The "Level of Selection" debate in evolutionary theory has been going on for decades, with the advocates of lower levels (e.g., the Selfish Gene) usually drubbing, through better math, the advocates of significant amounts of selection at the group level.
Personally, I've always found the arguments for group selection plausible (although that probably just shows how bad at math I am). Think of two tribes in prehistoric northern Europe squaring off militarily along the river that divides their traditional territories. They each covet the others' lands, but both groups have been afraid to attempt a river crossing under archery fire. One tribe is mostly lactose tolerant, the other tribe is mostly not. The leaders of the lactose tolerant tribe decide to send their cavalry, without their grain wagons, on a multiday sweep up the river in an attempt to turn the enemies' flank. They can drink mare's milk on their expedition. The lactose intolerant tribe's cavalry attempts to follow them, but gets slowed down by their food wagons. The milk-drinking cavalry outdistances the non-milk drinking cavalry to the point where they can get a full day free to cross the river.
In the next generation, the women of the lactose intolerant former tribe have many children who are lactose tolerant. The men don't have many children at all.
Now, that seems to me like group selection with a bang. Membership in the group -- outflankers or outflankees -- determines much about the fate of your genes in future generations.
But, it's often been explained to me that that's not real group selection, which can't happen because cheaters would undermine the evolution of altruism.
Okay, but, I've long had the hunch that this debate isn't framed as productively as it could be.
In recent years, Edward O. Wilson, the ant expert and author of Sociobiology, has taken up the the cudgels for the concept of group selection, which has widely been seen as evidence of imminent senility. A commenter, however, offers an interesting perspective.
Many here have missed the terms of this controversy. EO Wilson & co's change of mind was forced by 1999 work by James Hunt who studied multiple origins of sociality in a wasp phylogeny in which all the species had about the same “kin selection potential” and found that sociality evolved when there were strong “ecological” incentives (Hunt JH 1999. Trait mapping and salience in the evolution of eusocial vespid wasps. Evolution 53: 225-237). But since ~2005 Wilson, Hoelldobler, etc, have hijacked the controversy.
People have indeed started realizing that crucial for the existence/persistence –and thus for the evolution– of animal societies is not (or not so much) “kin selection” but rather the very rewarding ecological niches out there in which biomachines that adopt group-approaches to foraging and interference competition are much more effective trophically than are biomachines which adopt “solitary-consumer/fighter/reproducer” strategies.
This means that the evolutionary success of the genetic programs encoding such group behaviors is fully subordinate to the existence of such ecological opportunities!
In other words: people have begun realizing that, e.g., “altruism” is also a winning ecological strategy, rather than just an example of the promotion, or not, of altruism genes and the rejection (or invasion) of cheater genes.
The social-ant colony, e.g., is an ecological machine that out-competes at the foraging- and interference-competition level most other organisms in almost any terrestrial ecological setting, i.e., a social-ant colony in the field cannot be reduced natural-historically and evolutionary-historically to just an example of an Evolutionarily Stable Strategy immune to “selfishness” mutations that may undermine the genetic encoding of its sociality.
Wilson indeed has always made a big deal of the fact that ant species monopolize nearly 70% of the insect biomass on earth, but he did not realize the implications of this until the wasp guy rubbed it in to him and his coterie while they were still happily repeating the empty syllogisms of kin-selection numerologists [who meanwhile have even almost managed to deny Darwin (sic!) the credit for explaining the existence of sterile ants, etc., when he mentioned in the Origin of Species that an individual's sacrifice can benefit the reproduction of relatives, i.e., kin selection].
This 70% means that evolution by “natural selection of individuals” delivers niche-occupancy strategies that suffice to claim only ~30 of the trophic energy monopolized by the insect Bauplan (assuming termites and other social insects are insignificant biomass-wise).
The situation among many mammals is the same. Wild-dog packs and hyenas, e.g., beat the hell out of tigers and lions, and biomass wise they dominate.
It is time for gratuitous faux-aprioristic arguments to be confronted with ultimate natural-historical facts. And it is also time that the applied-math peddlers posturing as evolutionary biologists learn that “natural selection” is not the same as “evolution by natural selection”, that differential fitness is always caused by differential ecological performance (and never by “genes”), and that evolution by natural selection is just something that “may” happen when there is differential ecological performance at some level of biological organization, which however does not “prove” that ecological performance is caused by molecular interactions of genes (or of proteins; genes may suffice but are not necessary for differential performance, but additive genetic variation in performance suffices for evolution driven by differential ecological performance).
In other words, Sober’s 1984 [1984 sic!] book “The Nature of Selection” should be required reading for every evolutionary biologist. Sober showed first that the “kin selection” oxymoron is a muddled verbal construct to refer to that special case of group-level differential ecological performance in which “selected” groups happen to also be kin groups (most of the time but not always... see mutualism, e.g.).