Ok then, give me an example of such direction. Say a feather was floating south for a minute, a gust of wind blew it north, then the wind changed and carried it south-east. What was the direction the wind was speeding it up in?
When the direction of the feather changed from south to north, it was accelerated in a northerly direction. When it then went southeast it was being accelerated southeast (feathers have a high area/mass ratio, so I'm discounting its momentum).
It seems unless you know where you want the feather to go, you can hardly talk about whether the feather was slowed down or sped up in any particular direction at any turn of the wind.
It is actually possible to determine the position, speed, and acceleration of objects without knowing where I want them to go. This is a shame, otherwise I should have a unique and lucrative job.
The word's definition is directional change. You think it's a good term for that? I don't know. Especially in the singular. When there are so many directions. Change and transformation of species might be better. Even in the title it says origins and not evolution. He used it sometimes but not overwhelmingly like it is used now.
I really don't see the problem. But if there is one, it's probably too late to change the English language now.