1. Quills yellow. 1. Quills red.
2. Male with black cheek stripe. 2. Male with red cheek stripe.
3. Adult female with no 3. Adult female with usually
cheek stripe. brown cheek stripe.
4. A scarlet nuchal crescent 4. No nuchal crescent in
in both sexes. either sex.
5. Throat and fore-neck brown. 5. Throat and fore-neck grey.
6. Top of head and hind-neck grey. 6. Top of head and hind-neck brown.
7. General tone of plumage 7. General tone of plumage olivaceous. rufescent.
C. auratus occurs all over Canada, and the United States, from the north to Galveston; westwards it extends to Alaska and the Pacific coast to the northern border of British Columbia. C. cafer in comparatively pure form occupies Mexico, Arizona, California, part of Nevada, Utah, Oregon, and is bounded on the east by a line drawn from the Pacific south of Washington State, south and eastward through Colorado to the mouth of the Rio Grande on the Gulf of Mexico. Between the two areas thus roughly defined is a tract of country about 300 to 400 miles wide, which contains some normal birds of each type, but chiefly birds exhibiting irregular mixtures of the characters of both. Bateson remarks that some naturalists may be disposed once more to appeal to our ignorance, and suggest that if we only knew more we should find that the yellow quills, the black 'moustache,' and the red nuchal crescent specially adapt auratus to the conditions of the northern and eastern region, while the red quills, red moustache, and absence of crescent fit cafer to the conditions of the more southern and western territory. But, as the author we are quoting points out, when we think of the wide range of conditions in the country occupied by auratus, extending from Florida to the Arctic, it is impossible to believe that there is any common element in the conditions which demands a scarlet nuchal patch in auratus, while the equally varied conditions in the cafer area do not require that character. It may be added that the same objection is equally valid whether we apply it to the utility of such a character or to the supposition that the character has been caused by external conditions; in other words, whether we attempt to explain the facts by selection or by the Lamarckian principle.
Another case quoted by Bateson is that of the two common British Wasps, Vespa vulgaris and Vespa germanica. Both usually make subterranean nests, but of somewhat different materials. That of V. vulgaris is of a characteristic yellow colour, because made of rotten wood, while that of V. germanica is grey, from the weathered surface wood of palings or other exposed timber which is used in its construction. In characters the differences of the two forms are so slight as to be distinguishable only by the expert. V. vulgaris often has black spots on the tibiae, which are wanting in germanica. A horizontal yellow stripe on the thorax is enlarged downwards in the middle in germanica, not in vulgaris. There are distinct though slight differences in the genital appendages of the males in the two species. Here there are differences of habit, and slight but constant differences of structure; but it is impossible to find any relation between the former and the latter.
Mendelism in itself affords no evidence of the origin of new characters, since it deals only with the heredity of the characters which it finds usually in the varieties of cultivated animals and plants. But indirectly it draws the inference that new characters arose in the form in which they are found to be inherited, as complete units, and not by gradual, continuous increase, that specific characters are due to mutations, and that all evolution has been the result of similar hereditary factors, arising by some internal process in the divisions of reproductive cells, and not determined by external conditions. Some Mendelians maintain that if the mutations are not compatible with the existing conditions of life, the organism must either die or find new conditions in which it can live.