Prichard, a Bristol physician, classified and systematized facts relating to the races of men better than any previous writer. His interest in anthropology was stimulated by one of the pressing questions of his day: Did all the races of mankind have a common origin, as stated in the Scriptures, or did they spring from different ancestral stocks? Prichard, a confirmed monogenist, sought to demonstrate the common origin of the human races by compiling evidence from a variety of fields, including anatomy, physiology, comparative psychology, linguistics and cross-cultural studies. He theorized that the earliest races of mankind had been dark-skinned, and that the black races, far from representing a degeneration from white "perfection," were the origin from which the white races had sprung.

The second edition of his book, 1826, contains a remarkable anticipation of modern views on evolution, views which were suppressed in later editions. Facsimile edited with an introductory essay [and bibliography] by G. W. Stocking, Jr., Chicago, University Press, 1973. The one-volume first edition was unillustrated. By the 3rd edition the work was expanded to 5 vols. (1836-47) and contained many color plates. In that form it synthesized all then known information about the various races of mankind, forming a basis for modern ethnological research.

Prichard issued a popularization of his work, with numerous color plates, as The natural history of man (1843). The fourth edition of that was edited and enlarged, and published in 2 vols. by Edwin Norris (1855).