High rate of extrapair paternity in a human population demonstrates diversity in human reproductive strategies.

Among nonhuman species, social monogamy is rarely accompanied by complete fidelity. Evolutionary theory predicts that the rate of extrapair paternity (EPP) should vary according to socioecological conditions. In humans, however, geneticists contend that EPP is negligible and relatively invariable. This conclusion is based on a limited set of studies, almost all of which describe European-descent groups. Using a novel, double-blind method designed in collaboration with a community of Himba pastoralists, we find that the rate of EPP in this population is 48%, with 70% of couples having at least one EPP child. Both men and women were very accurate at detecting cases of EPP. These data suggest that the range of variation in EPP across human populations is substantially greater than previously thought. We further show that a high rate of EPP can be accompanied by high paternity confidence, which highlights the importance of disaggregating EPP from the notion of "cuckoldry.

Short-term resource allocation during extensive athletic competition

Abstract Objectives: Following predictions from life history theory, we sought to identify acute trade-offs between reproductive effort (as measured by psychological arousal) and somatic maintenance (via functional measures of innate immunity) during conditions of severe energetic imbalance. Methods: Sixty-six male ultramarathon runners (ages 20 to 37 years) were sampled before and after a lengthy race. Saliva and sera were collected for testosterone and immunological analyses (hemolytic complement activity and bacterial killing ability). Lean body mass was assessed by bioelectrical impedance, and libido was measured using a slideshow of arousing and neutral images. Results: Following predictions, there was a significant decrease in salivary testosterone levels (109.59 pg/mL versus 97.61 pg/mL, P<.001) and arousal scores in response to provocative images (5.40 versus 4.89, P5.001) between prerace and postrace time points. Additionally, participant bacterial killing ability (P5.035) and hemolytic complement activity (P5.021) increased between prerace and postrace. Conclusions: Decreased libido and testosterone with concomitant heightened innate immune responses suggest a shift in energetic priorities away from reproduction and toward maintenance/defense during a period of energetic stress

Inhibition of E2-induced expression of BRCA1 by persistent organochlorines

BACKGROUND: Environmental persistent organochlorines (POCs) biomagnify in the food chain, and the chemicals are suspected of being involved in a broad range of human malignancies. It is speculated that some POCs that can interfere with estrogen receptor-mediated responses are involved in the initiation and progression of human breast cancer. The tumor suppressor gene BRCA1 plays a role in cell-cycle control, in DNA repair, and in genomic stability, and it is often downregulated in sporadic mammary cancers. The aim of the present study was to elucidate whether POCs have the potential to alter the expression of BRCA1. METHODS: Using human breast cancer cell lines MCF-7 and MDA-MB-231, the effect on BRCA1 expression of chemicals belonging to different classes of organochlorine chemicals (the pesticide toxaphene, 2,3,7,8-tetrachlorodibenzo-p-dioxin, and three polychlorinated biphenyls [PCB#138, PCB#153 and PCB#180]) was measured by a reporter gene construct carrying 267 bp of the BRCA1 promoter. A twofold concentration range was analyzed in MCF-7, and the results were supported by northern blot analysis of BRCA1 mRNA using the highest concentrations of the chemicals. RESULTS: All three polychlorinated biphenyls and 2,3,7,8-tetrachlorodibenzo-p-dioxin reduced 17β-estradiol (E2)-induced expression as well as basal reporter gene expression in both cell lines, whereas northern blot analysis only revealed a downregulation of E2-induced BRCA1 mRNA expression in MCF-7 cells. Toxaphene, like E2, induced BRCA1 expression in MCF-7. CONCLUSION: The present study shows that some POCs have the capability to alter the expression of the tumor suppressor gene BRCA1 without affecting the cell-cycle control protein p21(Waf/Cip1). Some POCs therefore have the potential to affect breast cancer risk

Increased homozygosity due to endogamy results in fitness consequences in a human population

Recessive alleles have been shown to directly affect both human Mendelian disease phenotypes and complex traits. Pedigree studies also suggest that consanguinity results in increased childhood mortality and adverse health phenotypes, presumably through penetrance of recessive mutations. Here, we test whether the accumulation of homozygous, recessive alleles decreases reproductive success in a human population. We address this question among the Namibian Himba, an endogamous agro-pastoralist population, who until very recently practiced natural fertility. Using a sample of 681 individuals, we show that Himba exhibit elevated levels of "inbreeding," calculated as the fraction of the genome in runs of homozygosity (FROH). Many individuals contain multiple long segments of ROH in their genomes, indicating that their parents had high kinship coefficients. However, we do not find evidence that this is explained by first-cousin consanguinity, despite a reported social preference for cross-cousin marriages. Rather, we show that elevated haplotype sharing in the Himba is due to a bottleneck, likely in the past 60 generations. We test whether increased recessive mutation load results in observed fitness consequences by assessing the effect of FROH on completed fertility in a cohort of postreproductive women (n = 69). We find that higher FROH is significantly associated with lower fertility. Our data suggest a multilocus genetic effect on fitness driven by the expression of deleterious recessive alleles, especially those in long ROH. However, these effects are not the result of consanguinity but rather elevated background identity by descent