Notes: Kinship, Parental Care, and Concealed Ovulation

Overview and Core Argument

• Central theme: Interaction of kinship, parental care, and human social structure in shaping reproductive strategies and life-history outcomes.

• Alexander and Noonan (1979) proposed that "concealment of ovulation" evolved as a driver of human social evolution.

  • It supports "paternal care," which increases offspring success by maintaining paternity certainty.

  • Ovulatory advertisement has two costs to males: attracting rivals and enabling females to seek other mates who would compete for paternal care.

• Strassmann's fieldwork (Dogon of Mali) and broader evidence highlight "dual mating strategies, menstrual cycles, and cultural practices" (e.g., menstrual huts) in managing paternity and paternal investment.

Paternal Care and Offspring Outcomes

• "Paternal care" is strongly linked to offspring survival and social success.

  • Ache children without fathers are $3.9$ times more likely to be killed annually.

  • Children of divorced parents are $2.8$ times more likely to be killed.

  • Paternal presence influences social development, such as earlier initiation ages for Martu aborigines.

Concealed Ovulation: Debate and Evidence

• "Concealment of ovulation" refers to "reduced conspicuousness" in humans, not total invisibility.

• Even with modern knowledge, self-reported ovulation cues are unreliable for most women.

  • Accuracy is about $28\%$ without basal body temperature.

  • Accuracy rises to $36.1\%$ with basal body temperature included.

• This unreliability supports the idea that overt estrus is uncommon in humans.

Dogon Fieldwork and Mating Strategies

• Dogon women experience roughly $100$ menses per lifetime compared to $400$ in North American women, spending more time pregnant or lactating.

• Low "extra-pair paternity (EPP) rate" of $1.8\%$ among the Dogon (N = $1704$ father–offspring pairs), suggesting EPCs are rare during the fertile period.

• "Menstrual huts" and shading shelters are cultural mechanisms for monitoring menstruation, supporting male enforcement of taboos to reduce cuckoldry risk.

• This supports a "combo hypothesis" where female EPCs are limited and strategically timed with paternal investment, leading to relatively high paternity certainty.

Sperm Competition and Primate Mating Systems

• Comparative data on sperm production and testes size indicate weaker postcopulatory sexual selection in humans.

• Human testes mass to body mass ratio (T/B) is $0.06$, similar to orangutans ($0.05$) but much lower than chimpanzees ($0.27$).

• This relatively modest ratio suggests less intense sperm competition.

Skepticism Regarding Strong Human Estrus Cues

• Five key reasons for skepticism about strong human estrus/ovulatory cues:

  1. High paternal investment is inconsistent with high cuckoldry risk.

  2. Genetic studies show relatively high paternity certainty.

  3. Primate morphological and physiological comparisons do not support strong postcopulatory selection.

  4. Ethnographic/demographic data indicate ovulation concealment across populations.

  5. The mechanistic basis for strong ovulatory cues remains unidentified.

Synthesis and Conclusion

• "Concealed ovulation, paternal care, and kinship patterns" form an integrated suite of traits that shaped human social evolution.

• Cultural practices reinforce biological strategies to optimize paternal investment.