations. The model recognizes four classes of relationships between men and the children they parent: genetic offspring of current mates (combined relationship and parental effort), genetic offspring of previous mates (parental effort solely), step offspring of current mates (relationship effort solely), and stepchildren of previous mates (essentially no expected investment). We test the model using data on parental investment collected from 340 Xhosa high school students in Cape Town, South Africa. Six measures of paternal investment are examined: the amount of money men spent on students for school, clothing, and miscellaneous expenditures, respectively, and how often men spent time with children, helped them with their homework, or spoke English with them. The tests provide support for the roles of both parental and relationship effort in influencing parental care: men invest significantly more in their genetic offspring and in the children of their current mates. We also examine several proximate influences on parental care, specifically the age and sex of the child, and the percentage of the child's life the father figure coresided with him or her.