I believe in Chaos theory. Evolution of the species is like the vessels of a river, they always follow the road of the least resistance, that consumps the least energy.
If a mutation is favorable, it leads in the "right" direction, the species will develop further in that direction.
If a mutation is not favorable , it leads in the wrong direction which will become almost immediately a dead and for further development.
So actually the ball rolls downhill.
Yup, it appears to going uphill when in fact it is following the path of least resistance