Naturalism
Naturalism, in essence, is simply the idea that human beings are completely included in the natural world: there’s nothing supernatural about us. Naturalism is based on science .... a human being comes from and is completely connected to the natural world, and is understandable in terms of those connections.
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[N]aturalism is premised on taking science as our way of knowing about the world, not tradition, intuition, sacred texts or pronouncements. By illuminating the causal connections between phenomena, science inevitably unifies what it discovers into a single, natural, multifaceted whole. If we take science seriously with regard to ourselves and our behavior, we are led to the conclusion that human beings are fully included in the natural world, and that we are completely physical creatures. More and more, biology and neuroscience show that the brain and body do everything that the soul was supposed to do. Even consciousness and our higher level capacities for rationality and choice are fully embodied, causal processes.
Some might conclude from this that naturalism reduces human beings to mere mechanisms, mere automatons, but this doesn’t follow. What follows is that the physical universe has produced, in us, marvelously complex and adaptive organisms, with the capacity for self-reflection, wonder, suffering, and joy.
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By acknowledging our origins in evolution, the naturalist perspective also enhances our feeling of kinship with the other species with which we share this planet, and our desire to sustain and nurture the planet itself. All sentient beings, including humanity, owe their existence to conditions that extend far beyond us in space and time. Seeing this, we find ourselves completely at home in the universe, full-fledged participants in the unfolding natural order.
http://www.naturalism.org/descriptions.htm#introduction