The problems intrinsic in this idea were that such groups could be potentially invaded by "selfish" individuals and thereby tip the scales in the opposite direction. A serious flaw with this argument was pointed out by Patrick Lockerby in stating "It is against the evolution of a group to allow the cheat to join. Cheaters are not joiners. Cheats 'break up the party."
From this point on the discussion degenerates further into an epicycles-style arrangement where concepts such as "kin selection" and all manner of extraneous rigor are introduced to make this explanation work.
However, if we take a step back we have to consider the obvious. The primary point, like it or not, is that altruism exists. So how did it evolve?
My solution is also an obvious answer. Altruism exists because there can be no "selfish" invaders in such a group, since without the group there are no survivors. In other words, the group itself is the only mechanism whereby such individuals can survive.
Once we accept this concept, then the degrees of altruism that can exist can take on a variety of forms.
The group is fundamental to the existence of such social individuals since they must obtain mates from an active population, so at some level, interacting with other members of the species is a given. In addition, genetic diversity must provide sufficient access to a variety of potential mates, so it isn't simply a matter of occasional contact.
Such pressures will invariably lead to closer territorial contacts and except for the largest animals, eventually result in groups forming up and potentially cooperating for food and/or protection. Much larger predators that are asocial, also tend to make the mating contact but seldom form groups for rearing, where the responsibility invariably falls to the female. It is my contention that such a form suggests that altruism isn't possible for such animals since they are demonstrably incapable of extending a social bond, even to their own offspring.
If a cooperative group experiences a higher success rate than those individuals that remain alone, then the selection pressure on being cooperative becomes a key element in the development of new group members. This is coupled with the likelihood that mating will occur between animals in a group much more readily than with outsiders.
Once such a group succeeds, the group itself becomes the pivotal element which ensures survival of its members. In short, there is zero survival value to an animal that is NOT a member of the group. Once this occurs, participation in the group becomes a matter of overriding importance causing many members to willingly give up their perogative for reproduction simply for the opportunity to be in the group and potentially compete for the privilege (i.e. horses, wolves, etc.).
Each of these elements produces more selection pressures to ensure that future generations fit into this scheme, so that the animal that doesn't share such traits becomes an outcast and is incapable of reproducing or surviving.
Altruism in Human Society
This point is brought even more sharply into focus when we consider human evolution. In human terms, an individual that is not altruistic is considered a sociopath. Psychological traits such as empathy and sympathy, should they be missing from an individual would be regarded as a defect.
What individual could ignore a child being beaten, or not defending or assisting someone that needs help? While not every occasion will necessitate a "life or death" decision, it would be an unusual individual that could act with total indifference to another person's plight. As I've mentioned elsewhere, there are enough institutions in modern society with the specific intent of providing altruistic individuals to protect the social group (military, police, fire, etc.). Holidays such as Memorial Day may as well be called "National Altruism Day" for what they represent.
What does a phrase like "defending our way of life" mean if it isn't an attempt to gain altruistic responses to defend our social group? It is no coincidence that workers perform better when they gain social recognition amongst their peers, because that brings about the desire to be more altruistic towards the company.
While some have used these ideas to promote concepts like "selfishness" as being linked to "survival of the fittest", these are seriously flawed arguments. In particular, it should be clear that there are human beings that can act with selfishness, however they can neither sustain it under all circumstances, nor can they give it enough momentum to become a significant social force to overturn the general cooperative nature of society. In other words, "selfishness" routinely fails to invade.
In short, our survival is unequivocally tied to the survival of the group. Without the group there is no individual. That's what makes it important for the group to survive, and that's what leads individuals to willingly give and even sacrifice themselves for that to happen.