All organisms constantly interact with their local environments,and they constantly change them by doing so. If,in each generation, populations of organisms modify their local environment only idiosyncratically or inconsistently, then there will be no modification of natural selection pressures and, hence, no significant evolutionary consequence. If, however, in each generation, each organism repeatedly changes its own environment in the same way, perhaps because each individual inherits the same genes causing it to do so, then the result may be a modification of natural selection. The environmental consequences of such niche construction may be transitory, and may still be restricted to single generations, but if the same environmental change is reimposed for sufficient generations, it can serve as a significant source of selection.