R. Nathan Pipitone

Bottle feeding simulates child loss: postpartum depression and evolutionary medicine.

At the level of a mothers basic biology, the decision to bottle feed unwittingly mimics conditions associated with the death of an infant. Child loss is a well documented trigger for depression particularly in mothers, and growing evidence shows that bottle feeding is a risk factor for postpartum depression. The implications of this hypothesis for infant feeding practices, hospital procedures that lead to intermittent separation between mothers and infants during the immediate postpartum period, parallels between an increased desire to hold infants by mothers who bottle feed and responses to infant death among nonhuman primates, and the relationship between weaning and depression are discussed in the context of an emerging discipline known as evolutionary medicine.

Voice and handgrip strength predict reproductive success in a group of indigenous African females.

Evolutionary accounts of human traits are often based on proxies for genetic fitness (e.g., number of sex partners, facial attractiveness). Instead of using proxies, actual differences in reproductive success is a more direct measure of Darwinian fitness. Certain voice acoustics such as fundamental frequency and measures of health such as handgrip strength correlate with proxies of fitness, yet there are few studies showing the relation of these traits to reproduction. Here, we explore whether the fundamental frequency of the voice and handgrip strength account for differences in actual reproduction among a population of natural fertility humans. Our results show that both fundamental frequency and handgrip strength predict several measures of reproductive success among a group of indigenous Namibian females, particularly amongst the elderly, with weight also predicting reproductive outcomes among males. These findings demonstrate that both hormonally regulated and phenotypic quality markers can be used as measures of Darwinian fitness among humans living under conditions that resemble the evolutionary environment of Homo sapiens. We also argue that these findings provide support for the Grandmother Hypothesis.

Morphology and Behavior : Phrenology Revisited

Research conducted by evolutionary psychologists and biologists shows that subtle individual differences in body morphology can be related to surprising and important differences in human behavior and reproductive success. The authors summarize recent work on these effects as they relate to fluctuating asymmetry, facial attractiveness, finger digit morphology, sexually dimorphic differences in body configuration, and head circumference. Examples include the discovery that women who have sex with bilaterally symmetrical men report more orgasms; men with attractive faces have higher quality sperm; the length of the index finger in relation to the ring finger is related to verbal fluency, spatial ability, and the risk of autism; women with an hourglass figure have more regular menstrual cycles and are more fertile; and the sound of a person’s voice predicts his or her sexual behavior.

Physiological changes in response to hearing female voices recorded at high fertility

The human voice transmits pertinent information regarding health status and age, with recent evidence suggesting that it plays an important role in mate selection. However, the mechanism that drives preferences for voices of fertile females has yet to be elucidated. The current study examined the physiological changes that occur when listening to voices recorded from naturally cycling females at high and low fertility phases of the menstrual cycle, as well as from females using hormonal contraception. We found the voices of naturally cycling females recorded during a high fertility phase were rated as more attractive and produced the greatest increase in galvanic skin response (GSR). Heart rate (HR) also showed a trend towards the highest increase when listening to naturally cycling, high fertility female voices. There were no differences in ratings of voice attractiveness, GSR, or HR between the voices recorded from females using hormonal contraception. Analyzed separately, male and female listeners both showed a preference for naturally cycling, high fertility voices. Female listeners additionally showed increased GSR and HR responses to naturally cycling, high fertility voices. We discuss the adaptive benefits of detecting vocal changes for male as well as female listeners, and also discuss the role that the nervous system plays during human mate assessments.