The dominant animal—as determined in ritualized or occasionally in earnest combat—is called “alpha” after the first letter of the Greek alphabet. After alpha comes beta, then gamma, delta, zeta, eta … and so on down to omega, the last letter of the Greek alphabet. Most often, alpha lords it over beta, who makes appropriate indications of submission; beta over gamma, gamma over delta, and so on down the hierarchy.* The alpha male might exhibit dominance behavior in the male hierarchy 100% of the time, the omega male or males 0% of the time, with those in between showing intermediate frequencies
Apart from the dubious intrinsic satisfaction of intimidating others, high rank often carries with it certain practical benefits—the privilege of dining first and from the choicest morsels, say, or the right to have sex with whomever strikes your fancy. The most passionate enthusiasts of dominance hierarchies are almost always the males, although loosely parallel female dominance hierarchies occur in many species Males generally dominate all females and all juveniles. Among the comparatively rare species in which females sometimes dominate males are the vervet monkeys, the very same who keep their cool when overcrowded.
While privileged access to desirable females is not the invariable accompaniment of high rank, it is a frequent benefit In a population of mice, the top third of the hierarchy was responsible for 92% of the inseminations. In a study of elephant seals, the bulls in the top 6% of the dominance hierarchy impregnated 88% of the cows.6 High-ranking males often work hard to prevent lower-ranking males from inseminating the females. Females sometimes act to incite rivalry among the males.7 If the dominant males are going to father almost all the children, then clearly there’s a major selective advantage to being a dominant male. Whatever inherited qualities predispose to accomplishing, maintaining, and enjoying dominance will swiftly be established throughout the population—or at least among the males. Social and individual constitutions will be reconfigured by evolution to this end. Indeed, there seem to be parts of the brain in charge of dominance behavior.8
Promotion in rank does not usually occur because of community social work or fighting off invaders. Promotion comes mainly from combat within the group—mainly ritualized, sometimes real. Darwin clearly understood how natural selection might bring this about:The law of battle for the possession of the female appears to prevail throughout the whole great class of mammals. Most naturalists will admit that the greater size, strength, courage, and pugnacity of the male, his special weapons of offence, as well as his special means of defence, have been acquired or modified through that form of selection which I have called sexual. This does not depend on any superiority in the general struggle for life, but on certain individuals of one sex, generally the males, being successful in conquering other males, and leaving a larger number of offspring to inherit their superiority than do the less successful males.9
If you’re a second lieutenant in the hierarchy and wish to be promoted, you challenge your first lieutenant; he would challenge his captain; he his major; and so on, up the ladder. In this respect at least, animal dominance hierarchies and human military hierarchies differ. Perhaps certain dog-eat-dog corporate hierarchies provide a better parallel. In the case of a successful challenge, the two animals sometimes exchange status, silver bars for gold. Animals weakened by disease, injury, or age are generally broken to the ranks.
“This town ain’t big enough for the both of us” isn’t the way dominance hierarchies usually work. Faced with a testy alpha male, you have another option besides fight or flight. You can submit. Almost everybody does. Subordinate males ingratiate themselves to those at the top of the hierarchy through incessant bowing and scraping. From their proximity to power those next in rank tend to gain access to food and to females, the leavings of the alphas. Sometimes dominant males are so busy with their police functions that those lower in the hierarchy can arrange sexual trysts that never would have been permitted had the alphas been less preoccupied. Surreptitious fertilization of females when the alpha male isn’t looking is called “kleptogamy.” “Stolen kisses” has something of the same flavor. So being alpha is only one strategy for males to continue their lines. Being beta or gamma with an inclination for kleptogamy is also a strategy. There are others.
An unambiguous, well-defined dominance hierarchy minimizes violence. There’s plenty of threat, intimidation, and ritual submission, but not much bodily harm. Violence does occur when the rank order is uncertain or is in a state of flux. When young males attempt to establish their place in the hierarchy, or when there’s a struggle at the top for alpha status, then there can be serious injuries, even death by combat. But if you don’t mind constantly subordinating yourself to those of superior rank, dominance hierarchies provide a peaceful and ritualized environment with few surprises. Perhaps this is part of the appeal for those humans drawn to the religious, academic, political, police, and corporate hierarchies, and the military establishment in peacetime. Whatever inconveniences hierarchy may impose are offset by the resulting social stability. The price may be paid in anxiety—anxiety about offending those of higher rank, being perceived as insufficiently deferential, forgetting yourself, committing lèse-majesté.
In maintaining the dominance hierarchy, all conflicts (chiefly ritual or symbolic combat) are between animals who know each other well. But xenophobic intraspecific aggression is different, occurring between animals with no perceived bonds, relationships, or even familiarity. It’s an encounter with strange-smelling aliens, and the circumstance most likely to lead to casualties and deaths.
When an unfamiliar mouse arrives, rats drop what they’re doing and attack it—dominant rats attacking the intruder’s back and frequently mounting it in the process, while subordinate rats attack the intruder’s flanks and rarely mount it. Each in his own way.10 Among mice living in small groups, those at the top of the hierarchy tend to be most active in scuffling, intimidating, and fighting, in reacting to novelty, and in fathering baby mice. They also have sleeker coats than the subordinate males. But when it comes to fighting mice of another group,11 suddenly democratic forms come into play and the subordinates fight side-by-side with the alphas.*
The simplest geometry of a dominance hierarchy is linear or straight-line. This is what we’ve been describing. The private defers to the corporal, the corporal to the sergeant (and if you look more closely, there are various hyperfine grades of privates, corporals, and sergeants), the sergeant to the second lieutenant, and so on, up through first lieutenant, captain, major, lieutenant colonel, colonel, brigadier general, major general, lieutenant general, plain old general, and general of the army or field marshal. The military establishments of different nations have different names for the various ranks, but the basic idea is the same: Everyone knows his rank. A currency of deference is offered by subordinate to superior. Homage is paid.
Linear hierarchies are a mode of social organization readily observable in domestic fowl, which is where the phrase “pecking order” originates. It’s especially clear-cut among the hens. (In mammals the pecking order is often the chief fact of male social life.) Again, the alpha hen pecks beta and everybody lower; beta pecks gamma and everybody lower; and so on down the hierarchy to poor omega, who has no one at all to peck. The high-ranking males try to sexually monopolize the hens, but sometimes they fail. Cocks dominate hens except on rare occasions; the word “henpecked” refers to the exceptions and comes from everyday observation of barnyard life.