In these cultures, the methods of childrearing and nurturing were similar. These babies were usually breastfed for 2 to 3 years. Later records show that Hebrews nursed for 3 years as the child was then old enough to enter the Temple. The Talmud, in 536 BC, stated that the baby should be nursed immediately and continue until 18 months to 2 years. The Qur'an says that children should breastfeed for at least 2 years.
Cultural norms reflect beliefs.
However, anthropologist Kathryn Dettwyler was interested in the nursing duration of humans from the standpoint of mammalian behavior. She wanted to find out how long a human would breastfeed according to our physical characteristics, not what would be dictated by tribal or cultural practices. She looked at research and found that there were several markers for the length of time that large mammals nursed their young. One is the quadrupling of the birth weight. Using this method, American babies born at around 7 pounds will quadruple their weight sometime between 2 and 3 years.