All female placental mammals have a uterine lining that builds up when the animal is fertile, but is dismantled (menstruated) when the animal is infertile.
Some anthropologists have questioned the energy cost of rebuilding the endometrium every fertility cycle. However, anthropologist Beverly Strassmann has proposed that the energy savings of not having to ''continuously'' maintain the uterine lining more than offsets energy cost of having to rebuild the lining in the next fertility cycle, even in species such as humans where much of the lining is lost through bleeding (overt menstruation) rather than reabsorbed (covert menstruation). However, even in humans, much of it is re-absorbed.
Many have questioned the evolution of overt menstruation in humans and related species, speculating on what advantage there could be to losing blood associated with dismantling the endometrium rather than absorbing it, as most mammals do.
Beginning in 1971, some research suggested that menstrual cycles of co-habiting human females became synchronized. A few anthropologists hypothesized that in hunter-gatherer societies, males would go on hunting journeys whilst the females of the tribe were menstruating, speculating that the females would not have been as receptive to sexual relations while menstruating. However, there is currently significant dispute as to whether menstrual synchrony exists.
Humans do, in fact, reabsorb about two-thirds of the endometrium each cycle. Strassmann asserts that overt menstruation occurs not because it is beneficial in itself. Rather, the fetal development of these species requires a more developed endometrium, one which is too thick to completely reabsorb. Strassman correlates species that have overt menstruation to those that have a large uterus relative to the adult female body size.
Many religions have menstruation-related traditions. These may be bans on certain actions during menstruation (such as intercourse in orthodox Judaism, Hinduism and Islam), or rituals to be performed at the end of each menses (such as the ''mikvah'' in Judaism and the ''ghusl'' in Islam). Some traditional societies sequester females in residences, "menstrual huts", that are reserved for that exclusive purpose until the end of their menstrual period.
Since the late 1960s, some women have chosen to control the frequency of menstruation with long-acting hormonal birth control. This allows women to plan months in advance when she will menstruate as combined hormone pills are taken in 28 day cycles, 21 hormonal pills with either a 7 day break from pills, or 7 placebo pills during which the woman menstruates. Injections such as depo-provera became available in the 1960s, progestogen implants such as Norplant in the 1980s and extended cycle combined oral contraceptive pills in the early 2000s.
This article is licensed under the Creative Commons Attribution-ShareAlike License.
It uses material from the Wikipedia article on
All material adapted used from Wikipedia is available under the terms of the
Creative Commons Attribution-ShareAlike License.
Wikipedia® itself is a registered trademark of the Wikimedia Foundation, Inc.