Just as Brutus was a close companion to Caesar but proved to be his undoing, evolutionary theory seemed to provide a rock-solid foundation for individualism--until Lynn Margulis came along.
Lynn is famous so you might already know her story. In the 1970's she proposed the radical theory that nucleated (eukaryotic) cells evolved not by small mutational steps from bacterial (prokaryotic) cells, but as symbiotic communities of bacteria that became so integrated that the group became a higher-level organism. She was fiercely opposed but carried the day, an accomplishment so great that she was admitted into the National Academy of Sciences in 1983.
The concept of the organism as a group was generalized in the 1990s by John Maynard Smith and Eors Szathmary in two books titled The Major Transitions of Evolution and The Origins of Life: From the Birth of Life to the Origins of Language. Their theory was multilevel selection theory with a twist. The evolution of group-level adaptations requires a process of group-level selection and is undermined by selection within groups. Now for the twist: The balance between levels of selection is not static but can itself evolve. When between-group selection sufficiently dominates within-group selection, the group becomes a superorganism and the lower-level organisms acquire the status of organs. The evolution of nucleated cells was just one of many major transitions, preceded by the evolution of the first cells and possibly even the origin of life itself as groups of cooperating molecular interactions, and followed by the evolution of multicellular organisms, social insect colonies, and--as we shall see--human social groups.
John Maynard Smith is the same person who opposed group selection in the 1960s, as I recount in T&R VII and IX. Somehow he managed to make group selection the lynch pin of major transitions without ever acknowledging an error in his earlier views. Eors Szathmary, his coauthor, fully appreciates the continuity of ideas. Joel Peck is another theoretical biologist who is fully comfortable with multilevel selection and was close to John during the last years of his life. I recently asked Joel how John could have been so schizophrenic about his early and later ideas. Joel shrugged and replied with a question of his own: How does anyone believe in ideas that are inconsistent with each other, such as scientists who also accept religious dogma? Perhaps Maynard Smith simply couldn't bring himself to thoroughly reconsider his earlier ideas on the basis of his own later ideas.
It might seem that the evolution of multi-cellular organisms from single-celled organisms would be simple when they begin as a single cell because all the cells are genetically identical and there can be no selection within groups. Wrong. Mutations occur with every cell division and there are thousands of cell divisions in the lifetime of a multi-cellular organism such as you and I. Mutant cells that are selectively advantageous within the organism are certain to arise and spread, regardless of their effect on the welfare of the group. Cancer is just multilevel selection in which we are the groups. Over the eons, elaborate physiological mechanisms have evolved by between-individual selection to suppress within-individual selection as much as possible.
The concept of major transitions is one of the most important developments in modern evolutionary thought, but the implications for individualism and multilevel selection theory are seldom discussed. Individualism is the claim that individual organisms are a privileged level of the biological hierarchy, that all of nature and human nature can be explained in terms of individual-self interest, that groups can emphatically not be regarded as organisms writ large, that the idea of individuals evolving "for the good of the group" is deeply erroneous. If within-group selection invariably trumps between-group selection, then all of these claims would be true and evolution would indeed provide a rock-solid foundation for individualism. That's why the issues at stake in the 1960s seemed, and were, momentous.
The issues remain momentous when we decide that between-group selection is important after all and can even dominate within-group selection in the case of major transitions. If we noted the rock-solid foundation that evolutionary theory seemed to provide individualism before, we should equally note when the foundation crumbles. Individualism has nothing left to stand on. Individual organisms are highly integrated and tightly regulated societies. Organisms turn into mere groups when their organization is disrupted by natural selection from within. Mere groups turn into organisms when between-group selection trumps within-group selection. When selection operates at both levels, individuals become strange hybrids of solid citizens and self-seekers, while groups become strange hybrids of coordinated units and dysfunctional outcomes of conflict from within.
Some people will mourn and others will celebrate the death of individualism, but everyone needs to bury it and move on to explore the implications of multilevel selection theory, especially in the realm of human affairs.