In the etiological studies of mental illness, it has long been found that role confusion in the families of schizophrenic patients, especially weak or absent father role, too strong mother role or mother role alone, has a significant impact on the development of schizophrenia in their children. However, as an affective disorder physician with a focus on diagnosis and treatment of mood and anxiety disorders, I have also found in my own clinical and research work that characteristics such as weak or absent father roles or strong mother roles are similarly prominent in the families of patients with bipolar disorder and anxiety disorders. Such similarities made me wonder why father role absence has such serious consequences. Differences between fathers’ and mothers’ child-rearing behaviors and their biological basis I first approach the role of the father role from a biological and evolutionary basis. According to biological principles, any organism that reproduces sexually, whether it is a plant or an animal, requires the union of two reproductive cells of the opposite sex, in which the DNA carrying the genetic information of the two parties merges to form a new cell, which is the so-called “fertilized egg”. This fertilized egg, which carries half of the genetic information (DNA) of each parent, develops into a new individual under the right conditions and takes on the characteristics of a living organism. All sexually reproducing organisms in the biological world are reproduced in such a way that the lineage of organisms can flourish over a long period of history. It can be said that an individual organism emerges with the mission of reproducing its offspring so that the germline is guaranteed to live on. Through such reproduction, development, and growth of countless individuals of the same lineage, the rivers and oceans of the lineage are merged like a trickle of water. Therefore, organism self-preservation and germline preservation are the most important purposes for organisms to survive in nature, and, moreover, germline preservation is based on individual preservation. In the long evolutionary process of any kind of organism, a mechanism has been formed to protect the new life with the significance of germline continuation, that is, to ensure that the newborn individual strives to develop and mature into an individual capable of reproduction. Therefore, the parent generation of any animal in reproduction, giving birth to offspring will show the corresponding behavior of child care, so that childish individuals gradually grow and develop into mature individuals, in order to complete the instinctive activities of the significance of the “succession”. However, in the animal kingdom, animals of different genders have different patterns in ensuring the survival, development and growth of their offspring. In the animal kingdom, mature males and females serve different functions, especially in reproduction and nurturing of offspring, and this division of labor should be clearer than that of humans in modern society. Males are biologically endowed with behavioral traits such as aggression, predation, occupation, and pioneering, which are particularly evident when it comes to the resources needed for reproduction and the nurturing of offspring. The ultimate purpose of such characteristics and their behavior is also very clear, that is, to make the individual male have the most abundant resources possible, to attract female mates to mate with them, to reproduce their offspring, and to ensure that their offspring have sufficient living resources after birth, so that their offspring will have relatively sufficient material conditions for growth and development in their juvenile years. Such behavioral traits give males a tendency to be adventurous, exploratory, and aggressive, and inevitably a tendency to underestimate the risks they are currently facing. Of course, the ability to tenaciously overcome difficulties in the course of such behavior is also an essential condition. Assuming that males do not dare to initiate any aggressive and predatory actions with a certain degree of risk, such males will hardly have the resources to show off in order to attract mature females, and will not be able to obtain the opportunity to reproduce their offspring. This is similar to the desire of unmarried women in contemporary Chinese society for a man to have a car, a house, and money. Unlike males, females are biologically protective, conservative, and seek to maximize environmental security. These behaviors of females are also significant when it comes to parenting and nurturing activities, and the ultimate goal of these behaviors is quite clear: to reproduce and raise as many offspring as possible. For example, females choose the safest environment, the most conducive position for suckling and protection of their young while nursing them, etc., in order to ensure that their young are nurtured and safe for survival. Thus, females are predisposed to seek maximum security and, as a result, tend to overestimate the risks in their survival environment. If a female lacks these behavioral traits, her offspring are likely to have a greater chance of dying young, and she is much less likely to be the mother of a sufficiently large number of offspring. In general, the number of reproductive cells that males, especially mammalian males, can produce at maturity is virtually unlimited, and with a sufficient number of mates, males have the ability to reproduce far more offspring than one could ever imagine. For example, under normal circumstances, adult males ejaculate about 3-6 ml of semen per sexual activity, the number of