But the bolded two aren’t natural - they are societal constructs.
No, they are natural instincts in human women and men. (explained further below)
Look at other mammal, including all other apes. Very few are monogamous. What is “natural” is the biggest, strongest male - i.e. the one with the best DNA - mates with the largest number of women he can protect. His whole life, the meaning of his life, is to protect his family group: his mates and kids. He spends every minute of his adult life in either the pursuit of mates or the protection of those mates, be it from predators or other males.
Females have no advantage to sleep around, because they have already chosen the best mate.
Males have every advantage to having multiple mates, as it spreads their DNA the furthest.
Females take almost every aspect of raising the young, except protection. The feed, they teach, they “raise”. The males have no part, except fending off predators and other males that often kill all the old male’s offspring
One has to understand that each species of animals has their own “system” that successfully spreads their genes. Humans, for example, will behave much differently than pack or herd animals.
There are two things that must occur in order to spread DNA. A male must mate with a female to produce an offspring, and that offspring must be successful. The rearing of offspring is a MUCH more involved and much longer process for humans than in any other animal, which makes the need to pair bond into long term relationships that much more important. It doesn’t imply, necessarily, that there is NO advantage to sleeping around with multiple women, but that there is a balance/struggle between the two different methods.
Its perfectly natural for women to not want their men to sleep around, and likewise its perfectly natural for men to want to sleep around but not let the women find out about it. Its also perfectly natural for the man to focus on one family and try to keep that family in tact.
Sure, each species has a system, family construct, or social organization, but each Family members are similar.
Look at Hominidae (great apes). Mountain Gorillas live in groups of about 9 individuals - 1 male, a few females and their offspring (Comparative socio-ecology of gorillas, Watts 1996). Lowland Gorillas live in similar groups, but with about 10 individuals. Female children leave the group at 9 - which isn’t too different than historic human patterns of 12-15. Male children don’t leave their group till 15! (Intra-specific variation in social organization of gorillas: implications for their social evolution, Yamagiwa 2003)
Chimps are really complex. From Jane Goodall: “There are several mating patterns seen in chimps. Some females in oestrus (period of sexual receptivity) are more attractive than others. A popular female may be accompanied by many or all the adult males of her community, with adolescents and juveniles tagging along. Or, the dominant male of the group may show possessive behaviour toward her, trying to prevent other males from mating with her. A third mating pattern is a consortship, during which a male persuades a female to accompany him to a peripheral part of the community range. If he can keep her there until the time of ovulation, he has a good chance of siring her child. Even low-ranking males can become fathers in this way, if they have the skill to lead a female away during her fertile period of her reproductive cycle.”
Orangutan males live alone 91% of their lives… Females take sole responsibility for raising kids (which leave at 7). Males have large territories (up to 4000 acres). Females have smaller, overlapping territories (up to 1000 acres). The male “owns” everything within his territory - food, water, females. The 9% of time he’s not alone is either spend protecting his territory from other Orangutans or mating with whoever lives in his territory. (Orangutan sexuality in the wild, Galdikas, 1981; Behavior of wild adolescent female orangutans, Galdikas, 1995)
The only other member of Hominidae are humans. 1,000,000 years ago, we would have been very close to one of these other Apes. Naturally, I’d suggest that males should have multiple mates because infant mortality is so high (in Gorillas it’s 38%). However, there’s this pesky civilization and domestication we’ve gone through. We’ve gotten infant mortality down to 0.52% (5.2 per 1000). More than 70x the number of human babies survive vs. Gorillas. People also spend more time at home than we used to - daughters were married off at 12 back in the day, which isn’t too different than Gorilla leaving their groups at 9.
It would be very interesting to have a study about pre-domesticated humans family structure. But, almost all records of that has been lost, and it’s not like there are any humans from 20,000 or 50,000 years ago around, nor time machines.
I still content that monogamy isn’t the natural way for humans to act, as extrapolated from the other members of the Hominidae family. 10,000+ years of domestication has destroyed most these urges though.
. That and 7,000,000,000 of us, with almost a 50:50 M:F split.