James Brody
July 5th, 2006, 01:40 PM
"The most consistent biodemographic correlate of sexual orientation in men is the number of older brothers (fraternal birth order). The mechanism underlying this effect remains unknown. In this article, I provide a direct test pitting prenatal against postnatal (e.g., social rearing) mechanisms. Four samples of homosexual and heterosexual men (total n 944), including one sample of men raised in nonbiological and blended families (e.g., raised with half or step-siblings or as adoptees) were studied. Only biological older brothers, and not any other sibling characteristic, including nonbiological older brothers, predicted men' sexual orientation, regardless of the amount of time reared with these siblings. These results strongly suggest a prenatal origin to the fraternal birth order effect."
The talk shows buzz with these data but they have been available for some time.
(From Brody, 2005) "Hrdy (1999) describes vitality, plumpness, hairiness, and even a close resemblance to the father as means to pass the first inspections that human mothers make in different cultures. Sons, however, are more variable than daughters for a staggering range of characteristics (Miller, 2000; Pinker, 2002) and bear the greater focus of maternal scrutiny (Trivers, 1972).
"- More human males are conceived than delivered (1.6-1.2/1 vs. 1.05/1, Spreen, Risser & Edgell ,1995) sometimes due to allergic reactions between mother and her son (Spreen et al, 1995). Infants that pass maternal physiological standards are carried to full term and have fewer developmental impairments, less impulsive behavior, and higher IQs (Spreen et al, 1995).
"- Human mothers abort children or put them up for adoption in relation to paternal fitness and investment, and economic conditions (Hrdy, 1999) but they abort sons more than daughters in drought, famine, or changes in maternal social dominance (Kruuk, Clutton-Brock, Albon, Pemberton, & Guinness, 1999).
"There are other signs of how much males cost for females. In one preindustrial society, a daughter lengthens the mother's life by an average of 23 weeks, a son shortens it by an average of 34 (Helle, Lummaa, & Jokela. 2002). In other studies, sons have more problems at delivery apart from their larger size (Lieberman, Lang, Cohen, Frigoletto, Acker, & Rao, 1997), often require longer gestation (Divon, Ferber, Nissell, & Westgren, 2003), sometimes trigger immune reactions in mothers (Blanchard, 2001; Spreen et al, 1995) and have higher rates of infant mortality (Spreen et al, 1995). More sons are born in the spring (Cagnacci, Renzi, Arangino, Alessandrini, & Volpe, 2003) and usually to younger mothers (Trivers & Willard, 1973). A series of brothers often predicts that the youngest will have greater fluctuating asymmetry (Lalumière, Harris, & Rice, 1999), a greater risk for being homosexual (Blanchard, 2001; Cohen, 1999), and some greater risk for psychopathology (Herrell, Goldberg, True, Ramakrishnan, Lyons, Eisen, & Tsuang, 1999; Fergusson, Horwood, & Beautrais,1999). Small males at birth are less likely to marry (Phillips, Handelsman, Eriksson, Forsen, Osmond, & Barker, 2001). Further, children with physical defects are more likely targets for institutionalization and abandonment (Buss, 1999) or parental abuse and infanticide (Daly & Wilson, 1981; 1988). We, again, expect males to show the greater numbers of defects and to die earlier."
References:
Bogaert, AF (2006) Biological versus nonbiological older brothers
and men' sexual orientation. PNAS 103(28): 10771?10774, www.pnas.org /cgi/doi /10.1073/ pnas.0511152103
Brody, J.F. (2001) Sexual selection: Mind Your Mothers. Poster presentation at the Human Behavior and Evolution Society annual meeting, London.
Brody, J. (2005) ADHD: Inhibition, Emergent Networks, and Maternal Investment. Chapter 2 in Michelle Larimer (Ed.) Attention Deficit Hyperactivity Disorder (ADHD) Research. Hauppage, NY: Nova Science Biomedical Series. pp.19-58.
The talk shows buzz with these data but they have been available for some time.
(From Brody, 2005) "Hrdy (1999) describes vitality, plumpness, hairiness, and even a close resemblance to the father as means to pass the first inspections that human mothers make in different cultures. Sons, however, are more variable than daughters for a staggering range of characteristics (Miller, 2000; Pinker, 2002) and bear the greater focus of maternal scrutiny (Trivers, 1972).
"- More human males are conceived than delivered (1.6-1.2/1 vs. 1.05/1, Spreen, Risser & Edgell ,1995) sometimes due to allergic reactions between mother and her son (Spreen et al, 1995). Infants that pass maternal physiological standards are carried to full term and have fewer developmental impairments, less impulsive behavior, and higher IQs (Spreen et al, 1995).
"- Human mothers abort children or put them up for adoption in relation to paternal fitness and investment, and economic conditions (Hrdy, 1999) but they abort sons more than daughters in drought, famine, or changes in maternal social dominance (Kruuk, Clutton-Brock, Albon, Pemberton, & Guinness, 1999).
"There are other signs of how much males cost for females. In one preindustrial society, a daughter lengthens the mother's life by an average of 23 weeks, a son shortens it by an average of 34 (Helle, Lummaa, & Jokela. 2002). In other studies, sons have more problems at delivery apart from their larger size (Lieberman, Lang, Cohen, Frigoletto, Acker, & Rao, 1997), often require longer gestation (Divon, Ferber, Nissell, & Westgren, 2003), sometimes trigger immune reactions in mothers (Blanchard, 2001; Spreen et al, 1995) and have higher rates of infant mortality (Spreen et al, 1995). More sons are born in the spring (Cagnacci, Renzi, Arangino, Alessandrini, & Volpe, 2003) and usually to younger mothers (Trivers & Willard, 1973). A series of brothers often predicts that the youngest will have greater fluctuating asymmetry (Lalumière, Harris, & Rice, 1999), a greater risk for being homosexual (Blanchard, 2001; Cohen, 1999), and some greater risk for psychopathology (Herrell, Goldberg, True, Ramakrishnan, Lyons, Eisen, & Tsuang, 1999; Fergusson, Horwood, & Beautrais,1999). Small males at birth are less likely to marry (Phillips, Handelsman, Eriksson, Forsen, Osmond, & Barker, 2001). Further, children with physical defects are more likely targets for institutionalization and abandonment (Buss, 1999) or parental abuse and infanticide (Daly & Wilson, 1981; 1988). We, again, expect males to show the greater numbers of defects and to die earlier."
References:
Bogaert, AF (2006) Biological versus nonbiological older brothers
and men' sexual orientation. PNAS 103(28): 10771?10774, www.pnas.org /cgi/doi /10.1073/ pnas.0511152103
Brody, J.F. (2001) Sexual selection: Mind Your Mothers. Poster presentation at the Human Behavior and Evolution Society annual meeting, London.
Brody, J. (2005) ADHD: Inhibition, Emergent Networks, and Maternal Investment. Chapter 2 in Michelle Larimer (Ed.) Attention Deficit Hyperactivity Disorder (ADHD) Research. Hauppage, NY: Nova Science Biomedical Series. pp.19-58.