There is a certain perfect ideal form that every plant or animal somehow resembles, but even having achieved perfection, the organism will improve upon this, which is to say that the tendency is to continue evolving to be even better than perfection.
This shifts the goal from perfection to Amelioration, ie. we aren't really trying to become perfect, rather we're trying to get better and better and better (Ameliorate).
Amelioration doesn't only happen after perfection, there are two different things going on: not only is the organism trying to attain some "perfect form", it's also trying to improve on the blueprints while adapting to physical conditions.
Some seeds are planted under more favorable conditions than others and so they get further.
Strive towards perfection. And not only strive for perfection, but even having achieved perfection, always go a bit further.