Humans are no more evolved than any other creature. Evolution is a process, it has no "goal" other then it's an expression we smart apes use to describe semi-random chemical connections that "work" better in their environment than others. Sometimes the "evolutionary" changes are a "positive", yet even our intelligence comes at a huge metabolic cost in comparison to the bulk of lifeforms (ie enough electricity to light a light bulb). When the planetary environment changes rapidly, even on a local scale from volcanoes, certain members of species inside the extinction area might have some quirk that makes it run a bit faster to escape so it reproduces. That's it, there is no "upward" driving force in evolution.
Gravity has no goal either, but its effects have a definite direction. Evolution has a starting point: very simple life forms. That means that at any particular level of complexity, the less complex ecological niches are already full, while the more complex are vacant. And as the more complex niches are filled, they open up yet more complex ones "above" them. The end result is that while individual species may evolve in various ways, evolution as a whole has a definite direction.
Furthermore, complexity seems to increase in identifiable leaps. For example, humans have all the mental faculties that, say, crocodiles do - the so-called "reptile brain" - and some extra on top of that. So it would be perfectly valid to say that humans are more evolved than crocodiles, just as it would be valid to say crocodiles are more evolved than amoebas, and amoebas more evolved than bacteria.
So yes, there's an upward driving force in evolution. It arises due to self-interaction: evolution is both guided by and affects the environment.