Fig. 3

Examples of distribution of age at menarche ((a) and (b)), and distribution of duration of post-partum amenorrhea (c). (a) During a stable period, years 1300–1400, mean age 17.0 years, N = 1129, (b) during linear increase of the environment resources term, year 600–700, mean age 12.0 years, N = 410, and (c) during a stable period, years 1300–1400, mean duration 19.1 months, N = 3770.