spermatozoa in each ml of semen ranges from 20 million to 200 million, and the live spermatozoa should be more than 70% or a little lower, and theoretically, each live spermatozoa has the possibility of combining with a mature egg and developing into a fertilized egg. Moreover, the ability of males to produce germ cells and reproduce offspring for almost their entire lives after maturity also gives them a significantly greater chance of producing offspring than females. Throughout the long history of mankind, males who live long enough to have multiple mates have tended to produce more offspring than a single mate. In contrast, females are extremely limited in the number of offspring they can produce due to the need to nurture their young. For example, human females produce no more than 520 mature germ cells in less than 40 years of reproductive life, from the time they reach puberty, when they begin to ovulate and become capable of producing offspring, to the time they stop ovulating and become infertile at menopause. Moreover, for each pregnancy and birth, the number of mature germ cells produced by a woman decreases by 3-4% of the total number of mature germ cells due to the cessation of ovulation during pregnancy and breastfeeding (the period of time after pregnancy and breastfeeding when ovulation does not occur is about 15 menstrual cycles, which is more than one year). Even if a female gives birth and breastfeeds uninterruptedly during her reproductive years, the maximum total number of opportunities to produce offspring does not exceed 30. Thus, the relative infinity of opportunities for males to reproduce offspring and the absolute finiteness of opportunities for females to reproduce offspring creates a huge contrast (which is particularly prominent in humans as well as other primates) and to some extent lays the basis for differences in behavioral traits between the sexes. In the case of males, the theoretically unlimited number of offspring both motivates behavior that actively creates conditions for acquiring the resources to raise as many offspring as possible and inhibits behavior that focuses too much on one of the theoretically unlimited number of offspring. As a result, in the activity of breeding offspring, males protect their young more by training their offspring in the behaviors of capturing prey, fending off predators, and escaping from dangers, and less by taking specific protective measures to guard against specific injuries to their offspring. In other words, rather than reducing the survival risk of their offspring by restricting their risk-taking activities, males increase the survival probability of their offspring by enhancing their adaptive and precautionary abilities. Such a behavioral trait can also be understood to mean that males are looking at the long-term effects to safeguard the survival probability of their offspring. This can be understood through certain academic studies or films that have taken a close look at animal behavior, such as the Japanese film “Fox Tales” (Japanese title “Tales of the Northern Foxes”), shot in the 1970s, which shows that paternal males place more emphasis on training and cultivating their cubs in predation, aggression, and defense, and are less concerned with the specific protection of their cubs. Particularly striking is the behavior of the fathering male fox in driving the already motherless cubs away from their homes in a determined manner after the fox cubs have acquired the ability to hunt for food and basic self-defense. It is this pattern of outward risk-taking, aggression, and rational defense of the cubs by males that ensures that their offspring will be able to sustain the lineage in the natural competition of the law of the forest. In contrast, because of the finite number of offspring as determined by the female’s ability to breed offspring, she will seek to maximize the margin of safety in her breeding activities to ensure that each of the offspring she breeds will have as safe an environment as possible in which to survive and grow and develop into an adult individual, so that she will have as many individuals of her offspring as possible who can reproduce. Therefore, females take more protective measures to keep each offspring safe, and these patterns of behavior in pursuit of excessive security may have reached their peak in humans. Unlike males, females do not increase the survivability of their offspring by increasing their ability to cope with frustrating risks, but rather they secure their offspring by reducing the risk factors in their environment, i.e., females are focused on current effects to increase the probability of survival of their offspring. In real life every mother provides her children with protection that is not necessary to a greater or lesser extent. For example, many mothers sterilize the nipple with boiling water or even alcohol a number of times before feeding their infants in order to ensure that their children do not develop gastrointestinal infections. Such behavior in itself goes beyond the need for infant dietary safety, and the lack of necessary microbial stimulation of the infant’s gastrointestinal tract caused by excessive cleanliness as a standard may instead lower the infant’s digestive tract resistance and make it more susceptible to digestive tract diseases later in life. There are also many mothers who, out of a misconception that changes in ambient temperature will adversely affect the health of their children, tend to dress their children in excessively thick clothing, which reduces the children’s ability to regulate their own body temperature and their ability to withstand the cold.