What animals, along with humans, experience menopause and menstruation?

Research suggests that female humans are not the only species that menopause and menstruation arises in. All iteroparous organisms menstruate, however only a handful overtly menstruate (blood flows from the uterus through the vagina) while others menstruate covertly (by reabsorbing the uterine lining into the body). Overt menstruating females are generally sexually active throughout their cycle, whilst covert menstruating females are only ‘in heat’ mid-cycle (Wallen & Zehr, 2004).

Figure 1. Chimpanzee (Pan troglodytes). C.Bromhall (2015)

Overt menstruation occurs in humans, most primates (including chimpanzees, orang-utans, gorillas and rhesus monkeys etc.), some species of fruit bats, and elephant shrews. Menstrual bleeding in non-human primates is minimal. However, orang-utans and opossums have an average cycle length of 28 days which is closest to that of humans, while chimpanzees have an average cycle length of 35 days (Lacreuse et al., 208). Covert menstruation occurs in all placental mammals (including cats, dogs, rats, horses, pigs and elephants etc.)

 

Figure 2. Placental Mammals and Marsupial Mammals. Anon. (2015).

Most other egg-laying mammals (including some reptiles, some amphibians, some fish and most birds, excluding macaques; Brenner et al. 2012) do not menstruate. It is interesting to note that humans actually reabsorb about two-thirds of the uterus lining in each cycle (covert menstruation). Therefore only one-third of the human uterus lining is overtly menstruated (Lacreuse et al., 208), while the other two-thirds is covertly menstruated. 

It is found that a vast majority of animals do actually menstruate, whether it is overtly or covertly mensuration, only a few species actually experience menopause. The species that do experience menopause (apart from humans) include the killer whales and (short-finned) pilot whales (Johnstone et al. 2010; Peccei, 2001; Flinn, 2013).

So why does menopause only occur in these three species?

References:

Anonymous. (2015). Convergent Evolution Marsupials and Placental Mammals. http://becuo.com/convergent-evolution-marsupials-and-placental-mammals; Retrieved 27/03/2015.

Bromhall, C. (2015). Chimpanzee (Pan troglodytes). http://www.arkive.org/chimpanzee/pan-troglodytes/image-G4540.html; Retrieved 27/03/2015.

Brenner, R.M., & Slayden, O.D. (2012). Molecular and functional aspects of menstruation in the macaque. 10.1007/s11154-012-9225-5.

Flinn, M.V. (2013). Are humans the only species that go through menopause? http://www.researchgate.net/post/Are_humans_the_only_species_that_go_through_menopause; Retrieved 27/03/2015.

Johnstone, R.A., & Cant, M.A. (2010). The evolution of menopause in cetaceans and humans: the role of demography, 277(1701):3765-3771. Doi: 10.1098/rspb.2010.0988.

Lacreuse, A., Chennareddi, L., Gould, K.G., Hawkes, K., Wijayawardana, S.R., Chen, J., Easley, K.A., Herndon, J.G. (2008). Menstrual Cycles Continue into Advance Old Age in the common Chimpanzee (Pan troglodytes). 79(3): 407- 412. Doi:10.1095/biolreprod.108.068494.

Peccei, J.S. (2001). Menopause: Adaptation or Epiphenomenon. Evolutionary Anthropology, 10:43-57.

Wallen, K. & Zehr, J.L. (2004). Hormones and History: The evolution and Development of Primate Female Sexuality. 41(1): 101-112. Doi:10.1080/00224490409552218.

How could such a maladaptive trait evolve?

An evolutionary explanation for menopause suggests a “grandmother” hypothesis which proposes that post-reproductive survival is favoured by kin selection as relatives are helped by older females with reproduction (Johnstone & Cant. 2010). Another evolutionary explanation suggests that menopause is a hominine adaptation, and the climacterium (a developmental phase accompanying menopause (McKinlay. 1996)) evolved due to intense reproductive investment early in life, or to ‘prevent’ reproduction late in life as there are such large costs following with only small benefits (Peccei. 2001).

Jacobson, M. The Sandwich Generation: Raising Kids, Caring for Parents (2015).

Reproductive investment is costly in humans as offspring require a long period of dependence as they are born helpless. This high cost becomes disadvantageous as there is a large number of dependent offspring due to such short inter-birth intervals, and all of which are nurtured simultaneously in humans. However, there are only small benefits in late reproduction as there is an elevated risk of the fetus having a defect, being born small or being miscarried (Peccei. 2001).

