This dissertation research tested a model predicting that human fathers invest in offspring in patterns that vary as a function of information assayed from a father's own early environment (e.g., cues indicating environmental harshness and/or unpredictability during a father's early development). Human fathers exhibit plasticity with regard to the level of investment provided to offspring. The endocrine substrates that have evolved to support these facultative paternal responses to environmental conditions should also demonstrate similar (and closely aligned) variation from one ecological context to the next. The nature of the specific ecological cues that a father's endocrine and behavioral systems rely on for developmental calibration has not been entirely elucidated. This study provided a test of the level of paternal investment in a newborn infant's life, based on a father's own early life experience with environmental harshness and instability and the degree to which a father's neuroendocrine system (i.e., testosterone) responds to the birth of his child.

Our research team conducted three home visits that were scheduled across a 9-10 month period: Time 1 was in the late third trimester of pregnancy, Time 2 was three months following the birth of the child, and Time 3 took place when the infant was 9-10 months old. We recruited 226 two-parent, first-birth families. Participants provided self-report measures of early life experiences: i.e., scales designed to measure early SES and exposure to trauma. At each visit, participants also provided two saliva samples (AM and PM) at each collection period to be assayed for testosterone. Lastly, we measured investment in two ways: (1) an Experience Sampling Method administered survey that measured the quantity of time fathers spent with their infants; (2) a measure of paternal quality of care---infants (9-10 months) old were exposed to novel stimuli intended to elicit a fear response. Videos of paternal behaviors were coded by independent raters (for quality of care, e.g., warmth, support).

While we did see significant variation between fathers in the quantity of time they reported interacting with their infants, the level of trauma experienced in childhood or a father's own childhood SES could not account for this variance. When measuring paternal investment quality however, early childhood experience influenced how fathers interacted with their infants during the stimuli exercise. Fathers who reported being raised in low SES environments and who experienced trauma in childhood displayed lower levels of quality care. Levels of testosterone (on average) decreased from Time 1 to Time 2. We detected significant individual variation between males in (1) their baseline level of testosterone prior to childbirth; (2) the slope of their testosterone response to childbirth; and (3) the slope of their testosterone's ascent back to baseline levels. However, neither childhood SES nor trauma could account for this variability. We did detect (non-significant statistical trends) that the degree (i.e., slope) to which testosterone recovered from Time 2 to Time 3 was related to paternal investment of both time and investment quality. Fathers who had a higher slope of recovery demonstrated decreased levels of investment quality and quantity.