Among many mammalian species, the dominant male, or alpha male, is the only one supposed to breed and have sexual intercourse. Lower-ranking males can occasionally sneak in and themselves gain access to females. But it's a forbidden act, and will likely be punished severely by the dominant male, if it comes to his attention. However, because even the most advanced species outside homo sapiens have no language or equivalent means to confer information, dominant males, as other members of any species other than homo sapiens, only know what they see themselves.
Human society isn't as extreme in structure as the societies of some species, in which only alpha males breed. But there is a typical tendency for alpha males to seek out as many sexual partners as possible, and genuine alpha males typically succeed to appropriate a much larger share of females than would be their "fair" allocation.
Human males who appropriate a disproportionate share of the females are nowadays not interested in making each of their conquests a permanent wife. The tendency is for a male to use a female a number of times, and then to discard her.
Therefore, in order to assess the degree of polygamous behavior of a certain man, we ought not to look at by how many females he is or has been bound into a permanent relationship at any given time, but solely at the number of different sexual partners he has ever had without getting married to.
For such a statistic, a one-night stand counts more than a lifelong exclusive relationship. It counts more because actually, in many human societies, it is easier to find a wife than a one-night stand (in all of the Middle East), and a man who marries is conceding much more than the one given permission for a single use.
A man who concedes to the conditions brought about by a marriage typically signs over to his wife much of his wealth and financial independence. Because this kind of behavior does require irrationality, there is, under ordinary circumstances, a high degree of reluctance on the part of men to be available for marriage. A marriage is a victory for the female partner, rather than a male conquest.
An alpha male, therefore, is defined as a man who gains access, or copulation rights, with as many women as possible, without allowing a woman the victory of becoming a man's wife.
Let's assume we have a group of 1000 men and 1000 women. Let's further assume that in this group, women have an average of 10 sexual partners during their life span. Of these, an average of 1.5 sexual relationships are with men who are their husbands. This then leaves an overall of 8500 sexual pairings to be counted in establishing our statistics.
My hypothesis is that some 50 men account for more than 5000 of these 8500 pairings.
Some men definitely are more popular with women than others. They are not just a bit more popular.
I assume that in any given society, some 80 percent of the women strive for just 5 percent of the men. But these 5 percent are chronically difficult to bind into permanent relationships, which is why most women, while being occasionally available to alpha males, also settle into permanent relationships with beta (just average and willing to marry) or gamma (below average, but willing to marry) specimens of the species.