A fetus usually develops into a male if it is exposed to a significant amount of testosterone (typically because the fetus has a Y chromosome from the father).Otherwise, the fetus usually develops into a female, typically when the fetus has an X chromosome from the father, but also when the father contributed neither an X nor Y chromosome.In some cases, even if a child had XX chromosomes, if they were born with a penis, they were raised as a male.There are also transgender and transsexual women, who were assigned as male at birth, but identify as women; there are varying social, legal, and individual definitions with regard to these issues (see trans woman).The breast evolved from the sweat gland to produce milk, a nutritious secretion that is the most distinctive characteristic of mammals, along with live birth.
An imbalance of maternal hormonal levels and some chemicals (or drugs) may alter the secondary sexual characteristics of fetuses. The term girl is the usual term for a female child or adolescent.The term woman, however, may also be used as the general term to identify a female human, regardless of age, as in phrases such as "women's rights".For instance, intersex individuals, who have mixed physical and/or genetic features, may use other criteria in making a clear determination.At birth, babies may be assigned a gender based on their genitalia.The medial labial consonants f and m in wīfmann coalesced into the modern form "woman", while the initial element wīf, which meant "female", underwent semantic narrowing to the sense of a married woman ("wife").It is a popular misconception that the term "woman" is etymologically connected to "womb".(For other ways in which men commonly differ physically from women, see man.) During early fetal development, embryos of both sexes appear gender-neutral.As in cases without two sexes, such as species that reproduce asexually, the gender-neutral appearance is closer to female than to male.In Old English, wīfmann meant "female human", whereas wēr meant "male human".Mann or monn had a gender-neutral meaning of "human", corresponding to Modern English "person" or "someone"; however, subsequent to the Norman Conquest, man began to be used more in reference to "male human", and by the late 13th century had begun to eclipse usage of the older term wēr.