Quotes from this video which are most pertinent to stuff I've talked about before:
"You'll have little cells competing, then at some point, some of them decide to group together and cooperate & become specialized - and you get multicellular creatures. You see a similar pattern when individuals group together, forming very simple societies and out-competing the individuals."
"I see evolution as...this interplay of competition driving cooperation, driving specialization which then brings the competition to the next level."
In other words, competitive pressure drives organizational structures towards ever-greater complexity as previously unrelated entities are forced to either stand together or fall apart.
This is very similar to what Nonzero calls the "logic of human destiny": the reason why sentient life, societies, and world wars were inevitable from the time the first single-celled organisms appeared. I think Robert Wright (author of Nonzero, no relation to Will Wright that I know of) also refers to this as the "arms race" of cooperation: stubborn individualists are eventually dominated by coalitions of their enemies, whether we're talking about cells, species, or societies.