An intersexual or intersex person (or animal of any unisexual species) is one who is born with genitalia and/or secondary sex characteristics determined as neither exclusively male nor female, or which combine features of the male and female sexes. more...
(The terms hermaphrodite and pseudohermaphrodite, which have been used in the past, are now considered pejorative and inaccurate and are no longer used to refer to an intersexual person.) Sometimes the phrase "ambiguous genitalia" is used.
According to the highest estimates (Fausto-Sterling et. al., 2000) perhaps 1 percent of live births exhibit some degree of sexual ambiguity , and that between 0.1% and 0.2% of live births are ambiguous enough to become the subject of specialist medical attention, including surgery to disguise their sexual ambiguity. Other sources (Leonard Sax, 2002) estimate the incidence of true intersexual conditions as far lower, at approximately 0.018%.
In typical fetal development, the presence of the SRY gene causes the fetal gonads to become testes; the absence of it allows the gonads to continue to develop into ovaries. Thereafter, the development of the internal reproductive organs and the external genitalia is determined by hormones produced by certain fetal gonads (ovaries or testes) and the cells' response to them. The initial appearance of the fetal genitalia (a few weeks after conception) is basically feminine: a pair of "urogenital folds" with a small protuberance in the middle, and the urethra behind the protuberance. If the fetus has testes, and if the testes produce testosterone, and if the cells of the genitals respond to the testosterone, the outer urogenital folds swell and fuse in the midline to produce the scrotum; the protuberance grows larger and straighter to form the penis; the inner urogenital swellings swell, wrap around the penis, and fuse in the midline to form the penile urethra.
Because there is variation in all of these processes, a child can be born with a sexual anatomy that is typically female, or feminine in appearance with a larger than average clitoris; or typically male, masculine in appearance with a smaller than average penis that is open along the underside. The appearance may be quite ambiguous, describable as female genitals with a very large clitoris and partially fused labia, or as male genitals with a very small penis, completely open along the midline ("hypospadic"), and empty scrotum.
There are dozens of named medical conditions that may lead to intersex anatomy. Fertility is variable. The distinctions "male pseudohermaphrodite", "female pseudohermaphrodite" and especially "true hermaphrodite" are vestiges of 19th century thinking that placed "true sex" in the histology (microscopic appearance) of the gonads.
The common habit in the 21st century of elevating the role of the sex chromosomes above all other factors when determining gender may be analogous to the older habit of finding "true" sex in the gonads. Though high school biology teaches that men have XY and women XX chromosomes, in fact there are quite a few other possible combinations such as Turner_syndrome XO, Triple-X syndrome XXX, Klinefelter's Syndrome XXY, XYY, XO/XY, XX male, Swyer syndrome XY female, and there are many individuals who do not follow the typical patterns (such as cases with four or even more sex chromosomes).
Read more at Wikipedia.org