The transition from quantity to quality: a neglected causal mechanism in accounting for social evolution.
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Students of social evolution are concerned not only with the general course it has followed, but also with the mechanisms that have brought it about. One such mechanism comes into play when the quantitative increase in some entity, usually population, reaching a certain threshold, gives rise to a qualitative change in the structure of a society. This mechanism, first recognized by Hegel, was seized on by Marx and Engels. However, neither they nor their current followers among anthropologists have made much use of it in attempting to explain social evolution. But as this paper attempts to show, in those few instances when the mechanism has been invoked, it has heightened our understanding of the process of social evolution. And, it is argued, if the mechanism were more widely applied, further understanding of the course of evolution could be expected to result. (+info)
Haplotypes at ATM identify coding-sequence variation and indicate a region of extensive linkage disequilibrium.
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Genetic variation in the human population may lead to functional variants of genes that contribute to risk for common chronic diseases such as cancer. In an effort to detect such possible predisposing variants, we constructed haplotypes for a candidate gene and tested their efficacy in association studies. We developed haplotypes consisting of 14 biallelic neutral-sequence variants that span 142 kb of the ATM locus. ATM is the gene responsible for the autosomal recessive disease ataxia-telangiectasia (AT). These ATM noncoding single-nucleotide polymorphisms (SNPs) were genotyped in nine CEPH families (89 individuals) and in 260 DNA samples from four different ethnic origins. Analysis of these data with an expectation-maximization algorithm revealed 22 haplotypes at this locus, with three major haplotypes having frequencies > or = .10. Tests for recombination and linkage disequilibrium (LD) show reduced recombination and extensive LD at the ATM locus, in all four ethnic groups studied. The most striking example was found in the study population of European ancestry, in which no evidence for recombination could be discerned. The potential of ATM haplotypes for detection of genetic variants through association studies was tested by analysis of 84 individuals carrying one of three ATM coding SNPs. Each coding SNP was detected by association with an ATM haplotype. We demonstrate that association studies with haplotypes for candidate genes have significant potential for the detection of genetic backgrounds that contribute to disease. (+info)
Endogenous biosynthesis of thromboxane and prostacyclin in 2 distinct murine models of atherosclerosis.
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Thromboxane A(2) is a potent vasoconstrictor and platelet agonist; prostacyclin is a potent platelet inhibitor and vasodilator. Altered biosynthesis of these eicosanoids is a feature of human hypercholesterolemia and atherosclerosis. This study examined whether in 2 murine models of atherosclerosis their levels are increased and correlated with the evolution of the disease. Urinary 2,3-dinor thromboxane B(2) and 2,3-dinor-6-keto prostaglandin F(1 alpha), metabolites of thromboxane and prostacyclin, respectively, were assayed in apoliprotein E (apoE)-deficient mice on chow and low-density lipoprotein receptor (LDLR)-deficient mice on chow and a Western-type diet. Atherosclerosis lesion area was measured by en face method. Both eicosanoids increased in apoE-deficient mice on chow and in LDLR-deficient mice on a high-fat diet, but not in LDLR-deficient mice on chow by the end of the study. Aspirin suppressed ex vivo platelet aggregation, serum thromboxane B(2), and 2,3-dinor thromboxane B(2), and significantly reduced the excretion of 2,3-dinor-6-keto prostaglandin F(1 alpha) in these animals. This study demonstrates that thromboxane as well as prostacyclin biosynthesis is increased in 2 murine models of atherogenesis and is secondary to increased in vivo platelet activation. Assessment of their generation in these models may afford the basis for future studies on the functional role of these eicosanoids in the evolution and progression of atherosclerosis. (Blood. 2000;96:3823-3826) (+info)
Diet and the evolution of the earliest human ancestors.
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Over the past decade, discussions of the evolution of the earliest human ancestors have focused on the locomotion of the australopithecines. Recent discoveries in a broad range of disciplines have raised important questions about the influence of ecological factors in early human evolution. Here we trace the cranial and dental traits of the early australopithecines through time, to show that between 4.4 million and 2.3 million years ago, the dietary capabilities of the earliest hominids changed dramatically, leaving them well suited for life in a variety of habitats and able to cope with significant changes in resource availability associated with long-term and short-term climatic fluctuations. (+info)
Evolution of the X-linked zinc finger gene and the Y-linked zinc finger gene in primates.
