UC Davis

In humans and other pair-bonding species, mates form relatively long-lasting psychological attachments with each other that help them survive, reproduce, and rear offspring. This dissertation examined the biological, psychological, and evolutionary correlates of pair bonding and parenting (two primary types of attachment relationships) in both humans and titi monkeys.

In Chapter 1, I assessed whether romantic first impressions from initial interactions between potential partners (humans) predicted later relational outcomes (e.g., later romantic desire, contact attempts, direct messaging) using a design that could tease apart different possible mechanisms (e.g., mate value, selectivity, compatibility). Consistent with evolutionary models of human pair bonding, I found that, across three speed-dating studies (N = 559), mate value (average r = 0.22) and compatibility (average r = 0.15) were the best predictors of relationship-initiation, which indicates that these factors can have lingering effects on relationship development (even from the moment that two potential partners meet).

In Chapter 2, I assessed whether initial compatibility played a similar role in relationship development in titi monkeys (Plecturocebus cupreus) (n = 12), a socially monogamous and biparental nonhuman primate species. To do this, I developed a “monkey speed-dating test” to assess subjects’ initial preferences for different potential mates, and then paired subjects according to compatibility. Consistent with the results of Chapter 1, I found that, on average, the six speed-dating pairs exhibited higher levels of affiliative Tail Twining (β = 0.31) compared to a group of 13 age-matched comparison pairs. I also found that the degree of initial compatibility within speed-dating pairs predicted higher levels of Combined Affiliation at earlier post-pairing time points (with the association peaking at 2 months post-pairing, β = 0.57), which suggests that initial compatibility acted as a catalyst for pair bonding.

In Chapter 3, I investigated the neuroendocrine correlates of the parent-offspring bond in titi monkeys across a set of three studies. In Studies 1-2, I used receptor autoradiography to correlate vasopressin receptor 1a (AVPR1a) binding in the hippocampus (Study 1, n = 10) and the rest of the forebrain (Study 2, n = 23) with parental status, parental experience, parity, infant carrying, and pair affiliation. I found that parents exhibited lower AVPR1a binding than non-parents throughout most brain regions assessed, with especially strong effects in the hippocampus (β = -0.61), superior colliculus (β = -0.88), lateral septum (β = -0.35), and medial preoptic area (β = -0.29). In Study 3 (n = 44), I compared pre- and postpartum urinary androgen levels in parents and non-parents and found that mothers exhibited a sustained androgen decrease across 3-4 months postpartum (relative to 3 months prepartum; β ranged from -0.72 to -0.62 for different comparisons). For males, multiparous fathers exhibited decreased androgen levels at 1-2 weeks postpartum (β = -0.25) and at 3-4 months postpartum (β = -0.40) compared to the prepartum, indicating both immediate and long-term reductions with subsequent paternal experience. Together, these results suggest that decreases in AVPR1a binding and circulating androgens are associated with parental behavior and physiology in titi monkeys.

The primary results for each study are presented in each dissertation chapter. For information about secondary analyses that were performed in each chapter, see the Supplementary Information files for each respective chapter.