first born son, to 4% for the second, 6% for the third and so on. Scientists have estimated between 15% and 29% of gay men may owe their sexual orientation to this effect, but the number may be higher, as prior miscarriages and terminations of male pregnancies may have exposed their mothers to Y-linked antigens. The fraternal birth order effect would not likely apply to first born gay sons; instead, scientists say they may owe their orientation to genes, prenatal hormones and other maternal immune responses which also influence brain development. This effect is nullified if the man is left-handed. Ray Blanchard and Anthony Bogaert are credited with discovering the effect in the 1990s. J. Michael Bailey and Jacques Balthazart say the FBO effect demonstrates that sexual orientation is heavily influenced by prenatal biological mechanisms rather than unidentified factors in socialization. Environmental factors In the field of genetics, any factor which is non-genetic is considered an environmental influence. However, environmental influence does not automatically imply that the social environment influences or contributes to the development of sexual orientation. There is a vast non-social environment that is non-genetic yet still biological, such as prenatal development, that likely helps shape sexual orientation. Social factors There is no substantive evidence to support the suggestion that early childhood experiences, parenting, sexual abuse, or other adverse life events influence sexual orientation. Hypotheses for the impact of the post-natal social environment on sexual orientation are weak, especially for males. Parental attitudes may affect whether or not children openly identify with their sexual orientation. Though it has since been found to be based on prejudice and misinformation, it was once thought that homosexuality was the result of faulty psychological development, resulting from childhood experiences and troubled relationships, including childhood sexual abuse. Such hypotheses "have been associated with highly charged political, moral and theological grounds for wanting to believe that it can". Influences: professional organizations' statements The American Academy of Pediatrics in 2004 stated: The American Psychological Association, the American Psychiatric Association, and the National Association of Social Workers in 2006 stated: The Royal College of Psychiatrists in 2007 stated: The American Psychiatric Association stated in 2011: A legal brief dated September 26, 2007, and presented on behalf of the American Psychological Association, California Psychological Association, American Psychiatric Association, National Association of Social Workers, and National Association of Social Workers, California Chapter, stated: Efforts to change sexual orientation