1. Introduction

Humans are constantly evolving. Whether it is reproduction, courtship, socialization, parenting, etc., humans today are making different choices than their ancestors did 10 million years ago. Each evolutionary change in human choice is the best choice for survival and reproduction that humans have made at each time and different culture. The focus of this paper will be on the evolution of the psychological mechanisms of human parenting styles. The original parenting division of labor patterns of human ancestors 10 million years ago will be traced, and the reasons that led to different parenting styles in modern societies, comparing the West and East, will be analyzed. What’s more, elaboration on how these different mechanisms lead to the development of various parenting styles that function in different cultural contexts and times will also be provided in this paper.

2. Mechanism 1: Shifting Male Efforts from Seeking Mates to Paternal Investment

In the lengthy history of humanity, most human societies allowed polygamous mating strategies. A male had more spouses than others if he had hunting skill (primitive society) , social standing, noble descent, or riches (feudal society). For instance, the autocratic leaders of chiefdoms, empires, and early states ranging from Tonga to China married (or kept as concubines) 100 or more girls/women continually. It was a really common phenomenon that is a combination of male and female mating decisions [1].

Trivers proposed a concept called parental investment in 1972, which means parents expend their energy or resources on their offspring (look after/care) such as hatching and feeding. The more investment parents put in, the more possible offspring survival rates are [2]. The big differences between the mating strategies of males and females are due to the difference in offspring investment.

Mothers invest more in children because they have greater costs, such as 10-month pregnancy, lactation, ovaries, uterus. In this case, females are very careful when choosing a mate. Males have more sperm and a longer reproductive age. Also, they are physically strong and aggressive. Thus, The male is the competitor and the females always make the choice. Men may be capable of having a lot more kids than women. However, based on market dynamics and the sex ratio, men will experience a greater reproductive skew than women. Then the men's difference between each other (variance) is greater than the women's. Male need to compete with mating. In societies where males varied substantially in status and women preferred males who had high social status, this led to intra-sexual competition between men becoming fierce. Low-status men would be shut out from mating so they would need to spend more investment to find and attract mates than on raising offspring.

However, with the increase of social inequalities (means the wealthy take away opportunities for low-status males to form pair bonds) and complexity in human history, the group-level of normative monogamous marriage increase because a higher rate of polygynous marriage decline a society's competitive success and overall benefits. Humans will consider the group-beneficial effects such as reduction in crime rate, and gender inequality.

The result was increases in paternal investment and improved childhood outcomes. Low-status males have more opportunity to marry, save, and make long-term investments because of normative monogamy. Instead of becoming risk-taking criminals or substance abusers, these individuals focus their skills and labor into long-term investments in marriage and parenthood. Compared to their risk-taking, status-seeking mindsets, their pair-bonding and paternal investment psychologies are tapped and exploited substantially more. Normative monogamy increases the cost of finding new partners for married high-status guys, which causes them to focus more on enhancing the quality of their offspring rather than finding new partners [3].

3. Mechanism 2: The Difference between Asian and Western Parents' Investment in Their Children

Parents' investment in their children has a huge impact on their children's lives. Parents from different cultures have different patterns of investment in their children. Asian parents pay relatively more attention to their children's academic achievements and push them to obtain the skills and certificates they need for their future life, while Western parents relatively prefer to cultivate their children's self-confidence and independence. Eastern parents have more requirements for their children, while Western parents are more willing to give their children free space to grow up. HSBC Bank USA did a survey of parents in different countries. They recorded parents in 15 countries, including China, the United States, the United Kingdom, the United Arab Emirates, and India, about their children's investment in education funds and time, as well as their views on studying abroad. The survey shows that 82% of parents in the world are willing to sacrifice their time for their children's success, but parents in Hong Kong, Taiwan, and the Chinese Mainland are the most willing to sacrifice holidays and entertainment time to accompany their children. In contrast, Western parents seem less concerned about their children's education [4].

Western parenting methods usually allow children to express their feelings and opinions openly with others and learn to communicate properly with others. Parents do not force children to make decisions and teach them independence at an early age. However, due to this reason, children in the West are accustomed to making decisions by themselves and disregard their parents’ advice, which could result in children lacking self-control and forming unhealthy behaviors due to their freedom.

