Menstrual synchrony
Strassmann argued menstrual synchrony defined as menstruation overlap should be quite common. For example, the expected difference by chance between two women with 28-day cycles—which is approximately the average length of menstrual cycles of women at the age —is 7 days. Considering that the mean duration of menses is 5 days and the range is 2 to 7 days, the probability of menstruation overlap by chance should be high.
Common treeshrew
Both sexes of common treeshrews are sexually mature at the age of about three months. In captivity, females give birth for the first time at the age of about 4.5 mo, usually in February. A postpartum oestrus results in more births in April. Their oestrus cycle is eight to 39 days, and the gestation period lasts 40 to 52 days, after which a litter of one to three individuals is born. The newborn offspring weigh about 10 to 12 grams. Females suckle their young every other day, and neglect their young as long as possible. They would not even be able to identify their own young if they did not mark them with the scent produced from glands in their sternum and abdomen. Juveniles leave the nest between 25 and 35 days of age. Longevity of a captive common treeshrew has been recorded as 12 yr and 5 mo.