It's applying pack-animal sensibilities to humans-in-groups behavior.
And it happens.
But I don't think that it is necessarily “natural” behavior. In fact, it leads to some really odd behavior on people's parts, trying to fit into these roles. Especially when they deal with people who don't fit into these roles.
People come together in groups for a number of reasons. Sometimes they are drawn together by some charismatic/strong personality. These are legitimate “Alpha/Beta” type hierarchical social structures, where one person is really the organizing force behind the group. But there's other reasons why people form groups. Sometimes they are drawn together by some common interest (could be writing, or gaming, or simply liking the same bar). Sometimes, they are shoved together by the vagaries of the job market, or family, or tragedy, or living in the same neighborhood. There's no reason why these sorts of group interactions need to be governed by a leader/pack mentality. And yet, very often they are.
To some extent, I think we can point at Pop Psychology as giving this legitimacy. We're told that human social structures are based on an Alpha/Beta dichotomy, that this is the natural order of things. We're told that the rules of pack behavior, of dominance and submission, are the rules of human behavior. We're told this, and we believe this, because there are cases where it is true, and then we apply that universally. And that legitimizes all sorts of weirdness.
It legitimizes pointless power struggles. It legitimizes abusive, humiliating, and hurtful behavior. It legitimizes abrogation of one's responsibility to think and act independently. We've applied this model to business relationships, to employer/employee relationships, to political interactions (see the Republican's attacks against Arlen Spector and Christine Whitman, and the Democrat's attack on Joe Lieberman), to the interactions between countries (the way we handled the first 3 months of post-Saddam Iraq is a prime example). And we've applied it to more intimate social situations: families and groups of friends.
And worst of all, it reduces people from persons to roles, making their individuality subservient to their position, and dictating one's behavior toward any given person based on her/his place in the hierarchy. And there's only three roles: Alpha/leader, Beta/follower, and the ephemeral role of Challenger.
Anyone who isn't a Leader or a Follower is, by definition according to the rules of the game, a Challanger, someone aspiring to take leadership away from the Alpha and assume the Alpha position her/himself. Within the structure of the game, there are no other possibilities.
So to the Alpha, anyone who isn't a follower must be defeated. Shown her/his place. Failing to submit to the will of the leader can only be interpreted as a challenge for control of the group. Even if it isn't.
Because there's other roles, and combinations of roles. There's the Lone Wolf, the Rogue, the Free Thinker, the Devil's Advocate, the Anarchist, the Gadfly, and the Loki, and that's a necessarily incomplete list. There's tarot cards that show us representations of these people. There's myths of many cultures that give us archetypal descriptions of them. But there's no room for those in what has been constructed as the natural order of things. All those folks, and more, are Challengers, to be put down and turned into followers, or destroyed.
At whatever the cost.