Much has been debated about equal rights for same-sex civil marriage, but little emphasis is given to scientific bases that support that homosexuality is structurally and physiologically natural in the human brain.HUNDREDS of scientific studies in scientific journals of high impact and high reliability are available in English, and support that homosexuality is not choice, it's a biological condition. There are studies done testing animals, and also in post-mortem humans (and some published studies are available on the links below) that prove that sexuality is a result of hormonal conditions even during fetal life, before birth, and that emerge at puberty. Look at the figures 4 and 6 of this scientific article in this PDF link (http://1drv.ms/1qjQmWC)This article shows very clearly what happens to pregnant females induced with testosterone during the fetal period in rats. The opposite is also true, high amounts of estradiol in the fetal period can feminize a male.Another article that supports this thesis is this mini review is http://1drv.ms/1qjUvKc, which is compiled of 76 other papers around the world, the most experienced guys in the area, and explains why, in both humans and animals, this hormonal system functions in the fetus.Notice in Figure 2 (Theoretical model illustrating how fluctuations around an average concentration of testosterone (T) during embryonic life could lead to a heterosexual or homosexual). Low concentrations of testosterone during fetal life of a boy, would take him to be bi, gay or even transsexual (as lower the testosterone produced by him during the fetal stage - yes, boys fetuses produce MUCH testosterone during the first couple of months of life). The same thing would happen with girls fetuses had a certain blood testosterone, either the mother or fetus, could lead to homosexuality in girls, or even transsexualism. An analogy could be this: Imagine as if the baby in the womb were a glass of milk, and you can put Chocolate (boy) or Strawberry (girl) ... or both. Remembering, the mother is always full of strawberry flavor. Hormones can change in the body. Testosterone can be converted to progesterone and even estrogen, depending of enzymes present in the body.GETTING DEEP IN THE SCIENCE: (bold for important conclusions)A study published in the journal Endocrinology (Endocrinology), says that sexual orientation is a sexually differentiated trait (more than 90% of men are attracted to women and vice versa). In animals and humans, many sexual characteristics are organized during the prenatal period by sex steroids, and we can say that the same mechanism also affects human sexual orientation. The clinical conditions associated with significant endocrine changes during embryonic life often result in an increased incidence of homosexuality. The prenatal endocrine environment has a significant influence on human sexual orientation, but a large fraction of the variance in this behavioral characteristic remains unexplained to date. The genetic differences that affect behavior, either directly or by altering the secretion of embryonic hormones may also be involved. (Copyright 2011 by The Endocrine Society doi: 10.1210 / en.2011-0277 Received March 10, 2011 Accepted May 31, 2011 Endocrinology, August 2011, 152 (8): 2937-2947 endo.endojournals.org 2937) Despite