Sex differences in human physiology

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Sex differences in human physiology are distinctions of physiological characteristics associated with either male or female humans. These differences are caused by the effects of the different sex chromosome complement in males and females, and differential exposure to gonadal sex hormones during development. Sexual dimorphism is a term for the phenotypic difference between males and females of the same species.

The process of meiosis and fertilization (with rare exceptions) results in a zygote with either two X chromosomes (an XX female) or one X and one Y chromosome (an XY male) which then develops the typical female or male phenotype. Physiological sex differences include discrete features such as the respective male and female reproductive systems, as well as average differences between males and females including size and strength, bodily proportions, hair distribution, breast differentiation, voice pitch, and brain size and structure.

Other than external genitals, there are few physical differences between male and female children before puberty. Small differences in height and start of physical maturity are seen. The gradual growth in sex difference throughout a person's life is a product of various hormones. Testosterone is the major active hormone in male development while estrogen is the dominant female hormone. These hormones are not, however, limited to each sex. Both males and females have both testosterone and estrogen.^[1]