Biological Psychology 94 (2013) 152–159 Contents lists available at SciVerse ScienceDirect Biological Psychology journa l h om epa ge: www.elsevier.com/locate/biopsycho Postnatal testosterone levels and disorder relevant behavior in the second year of life Janet Saenz ∗ , Gerianne M. Alexander Department of Psychology, Texas A&M University, College Station, TX 77843, United States a r t i c l e i n f o Article history: Received 14 February 2013 Accepted 14 May 2013 Available online 28 May 2013 Keywords: Postnatal androgens Testosterone Social–emotional problems Sex differences a b s t r a c t The objective of the current study was to investigate the relationship between testosterone collected at 3–4 months of age and sex-linked disorder-relevant behaviors in the second year of life. Eighty-four children participated at 3–4 (when salivary testosterone levels were obtained and second to fourth digit ratios were measured) and 18–24 months of age (when behavioral ratings of aggression and verbal ability were coded from two 8-min play sessions). Parents also completed the Brief Infant–Toddler Social and Emotional Assessment, and the four subscales (Internalizing, Externalizing, Dysregulation, and Autism Spectrum Disorder) were used to indicate child specific problems. Greater postnatal testosterone levels in early infancy were predictive of more male-typical behaviors in the second year of life (i.e., more autism spectrum behaviors, less time vocalizing, and more Internalizing Problems). These results support the hypothesis that early infancy may be another critical period for the development of gender-linked behavior. Published by Elsevier B.V. 1. Introduction Experimental research on non-human species has demon- strated that higher prenatal androgens in males compared to females masculinize the genitalia, the developing neural system, and behavior (Breedlove, Cooke, & Jordan, 1999; Hines, 2002, 2004). Compelling evidence for similar effects of prenatal testosterone on human behavior comes from “experiments of nature”, research that compares behavior of healthy individuals to that of those with endocrine disorders, such as congenital adrenal hyperpla- sia (CAH). Congenital adrenal hyperplasia, an autosomal recessive disorder, disrupts the adrenal glands’ ability to produce the hor- mone cortisol (Merke & Camacho, 2001). As a consequence of the resulting hyper-stimulation of the adrenal gland, girls with CAH are exposed to elevated levels of prenatal androgens (Pang et al., 1980). Consistent with the role of androgens in the development of gender-linked behavior, compared to unaffected siblings girls with CAH exhibit more male-typical behavior, including increased aggression (Berenbaum & Resnick, 1997; Pasterski et al., 2007), increased male-typical toy preferences (Berenbaum & Hines, 1992; Pasterski et al., 2005), stronger preferences for boys as playmates (Hines & Kaufman, 1994), lower rates of exclusive heterosexual ∗ Corresponding author at: Department of Psychology, Texas A&M University, MS 4235, College Station, TX 77843, United States. Tel.: +1 979 845 0231; fax: +1 979 845 4727. E-mail address: jsaenz@neo.tamu.edu (J. Saenz). fantasy (Zucker et al., 1996), and less interest in infants (Leveroni & Berenbaum, 1998). Research using digit ratios, a putative proxy measure of prenatal androgen–estrogen action, also supports the masculinizing effects of higher prenatal androgen levels (Hönekopp, Bartholdt, Beler, & Liebert, 2007). Digit ratios are a ratio of the length of the index finger over the length of the ring finger, such that smaller ratios or a shorter index finger relative to ring finger are thought to be indicators of more prenatal androgen action (Lutchmaya, Baron- Cohen, Raggatt, Knickmeyer, & Manning, 2004; Manning, Bundred, Newton, & Flanagan, 2003). Although this method has been con- troversial (Berenbaum, Bryk, Nowak, Quigley, & Moffat, 2009), the ratios of testosterone to estradiol measured in amniocentesis sam- ples have correlated with a child’s subsequent digit ratios at the age of 2-years (Lutchmaya et al., 2004). Research has also shown that women with CAH, who are exposed to abnormally high levels of prenatal androgens, generally have smaller (more masculine) digit ratios (Brown, Hines, Fane, & Breedlove, 2002; Okten, Kalyoncu, & Yaris, 2002), yet some studies report no difference in digit ratios of women with CAH and healthy controls (Buck, Williams, Hughes, & Acerini, 2003). Smaller, more masculine, digit ratios have also been associated with male-typical play behavior in preschool boys (Hönekopp & Thierfelder, 2009), greater fine motor control and motion detection in children with an ASD (Milne et al., 2006), low agreeableness and verbal intelligence in adults (Luxen & Buunk, 2005), increased physical aggression in men (Bailey & Hurd, 2005), increased reactive aggression in women (Benderlioglu & Nelson, 2004), and increased sexual experience and fantasy for non-strictly heterosexual women (Anders & Hampson, 2005). 0301-0511/$ – see front matter. Published by Elsevier B.V. http://dx.doi.org/10.1016/j.biopsycho.2013.05.011