Of all the mammals on Earth, only humans do not have estrus.
The estrous cycle, also known as the estrous cycle, is a recurrent physiological change possessed by female placental mammals, induced by the body's sex hormones.
The length of time between the previous ovulation and the next ovulation is called a cycle. The concentration of various hormones in the animal, as well as the fertility of the animal, all vary with the estrous cycle. Various animals have different estrous cycle lengths.
The estrous cycle begins in sexually mature adolescent females and stops temporarily during estrus or pregnancy until the next cycle begins. This cycle will continue until death.
There is no estrus cycle in humans, humans only exist in the menstrual cycle, the professional term is concealed ovulation (hidden ovulation), there is a clear physiological difference between the two, animals with estrous cycles will reabsorb the endometrium when they are not pregnant; Humans remove the endometrium from the body during menstruation. Another is that animals with estrous cycles will have a fixed period of sexual activity, during which they will ovulate spontaneously or stimulantly. And the menstrual cycle will cause human women to form bulging breasts and ** membranes.
From the perspective of other animals, it is indeed a very funny thing for humans to hide their ovulation period. We can now see that many women trying to conceive need to use a thermometer and break their fingers to barely calculate the ovulation and safety periods. Of course, these are "Schrödinger's ovulation calculation method" - until the moment you get pregnant, you don't know if you have calculated it correctly.
Why doesn't there be an estrus period in humans? This is something that scientists are very confused about.
Previously, the most dominant view was the "paternity investment hypothesis", in which all 4,000 species of mammals and more than 200 species of primates were fertilized and conceived in females. The vast majority of these small animals, just born or even before they were born, are like "losing their father".
Males only provide sperm and do nothing else to get a cub that carries their own genes. Because for creatures in nature, reproduction is the core meaning of their own survival.
But humans are different, as bipeds, they are the only creatures that need to be assisted in childbirth, and they have a narrow birth canal and an unusually large head. To reduce the risk of childbirth, humans have evolved shorter gestation periods that allow the baby's head to pass safely through the birth canal, but this has also led to the consequence that the baby is born before the brain is fully developed.
Curiously, the amount of time a baby spends developing in the womb is reduced, and the minimum lactation period required after birth is not extended, but is also drastically reduced. The age of weaning for babies can be as short as:
Children who are three or four months old, but weaned early, still need to be fed.
Pregnancy, breastfeeding, and caring for freshly weaned women all require a lot of energy and time. She had to consume more food first and then feed her children, and her foraging ability was declining all the time. Mom needs to find someone who, like her, has a genetic investment in her children and can raise their offspring together – and that person, of course, is Dad.
The paternal parentage investment hypothesis suggests that the mother's hidden ovulation period can prompt the father to assume the responsibility of reproducing offspring. Once the females hide their ovulation and no longer signal the time of ovulation, the males will not be able to detect the exact time of their conception. This has led to a change in the mating strategy of men: instead of marrying multiple women, hoping that some of them will be able to have children at least during that period, it is better to choose a fixed partner who has a higher rate of successful pregnancy.
And females also have the right to choose a mate, if they mate with multiple males during ovulation, then there will be a problem of paternal indeterminacy. Therefore, for the sake of the stability of their genetic inheritance, males will be more willing to stay by the female's side, and gradually assume the responsibility of raising them, and the paternal parents will invest in joining. This not only reduces the burden on the mother, but also greatly improves the survival rate of the baby.
This has also promoted the development and continuation of human civilization, and the complexity of human life has increased, and young people need to learn a lot of knowledge: how to cooperate with others when hunting, and what are the skills? How to make a production tool? What is the surrounding terrain like? All of this needs to be taught by the father to the adolescent, so the father becomes the child's teacher, the knowledge and experience are continued, the neocortex, the higher cognitive area of the brain, the neuronal connectivity will also be enhanced, and the number will increase, and this is how people develop step by step. In modern society, fathers still fulfill this teaching role, teaching their children various social skills.
A recent study published in Nature Human Behavior has questioned this long-standing theory. Based on computer models, a team of evolutionary scientists has shown that the actual advantage of hiding ovulation is that it allows females to hide their fertility status from other females.
Scientists used computers to build models that divided men into "responsible" and "irresponsible", and women into "ovulation with obvious characteristics" and "ovulation with inconspicuous characteristics", and set it on the map: female groups will crowd out the same sex in ovulation (because they show fertility potential, resources will be skewed).
The model supports the female competition hypothesis. Women who hide their ovulation give birth to more children, avoid being victimized by the same people, and successfully establish a stable relationship with men.
Although there are differences, the core of both views is that the choice made by females for the survival of their babies, and the hidden ovulation of females, which scientists believe was the key to the transition from polygamy to monogamy in early humans. From this point of view, women are great, and the choices they make play a crucial role in the formation of the human structure.
Scientific rambling