Hormonal correlates of human paternal interactions: A hospital-based investigation in urban Jamaica P.B. Gray a, ⁎ , J.C. Parkin a , M.E. Samms-Vaughan b a Department of Anthropology and Ethnic Studies, 4505 Maryland Parkway #5003, University of Nevada, Las Vegas, Las Vegas, NV, USA b Section of Child Health, University of the West Indies, Mona, Jamaica Received 11 May 2007; revised 8 July 2007; accepted 16 July 2007 Available online 24 July 2007 Abstract To expand our understanding of the neuroendocrine mechanisms underlying human fatherhood, including its cross-cultural expression, we investigated the hormonal correlates of fatherhood in the greater Kingston, Jamaica area. We recruited 43 men, aged 18–38, to participate: 15 single men; 16 “coresidential” fathers (men who live with their adult female partner and youngest child); and 12 “visiting” fathers (men who live apart from their adult female partner and youngest child). The research protocol entailed biological sampling before and after a 20-min behavioral session during which single men sat alone and fathers interacted with their partner and youngest child. Hormone measures relied upon minimally invasive techniques (salivary testosterone and cortisol, finger prick blood spot prolactin, urinary oxytocin and vasopressin). Results revealed significant group differences in average male testosterone levels ( p = 0.006), with post hoc contrasts indicating that visiting fathers had significantly ( p b 0.05) lower testosterone levels than single men. Prolactin profiles also differed significantly across groups ( p = 0.010) whereby post hoc contrasts showed that prolactin levels of single men declined significantly compared with the flat levels of visiting fathers ( p b 0.05). No group differences in cortisol, oxytocin or vasopressin levels were observed. However, among fathers, vasopressin levels were significantly and negatively (r = - .431, p = 0.022) correlated with the age of a man's youngest child. These results thus implicate lower testosterone levels as well as prolactin and vasopressin in human fatherhood. These findings also highlight the importance of sociocultural context in human fatherhood while exhibiting parallels with existing data on the non-human vertebrate hormonal bases of paternal care. © 2007 Elsevier Inc. All rights reserved. Keywords: Paternal care; Caribbean; Cross-cultural; Testosterone; Prolactin; Vasopressin Introduction Humans are among the approximately 5% of mammalian species that provide paternal care (Clutton-Brock, 1991; Kleiman, 1977; Reichard and Boesch, 2003; Whitten, 1987). Evolutionary models recognize that human paternal care appears linked to pair bonds between mates and long periods of offspring dependency in complex multi-male, multi-female groups (Flinn, 2006; Hrdy, 1999; Kaplan and Lancaster, 2003). Most evolutionary models suggest that human paternal care arose among our Homo ancestors within approximately the past 2.5 million years (Dixson, 1998; Geary and Flinn, 2001; Hewlett, 1992; Lancaster and Lancaster, 1987; McHenry, 1996). However, evolutionary models differ in the degree to which they emphasize the importance of direct (e.g., holding, carrying) care compared with indirect (e.g., food provisioning) care. Human paternal care also exhibits cross- cultural and historical variation (Barry and Paxson, 1971; Eibl- Eibsfeldt, 1989; Hewlett, 1992; Marlowe, 2000). Variation in human paternal care is responsive to a host of variables (Geary, 2000) including the mode of subsistence (Hewlett, 2004; Marlowe, 2000) and the nature of a man's relationship to a child's mother (Parke, 1996; Whiting and Whiting, 1975). Here, we build on this evolutionary and cross-cultural back- ground to investigate human fatherhood in an African Caribbean context. In African Caribbean countries, children are commonly born into dynamic family structures characterized by a variable paternal role and important maternal kin assistance (Barrow, 1996; Madrigal, 2006; Roopnarine et al., 2005; Smith, 1996). Births commonly take place during so-called visiting relationships, in Hormones and Behavior 52 (2007) 499 – 507 www.elsevier.com/locate/yhbeh ⁎ Corresponding author. E-mail address: peter.gray@unlv.edu (P.B. Gray). 0018-506X/$ - see front matter © 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.yhbeh.2007.07.005