After short interbirth intervals, captive callitrichine monkeys have higher infant mortality.

Life history theory predicts a trade-off between the quantity and quality of offspring. Short interbirth intervals-the time between successive births-may increase the quantity of offspring but harm offspring quality. In contrast, long interbirth intervals may bolster offspring quality while reducing overall reproductive output. Further research is needed to determine whether this relationship holds among primates, which have intensive parental investment. Using Cox proportional hazards models, we examined the effects of interbirth intervals (short, normal, or long) on infant survivorship using a large demographic dataset (n = 15,852) of captive callitrichine monkeys (marmosets, tamarins, and lion tamarins). In seven of the nine species studied, infants born after short interbirth intervals had significantly higher risks of mortality than infants born after longer interbirth intervals. These results suggest that reproduction in callitrichine primates may be limited by physiologic constraints, such that short birth spacing drives higher infant mortality.

Postpartum depression and mother-offspring conflict over maternal investment.

BACKGROUND AND OBJECTIVES: As the mother-offspring relationship is central to human reproduction, postpartum depression symptoms are difficult to explain in evolutionary terms. We proposed that postpartum depression might arise as a result of evolutionary mother-offspring conflict over maternal investment, and investigated the association between postpartum depression symptoms, infant night waking, maternal sleep disturbance and breastfeeding frequency. METHODOLOGY: We conducted a cross-sectional analysis using survey responses at 6 months postpartum from 1598 Finnish mothers. We hypothesized that infant night waking at 6 months postpartum would be associated with postpartum depression symptoms, and that this association would be mediated by maternal sleep disturbance and a higher breastfeeding frequency. RESULTS: Infant night waking was moderately associated with postpartum depression symptoms, and this association was mediated by maternal sleep disturbance (R 2=0.09). Contrary to our prediction, we found that increased breastfeeding was associated with less postpartum depression symptoms. CONCLUSIONS AND IMPLICATIONS: We conclude that postpartum depression symptoms might partly be the result of increased maternal fatigue stemming from high offspring demands on maternal investment, but that this is not due to the metabolic strain from increased breastfeeding. Studying postpartum depression from the mother-offspring conflict perspective can potentially improve our understanding of the involved behavioral processes of both mother and offspring, and allow interventions designed to benefit the well-being of both parties. Lay Summary: We proposed that postpartum depression is due to an evolutionary conflict between mother and infant, where the infant tires the mother to delay the arrival of a sibling. We found a link between infant night waking and postpartum depression, mediated by the mother's sleep, but not by breastfeeding frequency.

A comparative study of litter size and sex composition in a large dataset of callitrichine monkeys.

In many birds and mammals, the size and sex composition of litters can have important downstream effects for individual offspring. Primates are model organisms for questions of cooperation and conflict, but the factors shaping interactions among same-age siblings have been less-studied in primates because most species bear single young. However, callitrichines (marmosets, tamarins, and lion tamarins) frequently bear litters of two or more, thereby providing the opportunity to ask whether variation in the size and sex composition of litters affects development, survival, and reproduction. To investigate these questions, we compiled a large dataset of nine species of callitrichines (n = 27,080 individuals; Callithrix geoffroyi, Callithrix jacchus, Cebuella pygmaea, Saguinus imperator, Saguinus oedipus, Leontopithecus chrysomelas, Leontopithecus chrysopygus, Leontopithecus rosalia, and Callimico goeldii) from zoo and laboratory populations spanning 80 years (1938-2018). Through this comparative approach, we found several lines of evidence that litter size and sex composition may impact fitness. Singletons have higher survivorship than litter-born peers and they significantly outperform litter-born individuals on two measures of reproductive performance. Further, for some species, individuals born in a mixed-sex litter outperform isosexually-born individuals (i.e., those born in all-male or all-female litters), suggesting that same-sex competition may limit reproductive performance. We also document several interesting demographic trends. All but one species (C. pygmaea) has a male-biased birth sex ratio with higher survivorship from birth to sexual maturity among females (although this was significant in only two species). Isosexual litters occurred at the expected frequency (with one exception: C. pygmaea), unlike other animals, where isosexual litters are typically overrepresented. Taken together, our results indicate a modest negative effect of same-age sibling competition on reproductive output in captive callitrichines. This study also serves to illustrate the value of zoo and laboratory records for biological inquiry.

Response to vocal music in Angelman syndrome contrasts with Prader-Willi syndrome.

Parent-offspring conflict-conflict over resource distribution within families due to differences in genetic relatedness-is the biological foundation for many psychological phenomena. In genomic imprinting disorders, parent-specific genetic expression is altered causing imbalances in behaviors influenced by parental investment. We use this natural experiment to test the theory that parent-offspring conflict contributed to the evolution of vocal music by moderating infant demands for parental attention. Individuals with Prader-Willi syndrome, a genomic imprinting disorder resulting from increased relative maternal genetic contribution, show enhanced relaxation responses to song, consistent with reduced demand for parental investment (Mehr et al., 2017, Psychological Science). We report the necessary complementary pattern here: individuals with Angelman syndrome, a genomic imprinting disorder resulting from increased relative paternal genetic contribution, demonstrate a relatively reduced relaxation response to song, suggesting increased demand for parental attention. These results support the extension of genetic conflict theories to psychological resources like parental attention.

