1. Introduction

Polygamy has long been a part of human history. Polygamy used to be the most universal marriage system—among 849 investigated cultures, about 85% appear to be polygamic [1]. But since the arrival of seventeen century, many countries started to erect laws to make polygamy illegal. Currently, polygamy is only permitted in 58 out of 200 sovereign states. Some scholars claim that the equality between man and woman can be promoted by monogamy, which render a context to trust and intimacy, and thus offers a solid foundation for social progress [2]. However, through my observation, our current marriage system is not flawless, presenting numerous social problems like an increasing divorce rate, a decreasing birth rate, the growing problem of infidelity. For example, according to sociologist Philip N. C. [3], China’s divorce rate has been radically increased from 0.35% to 2.0% since 1980 till 2010. Moreover, the U.S. birth rate has fallen 20% since 2007 [4]. These beg the question: is monogamy a social progress or a suppression of human nature? In this work, we have analyzed males’ and females’ priorities and preferences in mating. However, this work puts emphasis on what women can obtain through marriage rather than men. Therefore, what men can obtain through marriage except for carrying on the family line is omitted in this work.

2. Male Short-term Mating Strategy

What is the nature of human mating psychology? How do mating strategy vary between long-term and short-term relationships, and between males and females? Due to lower obligated parental investment, the short-term mating strategy for male should focus on ‘quantity’ instead of ‘quality’. Initially, the necessary cost for a male to mate or have an offspring is relatively low: a male generally can generate about 525 billions of sperms during his lifetime, and they only produce fewer than 1.2 billions of sperms in a single ejaculation. However, this behavior is not free of risks. For example, if a male dates with females in the same social circle, it could be possible that they exchange their information behind, earning him a negative reputation. Additionally, sexually transmitted diseases (STD) could be a considerable risk in short-term relationship. As a part of short-term relation, casual sex is sometimes conducted without condom protection, which may lead to STDs. According to WHO (World Health Organization) [5], sexual and reproductive health can be influenced tremendously by STDs, such as stigmatization, infertility, cancers, and pregnancy complications and increasing risk of HIV. If aforementioned risks can be avoided, pursuing multiple mates can be an optimal evolutionary strategy for men. This is because different cost-benefit trade-offs indicate that men need to pursue more mates on average than women [6]. However, this statement assumes a prerequisite that a majority of men do well in short-term mating. For those men who do not have traits (see female mating strategy) women prefer in short-term relationships, the effort they make in short-term relationships outweighs their gain. In such a competitive environment, some males can gain plenty of benefits while some males would be absolute losers. Therefore, in modern society, male should pay more attention to careers to which offer them considerable material benefits, self-improvement, and chances of success in a stiff-competition market [6]. In other words, males should devote to improve their sexual market value, and mate with certain number of females based on their competency in sexual market to balance costs and benefits.

3. Female Short-term Mating Strategy

The mating strategy for females is different. Initially, the direct cost of a single sex with a male for a female is comparably huge. Physiologically, only 300 to 400 will be ovulated during a female's reproductive lifetime. Therefore, compared to males’ sperms, females’ eggs are precious, which has selected for females to be cautious when choosing an excellent mate for pregnant, valuing ‘quality’ over ‘quantity’ of males in short term relationship. When females are choosing mates, there are two types of cues that females prefer: (a) attributes that tend to signal qualities of a “good provider”, and (b) attributes suggesting that an individual may have “good genes” [7]. A study is conducted to show how females’ preference of these two types of males between short-term and long-term relationships. Kelly and Dunbar [8] had 120 subjects (ages 18 to 55 years) rate eight profiles of imaginary male personalities designed to portray the presence or absence of the qualities of altruism or bravery. The study indicates that women prefer altruistic men for friendships and long-term relationships. In contrast, the study reports that men, with traits such as braveness, non-altruism, and willingness for risk, are more likely to be favor by women in short-term relationships (i.e., flings or affairs). In other studies, dominant males are more likely to be found their sexual attractiveness by females, no matter whether they are favor of those males or not [9]. In these studies, the altruistic males tend to fit into type (a) and are thus being favored by females in long-term relationship as a “good provider”. Those males who show male dominance and braveness fit into type (b), and females tend to be in short-term relationships with these males. This conclusion is also supported by the model suggested by Gangestad in 2000. To females, short-term mates or extra mates should offer genetic benefits that are often unavailable from long-term mates. Additionally, when males are assessed by females for potential short-term relationships, Scheib [10] claimed that females weight more portions on physical attractiveness and power.

4. Female Long-term Strategy in Mating and Marriage

Understanding mating strategies for males and females, then, in long term relationships we can analyze how these strategies fit into marriage systems, polygamy and monogamy. For females, according to SST (sexual strategy theory), men are estimated by women for underlying long-term mates through men’s performance in the short-term relationships. And the traits we have discussed that females prefer in long-term relationships include altruism, risk-averseness, or non-braveness, etc. Once females discover these traits as a “good provider”, they start to consider these males as potential mates. However, in modern society, this strategy can vary among females due to the variation in their circumstances. Females base on their own needs to choosing mates in a trade-off between genetic benefits and material benefits. If a woman can gain both genetic benefits and material benefits on a man, it is reasonable to assume that monogamy can benefit a woman the most. If a woman cannot gain both genetic benefits and material benefits on a man, polygamy sometimes would be a better choice than monogamy. A good example could be a polygamous society. As we have discussed, female reproduction is limited by survival resources, shelters, and necessity to care a child. If we define a higher status male has more recourses than a lower social male, females prefer the former one. Thus, female often prefer to be one of co-wives of a prosperous male than an only wife of a poor male [11, 12]. In some developing countries, many females are economically independent on males and therefore have few needs to seek for material benefits on a male. If females can considerably benefit by mating with males that carry better genes, they should choose these males as long-term mates or they should have engaged in short-term mating with males who had such indicators, even if it meant “trading-off” or risking the loss of material benefits they could have garnered from a long-term mate [6].

5. Conclusion

For males, they should try their best to mate with women as more as possible in short-term mating, whereas they should allocate sufficient energy, time, and other resources for long-term mating (including mate guarding) and parental investment, to attract and retain one mate and derive the benefits of parental investment [6]. For females, they should mate with men who have attribute suggesting signal of “good genes” in short-term mating, and select men who tend to be a “good provider” in long-term mating. In terms of marriage, women need to consider whether they can obtain both genetic and material benefits in one man or not. If not, they should take account of maintaining a relationship with men while engaging in marriage with one man in marriage. In short, let me quote a sentence from G.A. Schuiling: “For humans, the optimal evolutionary strategy is monogamy when necessary, polygamy when possible.”