It points strongly to a biological origin for our sexualities. The Growth of Biological Thought: Another issue is the finding that even monozygotic twins can be different and there is a mechanism which might account for monozygotic twins being discordant for homosexuality. Three gene finding studies showed that gay brothers share genetic markers on the X chromosome; the most recent study also found shared markers on chromosome 8. If one is gay, the other is gay about 50 per cent of…. So showing evidence of change is not an argument against biology.
One explanation for these differences is the idea that differential exposure to hormone levels in the womb during fetal development may change the masculinization of the brain in homosexual men.
Biology and sexual orientation
The "gay uncle hypothesis" posits that people who themselves do not have children may nonetheless increase the prevalence of their family's genes in future generations by providing resources e. Significant linkage was also detected in the pericentromeric region of chromosome 8, overlapping with one of the regions detected in the Hamer lab's previous genomewide study. Asexual Bisexual Heterosexual Homosexual. Scholars have also pointed out that Darwin himself described kin selection in The Origin of Speciesso under a Darwinian model of evolution, not only individuals, but family groups bloodlines can compete for selection. They also found that "unusually high" proportions of homosexual males and homosexual females were Rh negative in comparison to heterosexuals. If there are male-loving and female-loving alleles of tens or hundreds of genes battling it out in the population, everyone will inherit a mixture of different variants. It had been presumed that the overactive TSHR hormone lowered body weight in gay people.
Horm Res Submitted manuscript. Six of these men had died of AIDS-related illnesses. Views Read Edit View history. Sexual practices that significantly reduce the frequency of heterosexual intercourse also significantly decrease the chances of successful reproduction, and for this reason, they would appear to be maladaptive in an evolutionary context following a simple Darwinian model competition amongst individuals of natural selection—on the assumption that homosexuality would reduce this frequency. And all of the studies are based on memory and self-report that may not be entirely accurate.