The course of a menstrual cycle is pretty straightforward. Every month, under the effect of hormones, a female body will release a mature egg. The lining of the uterus, called endometrium, thickens, divides into layers, and grows a vast network of blood vessels to receive a fertilized egg.
If the egg gets fertilized, a woman becomes pregnant. If the egg isn’t fertilized, it dies and gets expelled from the body, along with that thick endometrial tissue and some blood. This sort of vaginal bleeding occurs as part of a female’s monthly cycle.
During that, sneezing, coughing, or laughing while on period seems like living on the edge, and having a boyfriend just breathing next to you seems like a declaration of war.
Menstruation has been well-documented in humans, but what about monkeys? Do monkeys get their monthly periods?
Yes, monkeys have periods. Apart from humans, most Old World monkeys and apes, as well as several New World monkeys experience periods. Monkeys will exhibit menstrual cycles that resemble those of human beings.
Japanese monkeys, for example, will usually have their first menstrual cycles (menarche) with ovulation around the age of three – if they become pregnant in this period, they give their first births in the next birth season.
Do Monkeys Have Menstrual Cramps?
There have been several reported cases suggesting that monkeys experience menstrual cramps during their periods.
One study on rhesus monkeys showed that increased estradiol levels (a form of the hormone estrogen) were associated with higher prostaglandin levels (chemicals produced by the uterus), which are known to cause menstrual cramps.
Another study on rhesus monkeys noticed that one 13-year old female was intermittently anorexic and dysmenorrheic. The monkey could be seen sitting hunched on the floor of the cage holding the abdomen and had irregular menstruation.
Therefore, it is very much possible that monkeys experience the same sort of cramps and menstrual discomfort as humans do.
Do Monkeys Have PMS And How Do They Deal With Periods?
Yes, some species of monkeys can experience PMS, just like humans do. Monkeys dealing with premenstrual syndrome (PMS) will show physical and behavioral changes, like skin color changes, increased irritation and aggression, and mood swings.
During the luteal phase of the cycle, just before getting their period, monkeys will have food cravings, and eat more. Something not very unfamiliar with women.
In one species of Old World monkeys native to Africa, the vervet monkey, scientists noticed that females on their periods tend to significantly alter their behavior.
During the late luteal phase, when the progesterone level decreases, vervet monkeys will become more aggressive and show combative behavior, especially the leading female.
Some members of the group on periods would move away from a threat or an approaching animal, while other monkeys would bite, chase, slap, or full-body attack.
The dominant female monkey becomes significantly more aggressive and less sociable than when she is in her follicular phase (the stage of the menstrual cycle when the body is preparing to release an egg). Scientists seem to think that such behavior by the alpha female elicits similar behavior in subordinate females.
In this regard, vervet monkeys show the same amount of irritability that can be seen in women with PMS.
During their premenstrual phase, yellow baboons will avoid social contact, while rhesus monkeys become more aggressive as their period approaches. In one study of rhesus monkeys, scientists noted that they would bite each other a lot more in the 7 days before their menses.
How Often Do Monkeys Have Periods?
Monkeys will have periods throughout the year, usually lasting around 28 days. During their reproductive season (from October to February), monkeys will have a short and regular period; during the non-reproductive season (March through September) it becomes irregular or sometimes completely absent.
Old World monkeys have menstrual cycles that last from 24 to 35 days, similar to human females. In New World monkeys, the cycle lasts from 16 to 30 days, while in squirrel monkeys the cycle length is just 7-12 days.
The shortest menstrual cycle recorded in rhesus monkeys (Old World monkeys) was 16 days, while the longest was over 60 days.
Just like humans, monkeys also experience vaginal bleeding. Uterine bleeding in monkeys lasts between 1 and 7 days, depending on the species.
In rhesus monkeys, ovulation will occur between days 15 and 20 of their menstrual cycle.
Do Monkeys Go Through Menopause?
Just like humans, monkeys experience menopause. At a certain age, monkeys lose their menstrual cycle, stop ovulating and bleeding, and will no longer be able to reproduce.
Humans will stop menstruating around the age of 50. If the maximum age of humans is 122 years, this means that females will have 60% of their life in a postreproductive state (age at which they can no longer expect to produce offspring).
Macaque monkeys will stop menstruating and enter menopause around the age of 25. In captivity, these monkeys can live up to 40 years – about 40% of the maximum life span of these monkeys is postreproductive.
Baboons, the world’s largest monkeys, will stop menstruating and get into menopause around the age of 26.
A study published in the Biology of Reproduction Journal discovered that some apes, like the gorilla, will get into menopause around the age of 40, while chimpanzees and bonobos enter menopause between the ages of 35 and 50.
Final Thoughts – Do Monkeys Have Periods?
Yes, monkeys and some other primates will have menstrual cycles every 25-30 days and even bleed, just like humans. There will be different physical changes (female monkeys in period will have their skin become redder), and some behavioral ones (monkeys will become more irritable and more aggressive); something that is noticeable in humans.
This is all followed by various hormonal changes (like the changes in estrogen, progesterone, gonadotropin-releasing hormone, follicle-stimulating hormone, and luteinizing hormone levels).
Another similarity is that at the end of their reproductive powers, monkeys will enter menopause.
Either way, this might seem like a small comfort for women, to know that their pain is shared with other female primates.