From Evolution & Human Behavior Volume 33, Issue 4 , Pages 357-364, July 2012
Title: “Low serum vitamin A mothers breastfeed daughters more often than sons in drought-ridden northern Kenya: a test of the Trivers–Willard hypothesis”
Abstract: “The Trivers–Willard hypothesis predicts that natural selection should favor unequal parental investment between daughters and sons based upon maternal condition and offspring reproductive potential. Specifically, it predicts that mothers in good condition should increase investment toward sons, while mothers in poor condition should favor daughters. Previous tests of the hypothesis in human populations overwhelmingly focused on economic resources as maternal condition indicators. We test the Trivers–Willard hypothesis using maternal nutrition—energy and vitamin A status representing macro- and micronutrition, respectively—as the indicator for maternal condition, with breastfeeding frequency recalls serving as the indicator for parental investment. Data from exclusively breastfeeding mothers (n=83) in drought-ridden Ariaal agropastoral villages of northern Kenya were used to test the hypothesis that mothers in poor condition will breastfeed daughters more frequently than sons. Poor condition was defined as having a body mass index <18.5 or serum retinol (vitamin A) concentration <1.05 µmol/l. A linear regression model was applied using breastfeeding frequency as the dependent variable and respective maternal condition, infant’s sex, and the maternal condition–infant’s sex interaction as the predictors, controlling for covariates. Results supported the hypothesis only in the vitamin A model which predicts that low-vitamin-A mothers breastfeed daughters significantly more frequently than sons (11 vs. 6 times/day), while vitamin-A-sufficient mothers breastfeed daughters and sons equivalently (9 times). These results indicate that maternal nutritional status, particularly micronutrient status, can contribute to the investigation of the evolutionary hypothesis of sex-biased parental investment.”
Basically, poor low status women invest more in their girls and richer high status women invest more in their boys. Maybe it is related to the high failure of boys, compared to girls, in low status families.
From: Evolution & Human Behavior Volume 33, Issue 4 , Pages 268-273, July 2012
Title: “Low nonpaternity rate in an old Afrikaner family”
Abstract: “Extrapair paternity is a crucial parameter for evolutionary explanations of reproductive behavior. Early studies and human testis size suggest that human males secure/suffer frequent extrapair paternity. If these high rates are indeed true, it brings into question studies that use genealogies to infer human life history and the history of diseases since the recorded genealogies do not reflect paths of genetic inheritance. We measure the rate of nonpaternity in an old Afrikaner family in South Africa by comparing Y-chromosome short tandem repeats to the genealogy of males. In this population, the nonpaternity rate was 0.73%. This low rate is observed in other studies that matched genealogies to genetic markers and more recent studies that also find estimates below 1%. It may be that imposed religious morals have led to reduced extrapair activities in some historic populations. We also found that the mutation rate is high for this family, but is unrelated to age at conception.”
They had cuckolding rate of 0.73%, before the pill/abortion/or the fear of paternity tests. This is quite amazing considering to order of magnitude greater cuckolding rate of ~5% to 10% common today. Religion helps prevent cuckolding, which gives men more paternity certainty, which makes it worthwhile for them to invest in the children… God might be a lie, but religion is one of the strongest tools to shape healthy human societies.
(For the new reader, here is a link to the latest draft (pdf, 14/Jun/2012) of the Guide for a Young Patriarch which is based on the posts made in this blog and attempts to organize them into a consistent message.)