Human breasts are different from all the other breasts on the planet.
Humans are the only mammals to have breasts that develop in puberty and then remain permanently enlarged, says Florence Williams, the author of Breasts: A Natural and Unnatural History.
Williams was fascinated to learn that our breasts are the last organ in our bodies to develop.
Unlike, say, the brain or liver, whose architecture is set at birth, breasts don't really come into their own until well after birth.
"Even if a woman never gets pregnant, her breasts pack and unpack a little bit each month, just in case."
Over the course of a menstrual cycle, breast volume varies by 13.6 percent, owing to water retention and cell growth.
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