Anyone ever read, Blood Music?

Through infection, conversion and assimilation of humans and other organisms the cells eventually aggregate most of the biosphere of North America into a region seven thousand kilometres wide. This civilization, which incorporates both the evolved noocytes and recently-assimilated conventional humans, is eventually forced to abandon the normal plane of existence in favor of one in which thought does not require a physical substrate. The reason for the noocytes' inability to remain in this reality is somewhat related to the strong anthropic principle.

[link to en.wikipedia.org]