Asian parents have a more protective approach to education. Parents often help their children with many things, but due to excessive parental intervention, children may not perform well when faced with difficulties alone. In addition, Asian parents tend to place high academic demands on their children. In 2011, author Amy Chua explained how she raised her daughter in a "traditional Chinese" way in her memoir "Battle Hymn of the Tiger Mother," noting that she had strict control over her daughter, and demanded academic success, and did a lot of practice for this. Computer games, television, and dating were strictly prohibited. This book aroused a lot of attention and controversy. Amy Chua's education method is called authoritarian education，which tends to make children too stressed and have psychological problems such as depression and anxiety [5].

One of the reasons for this difference in investment in children between Asian and Western countries is history and culture. For example, China, which has a history of 5,000 years and has been influenced by feudalism for a long time, is more conservative, lacks adventurous spirit, and lacks innovative ideas. Chinese parents tend to impose strict discipline on their children, let them learn to obey, and hope that their children will get good achievements and stable jobs. In contrast, Western countries, such as the United States, are immigrant countries with a short history, and under the influence of multicultural values, old ideas are rarely preserved, and new ideas are easily accepted and developed without restriction. Influenced by multiple cultures and multiple values, it can accept new ideas and cultures faster and without restrictions [6].

4. Mechanism 3: Owing to the Change from Big Family to Small House, Relatives Help Less for Raising Kids

Different Family structures can result in different parenting styles. Multigenerational for this paper is defined as more than two generations living in the same home, or grandparents living with grandchildren under the age of 25. In contrast, a monogenerational family structure for this paper is defined as a parent or parents raising children alone. In a monogenerational structure, parents need to give more time to care for their children because they receive less help from their families. Conversely, parents do not need to spend more time caring for their children in a multigenerational family, since they can receive more help from their family members.

The traditional Chinese family that raises children is the multigenerational family. This is a result of the interplay of cultural and economic factors. Buddhism is the dominant faith in China. In the Buddhist Sutra of Good Life, it is mentioned that “The son should honor his parents with five things: First, he should make offerings so that there is no lack of them; second, he should first confess to his parents whatever he does; third, he should be obedient to his parents and not disobey them; fourth, he should not dare to disobey his parents' righteous orders; fifth, he should continue his parents' righteous work”[7]. People are taught to be obedient to their parents and respect their elders. Living with one's parents allows one to take better care of them and to do one's filial duty in the last days of their life. When it comes to economic factors, it is necessary to mention the term "Sandwich Generation". The “Sandwich Generation'' in this paper is defined as a select group of people (especially ages 40-56) who, for a number of reasons, need to care for their young children or elderly parents [8].

Since grandparents live in the home, parents do not have to give as much time to take care of their children when they are working. For women with jobs, leaving children with grandparents is the best option. Since Chinese women consider female work as a form of social acceptance, few choose full-time motherhood. Therefore, having grandparents help them with childcare is the most feasible way. Because of the culture, raising children becomes the responsibility of parents along with grandparents [9]. While having grandparents in the home to care for children together can reduce the burden on parents, grandparents can disagree on how to raise their children. For example, grandparents may dote on their grandchildren, making it difficult for parents to discipline their children as they wish. This can make it more difficult to raise children. While parents think grandparents overindulge their children, grandparents also think parents are too strict with their children's education [9]. These have to do with the traditional Chinese concept that older Chinese people always aspire to spend their later years with their grandchildren eating candy and playing leisurely [9]. Also, among the grandparents, the grandmother prefers to spend more time raising her grandchildren. Humans are not capable of feeding themselves after weaning age because they do not have the ability to obtain their own food. Thus, women nearing the end of their fertility can increase the survival rate of their offspring by helping young grandchildren [10]. Women who can afford to raise their own grandchildren can help their offspring get a higher survival rate. Also, their vitality can be passed on to their own offspring so that their offspring also have the genes for vitality.

In America, the monogenerational family structure is more common in society. Parents thus find it harder to get family support from their grandparents. However, In modern American society, multigenerational relationships have become important [11]. As divorce rates rise, support from family becomes increasingly essential in the monogenerational family. In poor areas of the United States, it is common for multiple generations to live together. Multi-generational families can help each other internally and reduce unnecessary waste, like food. Further, young mothers may not be able to ensure that their children have a secure and quality environment [12]. Young parents need to go out to work because they don't have enough savings and income, which can lead to children not getting a stable life. Parents' inexperience in parenting may also affect the child's mental development. Getting help from grandparents can reduce parents’ need to spend extra time caring for their children and help them get an excellent developmental environment. Children can also get extra companionship from grandparent care.

