Microscopic investigation in fossil hominoidea: a clue to taxonomy, functional anatomy, and the history of diseases.
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Ten selected samples of fossilized bones (including Australopithecus, Homo erectus, Homo neandertalensis, and Homo sapiens sapiens) were examined by light microscopy using plane and polarized light. The histomorphological findings show that microscopic research adds much to what can be ascertained by marcoscopic examination or by X-ray techniques. In particular, emphasis was placed on taxonomy, functional anatomy of bones, and causes of some of the diseases of early hominids. Anat Rec (New Anat): 257:225-232, 1999. (+info)
Morphological variation in great ape and modern human mandibles.
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Adult mandibles of 317 modern humans and 91 great apes were selected that showed no pathology. Adult mandibles of Pan troglodytes troglodytes, Pongo pygmaeus pygmaeus and Gorilla gorilla gorilla and from 2 modern human populations (Zulu and Europeans from Spitalfields) were reliably sexed. Thirteen measurements were defined and included mandibular height, length and breadth in representative positions. Univariate statistical techniques and multivariate (principal component analysis and discriminant analysis) statistical techniques were used to investigate interspecific variability and sexual dimorphism in human and great ape mandibles, and intraspecific variability among the modern human mandibles. Analysis of interspecific differences revealed some pairs of variables with a tight linear relationship and others where Homo and the great apes pulled apart from one another due to shape differences. Homo and Pan are least sexually dimorphic in the mandible, Pan less so than Homo sapiens, but both the magnitude of sexual dimorphism and the distribution of sexually dimorphic measurements varied both among and between modern humans and great apes. Intraspecific variation among the 10 populations of modern humans was less than that generally reported in studies of crania (74.3% of mandibles were correctly classified into 1 of 10 populations using discriminant functions based on 13 variables as compared with 93% of crania from 17 populations based on 70 variables in one extensive study of crania). A subrecent European population (Poundbury) emerged as more different from a recent European population (Spitalfields) than other more diverse modern populations were from each other, suggesting considerable morphological plasticity in the mandible through time. This study forms a sound basis on which to explore mandibular variation in Neanderthals, early Homo sapiens and other more ancient fossil hominids. (+info)
Population bottlenecks and Pleistocene human evolution.
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We review the anatomical and archaeological evidence for an early population bottleneck in humans and bracket the time when it could have occurred. We outline the subsequent demographic changes that the archaeological evidence of range expansions and contractions address, and we examine how inbreeding effective population size provides an alternative view of past population size change. This addresses the question of other, more recent, population size bottlenecks, and we review nonrecombining and recombining genetic systems that may reflect them. We examine how these genetic data constrain the possibility of significant population size bottlenecks (i.e., of sufficiently small size and/or long duration to minimize genetic variation in autosomal and haploid systems) at several different critical times in human history. Different constraints appear in nonrecombining and recombining systems, and among the autosomal loci most are incompatible with any Pleistocene population size expansions. Microsatellite data seem to show Pleistocene population size expansions, but in aggregate they are difficult to interpret because different microsatellite studies do not show the same expansion. The archaeological data are only compatible with a few of these analyses, most prominently with data from Alu elements, and we use these facts to question whether the view of the past from analysis of inbreeding effective population size is valid. Finally, we examine the issue of whether inbreeding effective population size provides any reasonable measure of the actual past size of the human species. We contend that if the evidence of a population size bottleneck early in the evolution of our lineage is accepted, most genetic data either lack the resolution to address subsequent changes in the human population or do not meet the assumptions required to do so validly. It is our conclusion that, at the moment, genetic data cannot disprove a simple model of exponential population growth following a bottleneck 2 MYA at the origin of our lineage and extending through the Pleistocene. Archaeological and paleontological data indicate that this model is too oversimplified to be an accurate reflection of detailed population history, and therefore we find that genetic data lack the resolution to validly reflect many details of Pleistocene human population change. However, there is one detail that these data are sufficient to address. Both genetic and anthropological data are incompatible with the hypothesis of a recent population size bottleneck. Such an event would be expected to leave a significant mark across numerous genetic loci and observable anatomical traits, but while some subsets of data are compatible with a recent population size bottleneck, there is no consistently expressed effect that can be found across the range where it should appear, and this absence disproves the hypothesis. (+info)
Mid-Pleistocene Acheulean-like stone technology of the Bose basin, South China.
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Stone artifacts from the Bose basin, South China, are associated with tektites dated to 803,000 +/- 3000 years ago and represent the oldest known large cutting tools (LCTs) in East Asia. Bose toolmaking is compatible with Mode 2 (Acheulean) technologies in Africa in its targeted manufacture and biased spatial distribution of LCTs, large-scale flaking, and high flake scar counts. Acheulean-like tools in the mid-Pleistocene of South China imply that Mode 2 technical advances were manifested in East Asia contemporaneously with handaxe technology in Africa and western Eurasia. Bose lithic technology is associated with a tektite airfall and forest burning. (+info)
Loss of N-glycolylneuraminic acid in human evolution. Implications for sialic acid recognition by siglecs.
