Paraphyly

[Richard Jensen]

Joseph Laferriere writes
>...
> The only time directional selection will be in effect is either
> during periods of climatic change or if the species is invading a new
> habitat.
This is an oversimplification of the forces of selection - directional
selection could also occur as a result of response to herbivore pressure,
invasion of new competitors (i.e., weeds), response to fungal or other
parasites, etc.  In other words, there are many phenomena, in addition to
climatic change or invading new habitats, that could lead to directional
selection.

Dick Jensen