Menopause and its evolutionary roots

Menopause is a stage of female life that marks the end of reproductive capacity, generally between 45 and 55 years of age. Although it may seem contradictory from a biological perspective for an organism to cease its reproductive capacity before the end of its life, in the case of humans and some other mammals this stage has served a fundamental adaptive purpose.

Menopause is defined as the permanent cessation of menstrual cycles, which occurs when the ovaries stop producing sex hormones, primarily estrogen and progesterone. This natural process has important implications for female biology, as it marks the end of fertility. Although menopause is common in humans, there are very few cases in nature where an organism ceases to be fertile long before death.

In reality, only a few mammals besides humans experience menopause, including some species of whales and dolphins. This phenomenon is exceptional in the animal kingdom, and its existence has intrigued scientists from different disciplines for decades.

Main Evolutionary Theories of Menopause

To understand why menopause has endured as part of human development, several evolutionary theories have been formulated. These hypotheses suggest that menopause may have conferred specific advantages for the survival of women and, ultimately, for the survival of the species. The main theories are the following:

1. The Grandmother Hypothesis

The grandmother’s hypothesis is one of the most accepted theories and proposes that menopause evolved to allow older women to contribute to the well-being of their descendants and grandchildren. According to this hypothesis, postmenopausal women who no longer have to devote time and energy to their own children can devote those resources to caring for their grandchildren, thus increasing the chances of survival of the next generation.

Postmenopausal women can provide support and help in childcare, food gathering, and knowledge transmission, strengthening family and community unity. This theory finds support in anthropological studies that show how grandmothers have played key roles in the survival of families in hunter-gatherer societies.

2. Theory of Reproductive Efficiency

Another theory suggests that menopause may have evolved as a mechanism to reduce the risks associated with pregnancy and childbirth at older ages. In ancient societies, the risk of complications during pregnancy increased significantly with the mother’s age. By ending fertility in mid-life, menopause would have protected women from the dangers of late pregnancy and the potentially lethal consequences that come with it.

Reproductive efficiency theory suggests that the female body has a time limit in which it is safe to reproduce and that, by eliminating the possibility of pregnancy in later life, menopause contributed to increased female longevity. This aspect would also have allowed older women to play essential roles in their groups without the wear and tear of risks associated with childbirth.

3. Theory of Natural Selection for Longevity

The adaptive longevity theory maintains that menopause is a consequence of natural selection that favored long-lived individuals. According to this hypothesis, living beyond reproductive age would not have a disadvantage in itself, but on the contrary, genes that favor longevity would have been advantageous for the human species, since these older individuals not only contribute to the care of their grandchildren, but also to the transmission of knowledge and skills that increase the chances of survival of the community.

By living longer and going through menopause, women would have the opportunity to significantly influence the structure and social cohesion of their groups. Knowledge about medicinal plants, hunting or cultivation techniques, as well as personal life experiences, are part of an evolutionary legacy that strengthens the survival of the human species.

Menopause and the Human Brain: A Cognitive Advantage

Recent research has suggested that menopause may also be related to cognitive development in humans. Women’s ability to remain mentally active and emotionally involved in their communities could have been a selective advantage, since the transmission of cultural knowledge is vital in human evolution. Thus, menopause would not only have allowed women to actively participate in their communities, but would have encouraged the development of advanced cognitive and social skills that have shaped the modern human brain.

Why is Menopause Rare in Other Animals?

The evolution of menopause is closely linked to the complex social structures and interdependence of humans, which explains its rarity in other animals. In most species, reproduction and survival of offspring depends primarily on individuals of reproductive age, with older adults usually having little or no role in the group.

Instead, in humans and some species of whales, the care and support of older individuals significantly improves the survival of offspring, providing an evolutionary reason for menopause and longevity to persist.