In the opinion of many scientific observers, who judge from the first impression, and take extremes[118] as the basis of their reasoning, the groups of the human family are distinguished by differences so radical and essential, that it is impossible to believe them all derived from the same stock. They, therefore, suppose several other genealogies besides that of Adam and Eve. According to this doctrine, instead of but one species in the genus _homo_, there would be three, four, or even more, entirely distinct ones, whose commingling would produce what the naturalists call _hybrids_. General conviction is easily secured in favor of this theory, by placing before the eyes of the observer instances of obvious and striking dissimilarities among the various groups. The critic who has before him a human subject with a skin of olive-yellow; black, straight, and thin hair; little, if any beard, eyebrows, and eyelashes; a broad and flattened face, with features not very distinct; the space between the eyes broad and flat; the orbits large and open; the nose flattened; the cheeks high and prominent; the opening of the eyelids narrow, linear, and oblique, the inner angle the lowest; the ears and lips large; the forehead low and slanting, allowing a considerable portion of the face to be seen when viewed from above; the head of somewhat a pyramidal form; the limbs clumsy; the stature humble; the whole conformation betraying a marked tendency to obesity:[119] the critic who examines this specimen of humanity, at once recognizes a well characterized and clearly defined type, the principal features of which will readily be imprinted in his memory. Let us suppose him now to examine another individual: a negro, from the western coast of Africa. This specimen is of large size, and vigorous appearance. The color is a jetty black, the hair crisp, generally called _woolly_; the eyes are prominent, and the orbits large; the nose thick, flat, and confounded with the prominent cheeks; the lips very thick and everted; the jaws projecting, and the chin receding; the skull assuming the form called prognathous. The low forehead and muzzle-like elongation of the jaws, give to the whole being an almost animal appearance, which is heightened by the large and powerful lower-jaw, the ample provision for muscular insertions, the greater size of cavities destined for the reception of the organs of smell and sight, the length of the forearm compared with the arm, the narrow and tapering fingers, etc. "In the negro, the bones of the leg are bent outwards; the tibia and fibula are more convex in front than in the European; the calves of the legs are very high, so as to encroach upon the hams; the feet and hand, but particularly the former, are flat; the os calcis, instead of being arched, is continued nearly in a straight line with the other bones of the foot, which is remarkably broad."[120]