Nature's selection of viable strengths through environmental pressures that force an organism to adapt. The bat that hears better than the rest stands a better chance of living long enough to pass on that kind of hearing. In this way certain favorable genes--favorable to adapting to environment pressures--gradually become more numerous in a given population. Discovered by Charles Darwin and Alfred Russel Wallace in 1858 (rather, discovered years earlier by both; Darwin beat Wallace to the press in 1858). Whether the environment shapes completely passive life-material or interacts with an emerging and ever-more-conscious creative potentiality is a most interesting current debate. See Evolution.