The basic idea’s petty straightforward. Natural selection reaches into every corner of the biosphere, you see; and a billion years ago that meant every cell for itself because unicellular life was the only game in town. A mere six hundred million years back, though, all that had changed. Metazoans were everywhere — cells grouped into colonies with specialized subsystems called tissues and organs —and somehow, within those colonies, the whole beat-the-competition thing had fallen out of favor. Cells worked together, now; hell, red blood cells even gave up their nuclei for the good of the organism, which really puts the kibosh on any future solo career. I think it had something to do with inclusive fitness.
In between, presumably, there was something halfway between Cuba and the US, some intermediate form between everyone for themselves and everyone for the state. Some kind of loose affiliation of cells which valued their individual freedom, but were not above at least some level of cooperation. Modern-day sponges might be a pretty good example: some cellular specialization, a bit of the ol’ helping hand between cells, but nothing so altruistic as an actual tissue. Call it “Metazoa 1.0″.
Peter Watts has a gift for digging up truly creepy science.