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The common sialic acids of mammalian cells are N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc). Humans are an exception, because of a mutation in CMP-sialic acid hydroxylase, which occurred after our common ancestor with great apes. We asked if the resulting loss of Neu5Gc and increase in Neu5Ac in humans alters the biology of the siglecs, which are Ig superfamily members that recognize sialic acids. Human siglec-1 (sialoadhesin) strongly prefers Neu5Ac over Neu5Gc. Thus, humans have a higher density of siglec-1 ligands than great apes. Siglec-1-positive macrophages in humans are found primarily in the perifollicular zone, whereas in chimpanzees they also occur in the marginal zone and surrounding the periarteriolar lymphocyte sheaths. Although only a subset of chimpanzee macrophages express siglec-1, most human macrophages are positive. A known evolutionary difference is the strong preference of mouse siglec-2 (CD22) for Neu5Gc, contrasting with human siglec-2, which binds Neu5Ac equally well. To ask when the preference for Neu5Gc was adjusted in the human lineage, we cloned the first three extracellular domains of siglec-2 from all of the great apes and examined their preference. In fact, siglec-2 had evolved a higher degree of recognition flexibility before Neu5Gc was lost in humans. Human siglec-3 (CD33) and siglec-6 (obesity-binding protein 1) also recognize both Neu5Ac and Neu5Gc, and siglec-5 may have some preference for Neu5Gc. Others showed that siglec-4a (myelin-associated glycoprotein) prefers Neu5Ac over Neu5Gc. Thus, the human loss of Neu5Gc may alter biological processes involving siglec-1, and possibly, siglec-4a or -5. (+info)
Endocranial capacity in Sts 71 (Australopithecus africanus) by three-dimensional computed tomography.
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In a recent report on early hominid endocranial capacity, it was predicted that future studies would show that: (1) "several key early hominid endocranial estimates may be inflated"; (2) "current views on the tempo and mode of early hominid brain evolution may need reevaluation"; and (3) endocranial capacity in one of these, Sts 71, was "probably closer to 370 cm(3), very near the mean value for female chimpanzees, and not the currently accepted 428 cm(3)" (Conroy et al., Science, 1998; 280: 1730-1731; Falk, Science 1998; 20:1714). Subsequent studies tend to support the first two predictions, but not the third (Culotta, Science, 1999; 284: 1109; Falk, Am. J. Phys. Anthropol. Suppl., 1999; 28: 126; Falk et al., J. Hum. Evol. [in press]). Here we detail the reasons for thinking the currently accepted endocranial value for Sts 71 is probably correct by providing the first quantitative details of endocranial reconstruction in Sts 71 using three-dimensional computed tomography. Relative brain expansion in the hominid lineage started some half-million years before the earliest appearance of the genus Homo, possibly coincident with enhanced tool-making skills and carnivory. (+info)
Human population expansion and microsatellite variation.
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Polymorphisms at di-, tri-, and tetranucleotide microsatellite loci have been analyzed in 14 worldwide populations. A statistical index of population expansion, denoted S(k), is introduced to detect historical changes in population size using the variation at the microsatellites. The index takes the value 0 at equilibrium with constant population size and is positive or negative according to whether the population is expanding or contracting, respectively. The use of S(k) requires estimation of properties of the mutation distribution for which we use both family data of Dib et al. for dinucleotide loci and our population data on tri- and tetranucleotide loci. Statistical estimates of the expansion index, as well as their confidence intervals from bootstrap resampling, are provided. In addition, a dynamical analysis of S(k) is presented under various assumptions on population growth or decline. The studied populations are classified as having high, intermediate, or low values of S(k) and genetic variation, and we use these to interpret the data in terms of possible population dynamics. Observed values of S(k) for samples of di-, tri-, and tetranucleotide data are compatible with population expansion earlier than 60,000 years ago in Africa, Asia, and Europe if the initial population size before the expansion was on the order of 500. Larger initial population sizes force the lower bound for the time since expansion to be much earlier. We find it unlikely that bottlenecks occurred in Central African, East Asian, or European populations, and the estimated expansion times are rather similar for all of these populations. This analysis presented here suggests that modern human populations departed from Africa long before they began to expand in size. Subsequently, the major groups (the African, East Asian, and European groups) started to grow at approximately same time. Populations of South America and Oceania show almost no growth. The Mbuti population from Zaire appears to have experienced a bottleneck during its expansion. (+info)
Sex chromosomal transposable element accumulation and male-driven substitutional evolution in humans.
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We sequenced the genomic region containing the human Y-linked zinc finger gene (ZFY). Comparison of ZFY to the related region on the X chromosome (ZFX) and to autosomal sequences reveals a significant accumulation of transposable elements on the sex chromosomes. In addition, five times as many retroviruslike elements (RLEs) are present in the ZFY region as in the ZFX region. Thus, transposable elements accumulate more rapidly on the sex chromosomes, and the insertion of RLEs may occur more frequently in the male than in the female germ line. When the accumulation of substitutions in Alu elements was analyzed, it was found that the Alu elements at the Y-chromosomal locus diverged significantly faster than those at the X-chromosomal locus, whereas the divergence of autosomal Alu elements was intermediate. The male-to-female mutation rate ratio was estimated to be 2.5. (+info)