From the discoveries that he made during his five-year voyage aboard HMS Beagle, furthered by another 20 years of study and research, Charles Darwin produced this scientific masterpiece in 1859. On the Origin of Species was a revolutionary yet surprisingly readable treatise of natural philosophy (as science was still often referred to at the time), in which Darwin articulated his theory of natural selection—or "survival of the fittest"—to explain the appearance of new species, placing himself at the center of a fiery debate on evolution that still smolders today.