The noosphere concept was originally proposed as a sphere of mind or thought that has emerged from the biosphere over the course of human evolution. Two versions of the noosphere concept were developed in the 20th century and they differed with respect to whether the noosphere was to be considered separate from the biosphere or a new form of the biosphere. Both versions shared an assumption that collective human thought based on a scientific epistemology would achieve a benevolent relationship with the biosphere. Research in global ecology continues to reveal the growing influence of humanity on the biota and on the global biogeochemical cycles, but recent history has not confirmed humanity's ability to self-regulate. Nevertheless, the noosphere concept remains useful because it acknowledges the uniquely subjective aspect of human brain functioning and the propensity for humans to share ideas and work collaboratively. Both of these features will be needed to develop a structured coupling of humanity and the biosphere that preserves the biophysical processes sustaining the ecosphere.