Due to changes in the economy, parents are becoming more willing to take care of their children themselves. This has led to parents giving more time to care for their own children. Because of the decrease in full-time mothers, fathers began to invest more time in the family in order to better raise their children. When fathers are more willing to nurture their children, the survival rate of the children increases greatly, and thus the gene for willingness to nurture begins to be passed on.

5. Mechanism 4: More Job Opportunities for Women Which Leads to the Raising Status of Women

During the Industrial Revolution (1740-1860), women in the Western world gained expanded employment opportunities, the ability to engage in business and work, and greater freedom outside of the household. In contrast, Chinese women were compelled to bind their feet until the Republic of China era (1912-1949). This practice, known as foot-binding, inflicted physical and psychological suffering primarily on young girls, leaving lasting impacts throughout their lives. During the Republican period, work suitable for women began to appear and the foot-binding practice gradually declined [13]. It was not until the reform and opening up period that women's work options increased, except in rural areas, with a significantly higher proportion of women commercial service workers, professionals and technicians compared to men, as well as some rural women achieving a change in economic status. The role of women researchers in advancing the progress of national science and technology is a pivotal force that not only drives innovation but also constitutes an integral component of the entire nation's socio-economic fabric [14].

In 2014, China had 40.47% of the whole human resources in science and technology[KM4]. In terms of growth, the growth rate of women exceeded the overall growth rate in all periods, and it continues to increase.

In the 1970s, the amount of human resources in science and technology in China was only 0.19%, of which the amount of female’s was only 0.1%; until 2014, the amount of the whole China has reached 5.57%, of which the amount of female’s reached 2.17% in women and 4.45% in all people [15].

According to survey data from three countries, women spend more time on housework than men. Although some studies in recent years have shown that men and women have shared more housework than in the past [16][17], women's housework time has not decreased significantly.

In conclusion, the increase in women's work options meant that women do not have to spend all their time at home and can be unencumbered by their families, this led to the status of women's growth.

6. Mechanism 5: Female Independence Greatly Increases the Divorce Rate, and the Emergence of Single-Parent Families Also Brings Different Investment

From an evolutionary psychological perspective, the pattern of parenting style has also evolved and varies between cultures due to the rise of women's status. How is parenting style related to women's status? “In the 1980s, as more wives entered the job force, their proportional contributions to family income climbed [18].” Labor force has brought the opportunity to let women have their own income. Stacy J. Rogers and Danelle D. Deboer has suggested that, “Wives might be inspired to reform power dynamics, the division of responsibilities in the family when they have access to more resources].” [19], Before women worked, the majority of the family's resources came from men, so women were more dependent on men financially. However, when women have more access to economic resources and are less financially dependent on men, they have more courage and capital to change their marital status, and divorce will become an easier possible choice. Around the time after the Second Industrial Revolution which is the period from the 1870 to 1914, when electricity was widely used on a large scale. The female employment rate has been at a low level until and just after the second industrial revolution. For example, “in 1850, men accounted for 76.4% of employment in manufactures, while women accounted for only 23.6%. The male employment rate was seven times higher than the female employment rate” [20]. What’s more, back to the middle of the twentieth century, based on data, the divorce data shows the divorce rate per 1.5 million marriages is 2% [21]. It is evident that the marriage divorce rate in the United States was as low as the female employment rate in the last century. The economic resources of society are largely controlled by men, and most women have barely any job opportunities or economic resources. So women are the most stable and appropriate choice to stay married, whether in life or financially. Therefore, after the Industrial Revolution in the United States, the main family composition was the two parent family, and single parent family was not a common thing. “During the middle to the twentieth century, most families with children were called breadwinner-homemaker families, which is a two-parent family consisting of a father and a mother, and women were responsible for nursing the children at home and men needed to go out to earn money [22].” In the vast majority of households, two-parent families were in the majority, and women's main responsibility continues to be to stay home and nurture their children. Mothers cared for and raised children, and fathers were generally less invested in their children than women because fathers were busy providing for their families. Women were still content to achieve their fulfillment and mission by nursing their children.

