Evolution "for the Good of the Group"

Is evolution a team sport, or is the contest f r survival played out strictly between individuals? There's no question that natural selection acts on individual organisms: Those with favorable traits are more likely to pass along their genes to the next genera tion. But perhaps similar processes could operate at other levels of the bio logical hierarchy. In this way natural selection could perpetuate traits that are favorable not to an individual but to a social unit such as a flock or a col ony, or to an entire species, or even to an ecosystem made up of many spe cies. The underlying question is: Can biological traits evolve for the good of the group? Many early biologists accepted the idea of group selection without think ing very critically about it. For exam ple, herds of grazing animals might be described as evolving to conserve their food supply over the long term. Herds