Why do humans have menopause? Do animals have menopause?

We have observed a strange phenomenon: most animals do not have menopause. Among primates, the closest biological relatives to humans are chimpanzees, and the genetic similarity between humans and chimpanzees is as high as 98.5%. Female chimpanzees do not have menopause, and they can give birth until they die, but their fertility will decline. This is also the common fertility pattern of most mammals on Earth, that is, the childbearing age is consistent with the life span. Human women enter menopause at around 50 years old, which means that they will lose their fertility forever. The average human life expectancy is now over 70 years old, which means that women cannot give birth in the last third of their lives. So, what is the significance of human menopause?

Menopause helps humans survive and reproduce

In fact, the reproductive period of human females is not short, but because humans have a long life span, they can still survive for a long time after the reproductive period, while other animals will die soon after losing their reproductive period. In comparison, people have the illusion that "the reproductive period of human females is shorter." One of the important reasons why human females live long is that women who have lost their reproductive ability can help their daughters who are in their reproductive period to feed their offspring, thereby increasing the survival rate of their offspring. Therefore, genes with longer life are selected and inherited. This is the famous "grandmother hypothesis."

The "grandmother hypothesis" holds that in the process of continuous evolution, adult humans live longer than adult apes because grandmothers help feed their grandchildren to promote genetic optimization. In the 1980s, two anthropologists lived with the Hadza people in Tanzania. They observed that old women would collect food every day to feed their grandchildren. Because old women take on the responsibility of raising grandchildren, young women can reproduce the next baby faster. If a family lacks old women, then young women will take on the entire burden of raising children, which will not only lead to a longer next breeding period, but also a lower survival rate of offspring. In nature, genes that help organisms reproduce better will be selected by natural selection. Scientists made a mathematical model prediction for the "grandmother hypothesis", using chimpanzees as a comparison item in the model. All other conditions remain unchanged, and only a little change in grandmother feeding is needed. The results show that chimpanzees will have a lifespan similar to that of humans in 50,000 years.

No species on Earth has ever had difficulty in giving birth, because once a difficult birth occurs, it means that the species will become extinct. However, after humans achieved upright walking, they actually had difficulty in giving birth. The probability of a woman having a difficult birth during the birth of her first child is very high. If there is no one to assist in the birth, she cannot give birth alone. Because humans have difficulty in giving birth, the cost of raising offspring will increase, and middle-aged women (around 50 years old) are required to participate in the work of raising offspring. If women can give birth until they are old, in primitive and agricultural societies without contraceptive technology, grandmothers will raise their own children and have no energy to help their daughters raise their children. Then the quality of human offspring will decline because they will not be carefully raised, which will be detrimental to human evolution.

Why do very few animals also have menopause?

In addition to humans, only a few species of whales on Earth experience menopause, such as killer whales and pilot whales. The average lifespan of female killer whales is 50 to 60 years old, but female killer whales generally stop ovulating and stop giving birth in their 30s and 40s. At this time, female killer whales are still strong and have no signs of aging. This shows that menopause is not unique to humans, it is a product of natural evolution. You may ask, since menopause is a product of natural evolution, then why did primates, which are most closely related to humans, not evolve menopause, while whales, which are very distantly related to humans, evolved menopause?

The proportional relationship between an animal's brain and body is called the "encephalization index." Generally speaking, the higher the encephalization index of an animal, the higher its intelligence. The animal with the highest encephalization index on Earth is human, followed by dolphins, then killer whales, and chimpanzees are ranked fourth. Although dolphins and killer whales have not evolved into intelligent life, their degree of socialization is very high. Scientific research has found that killer whales seem to maintain a matriarchal clan structure, and the grandmother whale plays a key role in the group. After stopping ovulation, it will become the leader of the family. Female killer whales automatically stop giving birth, in fact, to help younger female killer whales raise their offspring.

Why most animals don't have menopause

Why do most animals, except humans and a few whales, not have menopause? The reason why most animals do not have menopause is that other animals will die of aging and inability to hunt soon after losing their fertility, which means that they have died before menopause.

There are many reproductive strategies, and the "grandmother hypothesis" is just one of them; and the survival of the grandmother also consumes energy. For many animals, sacrificing old and reproductively incapable individuals can save energy and increase the survival rate of offspring. This is also the reason why most animals do not have menopause.