Late reproduction may be costly, but, for a young mother to die during or shortly after childbirth jeopardizes the life of not only the current child but also for the children which are still heavily dependent on their mother for not only protection but for nourishment also (Johnstons & Cant. 2010).

                             

Thus concluding that menopause may have evolved due to the costs of late reproduction out-weighing the benefits that accompany it, as well evolving genes selected to cease reproduction early compared to the genes that would allow for risky reproduction late in life (Lahdenpera et al. 2004 & Peccei. 2001).

So now it is known how this maladaptive trait has evolved, my next question is; what animals, along with humans, experience menopause and menstruation?

References:

Jacobson, M. (2015). The Sandwich Generation: Raising Kids, Caring for Parents. https://www.parentmap.com/article/the-sandwich-generation-raising-kids-caring-for-parents; retrieved 20/03/2015.

Johnstone, R.A., & Cant, M.A. (2010). The evolution of menopause in cetaceans and humans: the role of demography, 277(1701):3765-3771. Doi: 10.1098/rspb.2010.0988.

Lahdenpera, M., Lummaa, V. & Russel, A.F. (2004). Menopause: why does fertility end before life? 7:327-332.

McKinlay, S.M. (1996). The normal menopause transition: an overview, 23(2): 137-145. Doi: 10.1013/0378-5122(95)00985-X.

Peccei, J.S. (2001). Menopause: Adaptation or Epiphenomenon. Evolutionary Anthropology, 10:43-57. 

Menopause - What is it?

Menopause can be defined on so many levels depending on one’s individual experience. Some say it represents negative changes in women's lives while others propose it to represent either neutral experiences or positive change within individual woman as (Dillaway, 2005) states. However, menopause is a natural biological process that is defined as the permanent cessation of menstruation (Sherman, 1998) which affects all women around the age of 50 years old.

The depletion of ovarian follicles characterises menopause in humans (Derry, 2006). The ovarian follicles are located within the ovary as immature eggs. These eggs are surrounded by an envelope of cells that produce reproductive hormones needed for the menstrual cycle to orchestrate.

During puberty, the brain’s pituitary glands stimulate the ovaries to begin ovulation (releasing eggs each month). In preparation for the plantation of a fertilised egg, the stimulation of the pituitary glands then promotes the ovaries to release oestrogen and progesterone, thus allowing the lining of the uterus (endometrium) to thicken. A period occurs as the endometrium is shed if an egg does not become fertilised. This is known as the menstrual cycle

The number of follicles in the ovaries and level of hormones decrease as a woman ages. Menopause occurs when the period stops permanently due to the failure of the ovaries to produce enough hormones to stimulate monthly growth of the endometrium (. 2015).

Securing your genetic legacy by reproducing as many offspring as possible is seen as “winning” in the game of evolution. So it seems to be counter-intuitive that women have evolved in such a way that their fertility diminishes decades before they pass.

So my question is, how could such a maladaptive trait evolve?

References:

Dalliway, H.E. (2005). (Un)Changing Menopausal Bodies: How Women Think and Act in the Face of Reproductive Transition and Gendered Beauty Ideas. Sex Roles, 53(1-2), 1-17. Retrieved from http://link.springer.com/article/10.1007/s11199-005-4269-6.

Derry, P.S. (2006). A Lifespan biological theory of menopause. Sex Rolews. 54, 393-399.

Geary, D.C. & Flinn, M.V. 2001. Evolution of human parental behaviour and the human family. Parenting: Science and Practices, 1 (1&2), 5-61.

Sherman. P.W. (1998).l Animal Behavior; The Evolution of menopause. Nature, 392, 759-761. doi:10:1038/3385.

Wayman, E. (2013). Killer whales, grandmas and what men want: Evolutionary biologists consider menopause. Retrieved from https://www.sciencenews.org/article/killer-whales-grandmas-and-what-men-want-evolutionary-biologists-consider-menopause.

. 2015. [ONLINE] Available at: https://www.asrm.org/uploadedFiles/ASRM_Content/Resources/Patient_Resources/Fact_Sheets_and_Info_Booklets/agefertility.pdf. [Accessed 13 March 2015].