Sex Differences in Early Infancy

Abstract

Sex‐linked behaviors in infancy have generated a great deal of interest, in part because they offer a way of assessing the extent to which sexually dimorphic behaviors exist before extensive social and educational experiences. This article reviews sex differences in basic and sensory processes, social behavior, and cognitive behavior that have been reported during the 1st year of life, and discusses current knowledge about the underlying basis for these differences and the extent to which they contribute to later behavior. Careful investigation of the interaction between social and biological factors in infancy will be necessary to fully understand the nature and development of human sex differences.

The Evolution of Culturally-Variable Sex Differences: Men and Women Are Not Always Different, but When They Are…It Appears Not to Result from Patriarchy or Sex Role Socialization

“…Further support of neuroandrogenic theory includes findings that girls with gene variants that make them more sensitive to testosterone develop more masculine personalities (with especially strong effects among those girls whose mothers tried the hardest to socialize their daughters to (Hare et al 2009;Schneider et al 2006). In short, the seeds of many psychological sex differences appear to be sewn before birth, with future developmental experiences being shaped by the degree of prenatal neuroandrogenic brain masculinization (Alexander and Wilcox 2012). Some psychological sex differences are not established before birth, of course, and instead result from activational effects that emerge in early childhood (Del Giudice and Belsky 2010;Ellis 2004) or at puberty (Galambos et al 2009;Hyde et al 2008;Ruigrok et al 2013).…”

Sex, Age, and Cognitive Correlates of Asymmetries in Thickness of the Cortical Mantle Across the Life Span

“…The left Ͼ right CT asymmetry we detected as a main effect in anterior brain regions was significantly more prominent in females, whereas the right Ͼ left asymmetry in posterior brain regions was more prominent in males. These sex differences may represent the neuroanatomical correlates of the most robust and best replicated differences in cognitive abilities across sexes, a female advantage on verbal tasks (Kimura and Clarke, 2002) and a male advantage on visuospatial tasks (Hines, 2011;Alexander and Wilcox, 2012). Functional imaging studies have shown that language functions involve anterior brain regions most prominently (Binder and Price, 2001) and visuospatial functions involve posterior brain regions most prominently (Hugdahl et al, 2006), consistent with the exaggerated cortical asymmetries we identified in females in anterior brain regions and in males in posterior brain regions.…”

Empathy: Gender effects in brain and behavior

“…For example, from birth, there appear to be sex differences in social behaviors (for a review, see Alexander and Wilcox, 2012), including potential precursors of empathic predisposition (McClure, 2000). Female neonates, compared to males, are more likely to cry and cry longer when hearing another infant cry (Hoffman, 1977; Sagi and Hoffman, 1976; Simner, 1971).…”

“…However, meta-analyses examining gender and sex differences in empathy provide results supporting fairly stable gender differences across a broad range of measures (e.g., Cohn, 1991; Eisenberg and Lennon, 1983; Feingold, 1994; Hall, 1978, 1984; Hoffman, 1977; O’Brien et al, 2013; Thompson and Voyer, 2014; although, for null results see Lamm et al, 2007). Additionally, empathy has developmental precursors in early infancy (Alexander and Wilcox, 2012; McClure, 2000) as well as evolutionary precursors in other social animals (Preston and De Waal, 2002). Indeed, there is considerable overlap between empathetic behaviors demonstrated in young humans early in development and in nonhuman animals.…”