This is crying victory too soon. The difficulty of finding a method does not always prove that none can be found. But the believers in the unity of species did not admit this reserve. To set off their theory, they point to the fact that certain tribes, belonging to the same race, instead of presenting the same physical type, diverge from it very considerably. They cite the different groups of the mixed Malay-Polynesian family; and, without paying attention to the proportion of the elements which compose the mixtures, they say that if groups of the same origin can assume such totally different craniological and facial forms, the greatest diversities of that kind do not prove the primary plurality of origins.[132] Strange as it may be to European eyes, the distinct types of the negro and the Mongolian are not then demonstrative of difference of species; and the differences among the human family must be ascribed simply to certain local causes operating during a greater or less lapse of time.[133] The advocates for the plurality of races, being met with so many objections, good as well as bad, have attempted to enlarge the circle of their arguments, and, ceasing to make the skull their only study, have proceeded to the examination of the entire individual. They have rightly shown that the differences do not exist merely in the aspect of the face and formation of the skull, but, what is no less important, they exist also in the shape of the pelvis, the relative proportion of the limbs, and the nature of the pilous system. Camper and other naturalists had long since perceived that the pelvis of the negro presented certain peculiarities. Dr. Vrolik extended his researches further, and observed that in the European race the differences between the male and female pelvis are much less distinctly marked, while the pelvis of the negro, of either sex, partakes in a very striking degree of the animal character. The Amsterdam _savant_, starting from the idea that the formation of the pelvis necessarily influences that of the foetus, concludes that there must be difference of origin.[134] Mr. Weber has attacked this theory with but little success. He was obliged to allow that certain formations of the pelvis occur more frequently in one race than in another; and all he could do, was to show that the rule is not without exceptions, and that some individuals of the American, African, or Mongol race presented the forms common among the European. This is not proving a great deal, especially as it never seems to have occurred to Mr. Weber that these exceptions might be owing to a mixture of blood.