Puberty is the process of physical changes through which a child's body matures into an adult body capable of sexual reproduction.On average, females begin puberty at age 10 1/2  and complete puberty at ages 15-17; males begin at ages 11 1/2 -12 and complete puberty at ages 16-17.[1][2][3] The major landmark of puberty for females is menarche, the onset of menstruation, which occurs on average around age 12 1/2 .[2] For males, first ejaculation, spermarche, occurs on average at age 13.[4] In the 21st century, the average age at which children, especially females, reach specific markers of puberty is lower compared to the 19th century, when it was 15 for females and 17 for males (with age at first periods for females and voice-breaks for males being used as examples).[5] This can be due to any number of factors, including improved nutrition resulting in rapid body growth, increased weight and fat deposition,[6] or exposure to endocrine disruptors such as xenoestrogens, which can at times be due to food consumption or other environmental factors.[7][8] However, more modern archeological research suggests that the rate of puberty as it occurs now is comparable to other time periods.Before puberty, the external sex organs, known as primary sexual characteristics, are sex characteristics that distinguish males and females.