The tempo of human childhood: a maternal foot on the accelerator, a paternal foot on the brake.

Relative to the life history of other great apes, that of humans is characterized by early weaning and short interbirth intervals (IBIs). We propose that in modern humans, birth until adrenarche, or the rise in adrenal androgens, developmentally corresponds to the period from birth until weaning in great apes and ancestral hominins. According to this hypothesis, humans achieved short IBIs by subdividing ancestral infancy into a nurseling phase, during which offspring fed at the breast, and a weanling phase, during which offspring fed specially prepared foods. Imprinted genes influence the timing of human weaning and adrenarche, with paternally expressed genes promoting delays in childhood maturation and maternally expressed genes promoting accelerated maturation. These observations suggest that the tempo of human development has been shaped by consequences for the fitness of kin, with faster development increasing maternal fitness at a cost to child fitness. The effects of imprinted genes suggest that the duration of the juvenile period (adrenarche until puberty) has also been shaped by evolutionary conflicts within the family.

Genomic Imprinting Is Implicated in the Psychology of Music.

Why do people sing to babies? Human infants are relatively altricial and need their parents' attention to survive. Infant-directed song may constitute a signal of that attention. In Prader-Willi syndrome (PWS), a rare disorder of genomic imprinting, genes from chromosome 15q11-q13 that are typically paternally expressed are unexpressed, which results in exaggeration of traits that reduce offspring's investment demands on the mother. PWS may thus be associated with a distinctive musical phenotype. We report unusual responses to music in people with PWS. Subjects with PWS ( N = 39) moved more during music listening, exhibited greater reductions in heart rate in response to music listening, and displayed a specific deficit in pitch-discrimination ability relative to typically developing adults and children ( N = 589). Paternally expressed genes from 15q11-q13, which are unexpressed in PWS, may thus increase demands for music and enhance perceptual sensitivity to music. These results implicate genomic imprinting in the psychology of music, informing theories of music's evolutionary history.

Impact of an oncology palliative care clinic on access to home care services.

Home care (HC) is important for patients with cancer as performance status declines. Our study of 1224 patients at a Canadian cancer center examined the impact of an oncology palliative care clinic (OPCC) on HC referral. The HC referral frequency was calculated before and after the first OPCC consultation, in total and according to performance status (Palliative Performance Scale, PPS). Characteristics associated with HC referral were investigated. After the first OPCC consultation, there was an increase in HC referral from 39% (477 of 1224; 49% of those with PPS ≤60) to 69% (841 of 1224; 88% of those with PPS ≤60). Factors independently associated with HC referral were poor PPS (P < .001) and older age (P = .003). Thus OPCC involvement resulted in markedly increased HC referrals, particularly for older patients with poor performance status.

The influence of media characters on children's food choices.

Two experiments were conducted to assess the role of media characters in influencing children's food choices; the first focused on children's self-reported preference, whereas the second focused on actual choice. The results of the experiments suggest that popular characters can make a difference in encouraging children to select one food over another. In the first experiment, children were more likely to indicate a preference for one food over another when one was associated with characters that they liked and with whom they were familiar. This effect was particularly strong when a sugary or salty snack branded by a favored character was competing with a healthier option branded by an unknown character or no character. Alternatively, when children were asked to choose between a healthy food and a sugary or salty snack, branding of the healthy food with a favored character did not significantly change appeal of that healthy snack. However, when foods within the same category (i.e., 2 vegetables, 2 fruits, or 2 grains) were asked to compete against each other, character branding strongly influenced children's food choice. Findings from the second experiment suggest that children are more willing to try more pieces of a healthy food if a favored character, in comparison with an unknown character, is promoting that food.

Exposure to 9/11 among youth and their mothers in New York City: enduring associations with mental health and sociopolitical attitudes.

The enduring impact of exposure to the 9/11 terrorist attacks on mental health and sociopolitical attitudes was examined in a sample of 427 adolescents (M = 16.20 years) and their mothers residing in New York City. Direct exposure to the terrorist attack was associated with youth depression symptoms and with mothers' posttraumatic stress disorder symptoms. There was no evidence of reciprocal effects of mother exposure on youth or of youth exposure on mothers. Although mothers reported engaging in more emotional processing coping assistance with their children, coping assistance was not associated with youth's symptomatology. Media exposure was found to be a strong predictor of youth's and mothers' sociopolitical attitudes about issues such as prejudice toward immigrants, social mistrust, and current events.