Long-term trends, also known as linear evolution or orthogenesis, are not
supported by evolutionary theory, because evolutionary theory does not
include a memory of past trends.
Response:
Orthogenesis, indeed, is not supported by evolutionary theory, which is
why it is not considered a part of modern evolutionary theory. Few if
any evolutionists today believe that evolution proceeds directly to
goals.
There are mechanisms that can cause long-term trends. For example, a
gradual climate change can cause adaptations that follow the climate
change over a long time. An evolutionary arms race can result in a
trend in the two species involved. These trends, however, are guided
by the mechanisms as they exist at the time; they are not guided by a
long-term goal.
