 McShea observes that the most popular hypothesis, among scientists, is that there is a largest-scale trend towards increasing complexity.Evolutionary theorists agree that there are local trends in evolution, such as increasing brain size in hominids, but these directional changes do not persist indefinitely, and trends in opposite directions also occur (Gould, 1997).Evolution causes organisms to adapt to their local environment; when the environment changes, the direction of the trend may change.