One of the primary concepts that must be understood to understand the sexual market place is the concept of Hypergamy.
Hypergamy is the female preference to mate with a top-tier high status mate.
This definition is inadaquate to explain the degree to which hypergamy influences mate selection.
The graphic above is commonly shared in the manosphere to visually explain hypergamy. Effectively, men, who are not hypergamous by nature, can happily pair with someone of equal, higher, or slightly lower status than themselves. Women are not so egalitarian in their mate selection. According to this image, women are attracted to the top 30% of men, and consider anything less than a 7 to be undesirable. A lower tier women, say a 3 in terms of status and attractiveness, would consider a man who is a 6 to be unarousing.
To the male brain this seems ludicrous, yet there is a certain logic to this biological programming. Sperm is plentiful while eggs are scarse. Supply and demand dictate that women command a higher value and can afford to be more selective. It makes sense: a man is able to reproduce as often as he can ejaculate, whereas a woman can only reproduce once every roughly nine months. Further, women assume greater risk in becoming pregnant. Men who impregnate a woman do not lose any of their physical ability, whereas women become increasingly vulnerable as their pregnancy progresses. A woman who mates must have reasonable assurance that their mate will have the ability to provide physical safety and sustinance not just for himself, but for her as well during her time of vulnerability. Thus, mating with a man who has demonstrated high-status is preferential to mating with a man of meager means.
We observe this behavior in the animal kingdom as well as in some societies where monogamy is not culturally normative. In both cases, the males of high status get to mate with the most females whereas the low status males are left out. This leaving lower status men out of the sexual market place has been observed to have a destabilizing effect on society.
Marriage as an institution has served to curb the effects of this mate selection preference. Institutionalizing mating in legal terms, licit and illicit sexual relations could be determined and inforced. Even in highly polygamous societies, typically a dowry payment was required to marry someone's daughter. This sort of financial barrier supresses the ability for a small handful of men to aquire all the women and helps to distribute mates more evenly across the men in a society. The Islamic limitation of men marrying no more than four wives also serves as way of limiting a few top tier men from monopolyzing all the women. Monogamy is the most severe regulation of hypergamy in the SMP. Limiting both men and women to a single mate ensures, in theory, that there will be mates available to all who seek them.
I say in theory because regulation does not alter desire. A man who is a 3 is still unlikely to win the affection of a woman who is likewise a 3. It is quite possible that the woman would rather remain unmarried than marry a man she does not desire.
The ramifications of hypergamy are far reaching. Understanding it serves as a key of sorts to unlocking and understanding male and female intersexual dynamics.