Influence of Selection 211 
tion. The fact that so many of the domesticated races breed true 
furnishes the strongest evidence in favor of the view that they 
have originated as sports and not as the result of the selection of 
fluctuating individuals. In fact, as has been said, it appears 
that a race produced by selection of fluctuations can only be 
kept up by a rigorous process of selection, as shown in the cases 
of some cultivated grains, flowers, and beets. Most domesti- 
cated races, hawever, differ from these in one all-important re- 
spect. They do not need a process of selection to maintain 
them after they have appeared, and, as I have said, this is very 
strong, indirect evidence in favor of the view that they have 
arisen by the selection of sports or discontinuous varieties, whose 
chief peculiarity is that they transmit from their inception the 
new characters to their offspring. 
LITERATURE, CHAPTER XIII 
Bumeus, H.C. The Variations and Mutations of the Introduced Sparrow. 
Biol. Lect. Woods Holl. 1897. 
The Variations and Mutations of the Introduced Littorina. Zool. 
Bull. I. 1898. 
CastEeEL, D. B., and E. F. Pairirps. Comparative Variability of Drones 
and Workers of the Honey Bee. Biol. Bull. VI. 1903. 
Crampton, H. E. On a General Theory of Adaptation and Selection. 
Jour. Exp. Zool. IT. 1905. 
Davenport, C., and BLanxinsuip, J. A Precise Criterion of Species. 
Science, VII. 1898. 
DAVENPORT C., and BuLtarp, C. Studies in Morphogenesis, VI. A 
Contribution to the Quantitative Study of Correlated Variation and 
the Comparative Variability of the Sexes. Proc. Am. Acad. Arts 
and Science, XXXII. 1896. 
Davenport, C.B. The Statistical Study of Evolution. Pop. Sci. Monthly. 
190l. 
On ce Variation of the Shell of Pecten, etc. Amer. Natural, XXXIV. 
1900. 
Gusntitative Studies in the Evolution of Pecten, III. Proc. Am. 
Acad. Arts and Science, XXXIX. 1903. 
Duncxer, G. Die Methode der Variations-Statistik. Arch. f. Entw.- 
Mech. d. Organismen, VIII. 1899. 
Fretp, W. A Contribution to the Study of Individual Variation in the 
Wings of Lepidoptera. Proc. Am. Acad. Arts and Science, 
XXXII. 1898. 
Gatton, F. Correlations and their Measurement, chiefly from Anthro- 
pometric Data. Proc. Roy. Soc. London. XLV. 1888. 
Natural Inheritance. London 1889. 