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We have sequenced the partial exon of the zinc finger genes (ZFX and ZFY) in 5 hominoids, 2 Old World monkeys, 1 New World monkey, and 1 prosimian. Among these primate species, the percentage similarities of the nucleotide sequence of the ZFX gene were 96-100% and 91.2-99.7% for the ZFY gene. Of 397 sites in the ZFX and ZFY gene sequences, 20 for ZFX gene and 42 for ZFY gene were found to be variable. Substitution causes 1 amino acid change in ZFX, and 5 in ZFY, among 132 amino acids. The numbers of synonymous substitutions per site (Ks) between human and the chimpanzee, gorilla and orangutan for ZFY gene were 0.026, 0.033, and 0.085, respectively. In contrast, the Ks value between human and hominoid primates for the ZFX gene was 0.008 for each comparison. Comparison of the ZFX and ZFY genes revealed that the synonymous substitution levels were higher in hominoids than in other primates. The rates of synonymous substitution per site per year were higher in the ZFY exon than in the SRY exon, and higher in the ZFY exon than in the ZFY intron, in hominoid primates. (+info)
Phylogenetic analysis of a retroposon family as represented on the human X chromosome.
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SINE-R elements constitute a class of retroposons derived from the long terminal repeat (LTR) of the human endogenous retrovirus HERV-K family that are present in hominoid primates and active in the human genome. In an investigation of the X chromosome, we identified twenty-five SINE-R elements with between 89.6 and 97.7% homology with the SINE-R.C2 element that is human specific, originally identified in the gene for the C2 component of complement. SINE-R.C2 and a sequence HS307 that we previously identified in a region of Xq21.3 that has a recently created homology with a 4 Mb block in Yp11.2 are amongst the group of elements that have diverged furthest from the parent HERV-K10 sequence. The sequence on the X chromosome resemble those that we previously described on chromosomes 7 and 17 and the Y chromosome, with a similar range of variation. Phylogenetic analysis from the retroposon family including those of African great apes using the neighbor-joining method suggests that the SINE-R retroposon family have evolved independently during primate evolution. Further investigation of SINE-R elements on the sex chromosomes, particularly in recently created regions of X-Y homology, may cast light on the timing of the retroposition process and its possible relevance to recent evolutionary change. (+info)
The primate appendix: a reassessment.
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The presence of a vermiform appendix is often cited as a shared, derived character uniting the Hominoidea (apes and humans). However, appendix-like structures have been reported for many other primate taxa. A review of the literature reveals that the confusion arises because several different, and sometimes contradictory, criteria are enlisted to distinguish an appendix. The measures most frequently used to define this structure are gross shape and certain aspects of histology (e.g., lymphoid concentration). Unfortunately, descriptions of shape lack quantification, and histological thin-sections have not been studied for many primate taxa. In addition, although lymphoid concentration in the human appendix is known to vary considerably with age, this information is rarely reported in the primate literature. Given these complications, additional studies on the morphology and ontogeny of this region are warranted. This research will lead to a more accurate definition of the vermiform appendix. Most authors currently describe this feature as a narrow diverticulum of the cecum with thick walls and concentrated lymphoid tissue. However, the presence of thick mucosal layers and appreciable lymphoid tissue in taxa lacking appendices (e. g., Saguinus, Cercocebus) suggests that these features may be primitive primate traits. If so, wall thickness and lymphoid concentration cannot be used to define the vermiform appendix. These results suggest that a more rigorous definition of the appendix is requisite for this feature to be used in primate systematics. (+info)
Digital imaging of bone and tooth modification.
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Digital cameras are capable of producing images of cut marks and other three dimensional subjects comparable to those obtained from the scanning electron microscope (SEM). Until now, the SEM has offered unparalleled depth of field and surface rendition. SEM units are, however, expensive to acquire and maintain, and SEM image production is time-intensive. Furthermore, SEM images lack color and are often incapable of imaging bone modifications because of magnification and chamber size limitations. A digital imaging method for producing extremely high depth of field enlargements of three dimensional, sub-millimeter scale objects circumvents these problems. In our presentation we employ four case studies of hard tissue modification related to: (1) the origins of meat-eating in the human lineage; (2) evidence for cannibalistic behavior among Neanderthals; (3) pre-Columbian evidence of North American dentistry; and (4) the earliest evidence of cranial surgery in North America. Procedures for replica production, image-capture, and image enhancement are provided. The digital images produced are compared to those obtained with the SEM. Image processing software, a crucial component of this method, allows complete control of graphic data, making graphic fraud a larger threat than ever before. Issues in ethics stemming from the application of this technology to scientific analysis are considered. (+info)