geology are different in nature from history and literary criticism.
One obvious difference is that astronomy and geology deal with the non-human natural world, while history and literary criticism deal with human events and the human mind. This certainly draws a fairly sharp line between the subject matter that we associate with the sciences and that of disciplines we do not regard as sciences. It even explains the ambiguity of the "social sciences;" in spite of its name, political science is liable to strike us as an art rather than a true science.
Yet some of the sciences certainly deal with human beings. The theory of evolution, the central theory of modern biology, incorporates humans along with other animals, and while human evolution may be rejected for religious reasons, there is no reason to suppose that biologists feel themselves on any less firm ground there than in any other part of their field. And if we accept the biologists, human beings are themselves part of nature. Why should "science" tend for the most part to shy away from human affairs, abandoning them to the social sciences and the humanities?
Perhaps to get a stronger sense of what science is (and isn't), we should turn to how science operates. One widely accepted view of the characteristics of sciences is that offered by Thomas S. Kuhn in The Structure of Scientific Revo
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