- Although humans currently comprise only about one-half of one percent of the total living biomass on Earth, the human effect on nature is disproportionately large.
- Because of the extent of human influence, the boundaries between what we regard as nature and "made environments" is not clear cut except at the extremes. Even at the extremes, the amount of natural environment that is free of discernible human influence is presently diminishing at an increasingly rapid pace.
- The conservation of biological diversity has become a global concern. Although not everybody agrees on extent and significance of current extinction, most consider biodiversity essential.