As society evolves and laws improve, women are more likely to enter school and start working. “The historically increasing divorce rate has made paid work more desirable for mothers concerned about losing most or all of their husband's earnings due to divorce [22].” As women become more socially connected and financially independent and independent-minded, the function of a man to provide for his family is no longer a skill unique to men. And the loss of the function as a father caused by men working outside for long periods of time makes the importance of men in marriage much less. When men lose these functions in the family, it makes marriage no longer a necessity for women.Single parenthood becomes a better choice for them. Marcassa suggested that, according to the analysis, “American family structure has undergone a significant transformation. The percentage of all children living in the family with two parents who both never divorce has dropped from 73% to 57% since 1960 to 2009 [22][23][24].” The increase in single-parent families means that parenting style will also be very different from what it once was. In the 19th and 20th centuries, although fathers were not as fully involved as mothers in the task of raising children, the two-parent family structure still gave children enough security and stability. The father would bring in a steady financial income outside the home, and the mother would have a steady and constant presence at home. This allows the family to run and care for the children with two people taking on the tasks together. Although a hundred years ago the majority of fathers were responsible only for earning money and mothers only for parenting. However, after a divorce, the distribution of responsibilities that parents have to bear may be redistributed. The parent with whom the children will follow may have more responsibilities than they would have had before the divorce. Alan Booth and Paul R. Amato had concluded that “The happiness of the divorces and kids will be lower [25].” Issar Daryanai, Jessica L. Hamilton, Lyn Y. Abramson, and Lauren B. Alloy1 have suggested that “Women are generally less educated than men and earn lower wages than men due to the discrimination against women in society. Therefore, a single mother's family facing the probability of destitution is much greater than a two-parent family [26][27]. Single-parent families face much greater problems and risks than two-parent families. When either parent faces financial problems or physical problems, there is another person who can support them. But if the parent who has custody of the child faces any financial or physical problems, the blow to that single-parent family will be enormous. So when single mothers face various problems in their lives, their care and patience for their children will be greatly diminished. “Compared to children who lived with both parents, children of single parents had a more distant relationship with their parents and a perception of them as being authoritarian. While communication and trust work better within two parents' families [28].” They need to worry about their children's safety, physical problems, but also have to deal with economic and environmental pressures, so strict discipline and control becomes a more appropriate parenting style for them to maintain their authority. Especially if the adolescent child is living with a single mother or single father, the child's rebellious and volatile emotions are difficult to notice and care for. Thus, one of the most common types of parenting styles in single-parent families is strict discipline and lack of communication with the child. Whereas in a two-parent family they can share more evenly the economic and parenting pressures, so their financial and physical situation will be more stable. What's more, the task of earning and parenting can be shared by two people. When they do not have too much stress and suffering, they will naturally be more patient with their children and will give more time and companionship to the kids. In the end, it is not true that the parenting style of a single-parent family must be strict and detached, while the parenting style of a two-parent family must be gentle and open. Whether or not the father and mother are divorced or together does not really determine the parenting style, but rather the mother and father share equally and less stressfully take the responsibilities of making ends meet and raising the children will have a greater impact on parenting styles. For example, a single mother needs to take care of her children and work, but having a father who is willing to pay support on time and be there for the children can also bring emotional stability and care to the children. A two-parent family that is not divorced but has two parents who only know how to earn money may also not provide enough companionship for the children and then form a strictly authoritarian parenting style.

7. Conclusion

Since monogamy can provide more benefits for men, more men are choosing to invest in the long-term investment of raising children. Two-parent families can give their children more time and companionship than single-parent families. As women become more financially and mentally independent and their status increases, women are no longer dependent on men alone for their livelihood. To reduce the divorce rate, it seems to be a good option for fathers to give more time to their children. With the industrial revolution, women gradually put into the field of science and technology, growing the status of women. However, this did not mean that women's time for housework decreased, but housework began to be shared by women and men. In comparing child-rearing styles in Western and Asian countries, Asian parents are more willing to sacrifice their time off to be with their children. This result is caused by the historical and cultural differences between the two regions. Asian parents are more concerned with their children's academic performance to ensure a stable future for their children. In contrast, Western parents prefer to foster their children's independence and let them solve problems independently. Grandparents in Asia are more willing to participate in child-rearing. However, conflicting ideas about physical health and child-rearing led grandparents to spend less time raising their grandchildren, and fathers investing more time in the family could increase child survival rates.