In his celebrated essay The Hedgehog and the Fox, Isaiah Berlin draws the following distinction:
[T]here exists a great chasm between those, on one side, who relate everything to a single central vision, one system less or more coherent or articulate, in terms of which they understand, think and feel -- a single, universal, organizing principle in terms of which alone all that they are and say has significance -- and, on the other side, those who pursue many ends, often unrelated and even contradictory, connected, if at all, only in some de facto way, for some psychological or physiological cause, related by no moral or aesthetic principle; these last lead lives, perform acts, and entertain ideas that are centrifugal rather than centripetal, their thought is scattered or diffused, moving on many levels, seizing upon the essence of a vast variety of experiences and objects for what they are in themselves, without, consciously or unconsciously, seeking to fit them into, or exclude them from, any one unchanging, all-embracing, sometimes self-contradictory and incomplete, at times fanatical, unitary inner vision. The first kind of intellectual and artistic personality belongs to the hedgehogs, the second to the foxes....
There can be little doubt that Rand is a hedgehog. But what of Aristotle? Interestingly, Berlin labels him one of the foxes, and it is not hard to see why: Aristotle applied his protean genius to the entire range of knowledge at the time (founding a few sciences in the process), and he was just as comfortable in biology as in politics, in logic as in ethics, in physics as in religion, in epistemology as in aesthetics. Although Aristotle made connections between these disparate fields of investigation (a task made easier by the fact that the modern compartmentalism of knowledge was not dreamt of them), it cannot be said that he sought to impose one system or organizing principle on the phenemona he investigated.
Just as Marx was not a Marxist, Aristotle was not an Aristotelian. The systematization of Aristotle's insights came only much later, and that systematization did much violence to the questing spirit of Aristotle's researches (which John Herman Randall once aptly described as "the passionate search for passionless truth"). Those who see in Aristotle the enemy of Galileo, Copernicus, Darwin, Mendel, Newton, Einstein, and the march of modern science in general are more than missing the point. While some of Aristotle's conclusions were suspect even given the thin evidence of the day (the brain is a cooling mechanism, women are naturally inferior to men, there exists a prime mover), overall he did about the best that was possible almost two thousand years before the birth of modern science. Furthermore, there is no reason to think that Aristotle himself would have refused to look through Galileo's telescope, as modern-day Aristotelians did; on the contrary, he would have been among the first to celebrate the achievements of the modern sciences, if not in the scientific vanguard himself. Aristotle's approach to knowledge was too scientific for him to have been deeply invested in whatever system his progeny constructed out of his conclusions, because he valued science (in the broadest sense) above system.
Sadly, I don't think that we can say the same for Ayn Rand and Objectivism.