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Impairment in reciprocal social behavior (RSB), an essential component of early social competence, clinically defines autism spectrum disorder (ASD). However, the behavioral and genetic architecture of RSB in toddlerhood, when ASD first emerges, has not been fully characterized. We analyzed data from a quantitative video-referenced rating of RSB (vrRSB) in two toddler samples: a community-based volunteer research registry (n = 1,563) and an ethnically diverse, longitudinal twin sample ascertained from two state birth registries (n = 714). Variation in RSB was continuously distributed, temporally stable, significantly associated with ASD risk at age 18 months, and only modestly explained by sociodemographic and medical factors (r2 = 9.4%). Five latent RSB factors were identified and corresponded to aspects of social communication or restricted repetitive behaviors, the two core ASD symptom domains. Quantitative genetic analyses indicated substantial heritability for all factors at age 24 months (h2 ≥ .61). Genetic influences strongly overlapped across all factors, with a social motivation factor showing evidence of newly-emerging genetic influences between the ages of 18 and 24 months. RSB constitutes a heritable, trait-like competency whose factorial and genetic structure is generalized across diverse populations, demonstrating its role as an early, enduring dimension of inherited variation in human social behavior. Substantially overlapping RSB domains, measurable when core ASD features arise and consolidate, may serve as markers of specific pathways to autism and anchors to inform determinants of autism's heterogeneity.
Diet modifies the risk of colorectal cancer (CRC), and inconclusive evidence suggests that yogurt may protect against CRC. We analysed the data collected from two separate colonoscopy-based case–control studies. The Tennessee Colorectal Polyp Study (TCPS) and Johns Hopkins Biofilm Study included 5446 and 1061 participants, respectively, diagnosed with hyperplastic polyp (HP), sessile serrated polyp, adenomatous polyp (AP) or without any polyps. Multinomial logistic regression models were used to derive OR and 95 % CI to evaluate comparisons between cases and polyp-free controls and case–case comparisons between different polyp types. We evaluated the association between frequency of yogurt intake and probiotic use with the diagnosis of colorectal polyps. In the TCPS, daily yogurt intake v. no/rare intake was associated with decreased odds of HP (OR 0·54; 95 % CI 0·31, 0·95) and weekly yogurt intake was associated with decreased odds of AP among women (OR 0·73; 95 % CI 0·55, 0·98). In the Biofilm Study, both weekly yogurt intake and probiotic use were associated with a non-significant reduction in odds of overall AP (OR 0·75; 95 % CI 0·54, 1·04) and (OR 0·72; 95 % CI 0·49, 1·06) in comparison with no use, respectively. In summary, yogurt intake may be associated with decreased odds of HP and AP and probiotic use may be associated with decreased odds of AP. Further prospective studies are needed to verify these associations.
Sexually selected infanticide is relatively widespread among primates, but has been documented primarily in one-male–multifemale reproductive units, e.g., in guenons (Cercopithecus spp.) (Butynski 1982; Fairgrieve 1995), langurs (Presbytis spp.) (Hrdy 1974; Newton 1988; Sommer 1994), howler monkeys (Alouatta spp.) (Crockett & Sekulic 1984), and mountain gorillas (Gorilla gorilla berengei) (Fossey 1984; Watts 1989). Although male infanticide has been invoked as a selective force in multimale–multifemale groups, such as in macaques (Macaca fascicularis) (van Noordwijk 1985), capuchin monkeys (Cebus olivaceus) (O'Brien 1991), and chimpanzees (Pan troglodytes) (Smuts & Smuts 1993), it has rarely been observed in these species (e.g., Valderrama et al. 1990; Camperio Ciani 1984) or follows patterns partly inconsistent with Hrdy's (1974) sexual selection hypothesis (Hiraiwa-Hasegawa & Hasegawa 1994). Thus current data suggest that the presence of multiple males in a primate group discourages infant-killing by other males.
Relative to one-male groups, the presence of additional, reproductively active males may both dilute the benefits of infanticide and increase its costs. Exploitation of the reproductive opportunity created by infanticide depends upon the perpetrator's ability to monopolize subsequent fertilizations, which is a function of social variables such as the number of males in a group, the intensity of male–male mating competition, and the potential for effective mate guarding.
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