Homosexuality, the natural choice? (Gay Animals are Common)

berberry writes:It might be nature's own check on over-population.

Homosexuality in men and number of older brothers
R Blanchard and AF Bogaert
Clarke Institute of Psychiatry, Toronto, Ontario, Canada.OBJECTIVE: This study investigated whether homosexual men have a higher mean birth order than heterosexual men primarily because they have more older brothers or because they have more older siblings of both sexes. METHOD: For the main analyses, 302 heterosexual men were individually matched on year of birth with an equal number of heterosexual men. Each completed a self-administered, anonymous questionnaire concerning family background and other biodemographic information. RESULTS: Logistic regression analysis showed that homosexuality was positively correlated with the proband's number of older brothers but not with older sisters, younger brothers, younger sisters, or parental age at the time of the proband's birth. Each additional older brother increased the odds of homosexuality by 33%. CONCLUSIONS: These results restrict the range of possible theories of the birth order phenomenon to those that can explain not only why older brothers increase the probability of homosexuality in later-born males but also why older sisters neither enhance this effect nor counteract it.

Homosexuality, birth order, and evolution: Toward an equilibrium reproductive economics of homosexuality
Miller EM
ARCHIVES OF SEXUAL BEHAVIOR
29 (1): 1-34 FEB 2000Abstract:
The survival of a human predisposition for homosexuality can be explained by sexual orientation being a polygenetic trait that is influenced by a number of genes. During development these shift male brain development in the female direction. Inheritance of several such alleles produces homosexuality. Single alleles make for greater sensitivity, empathy, tendermindedness, and kindness. These traits make heterosexual carriers of the genes better fathers and more attractive mates. There is a balanced polymorphism in which the feminizing effect of these alleles in heterosexuals offsets the adverse effects (on reproductive success) of these alleles' contribution to homosexuality. A similar effect probably occurs for genes that can produce lesbianism in females. The whole system survives because it serves to provide a high degree of variability among the personalities of offspring, providing the genotype with diversification and reducing competition among offspring for the same niches. An allele with a large effect can survive in these circumstances in males, but it is less likely to survive in females. The birth order effect on homosexuality is probably a by-product of a biological mechanism that shifts personalities more in the feminine direction in the later born sons, reducing the probability of these sons engaging in unproductive competition with each other.

The relation between sexual orientation and penile size
Bogaert AF, Hershberger S
ARCHIVES OF SEXUAL BEHAVIOR
28 (3): 213-221 JUN 1999Abstract:
The relation between sexual orientation and penile dimensions in a large sample of men was studied. Subjects were 5122 men interviewed by the Kinsey Institute for Research in Sex, Gender and Reproduction from 1938 to 1963. They were dichotomously classified as either homosexual (n = 935) or heterosexual (n = 4187). Penile dimensions were assessed using five measures of penile length and circumference from Kinsey's original protocol. On all Jive measures, homosexual men reported larger penises than did heterosexual men. Explanations for these differences are discussed, including the possibility that these findings provide additional evidence that variations in prenatal hormonal levels (or other biological mechanisms affecting reproductive structures) affect sexual orientation development.