This is the basis of the law of "Adaptive Radiation." Prof. H. F. Osborn thus states this law:
"It is a well-known principle of zoological evolution that an isolated region, if large and sufficiently varied in its topography, soil, climate, and vegetation, will give rise to a diversified fauna according to the law of adaptive radiation from primitive and central types. Branches will spring off in all directions to take advantage of every possible opportunity of securing food. The modifications which animals undergo in this adaptive radiation are largely of mechanical nature; they are limited in number and kind by hereditary stirp or germinal influences, and thus result in the independent evolution of similar types in widely separated regions under the law of parallelism or homoplasy."
[63] This chapter and the next are in substance reprinted from an essay published by the present writer in a volume called Science Sketches. A. C. McClurg & Co., Chicago.
[72] On Fishes from Tennessee River, Alabama. American Journal of Science and Arts, xvii., 2d series, 1854, p. 26.
[73] On the Distribution of Fresh-water Fishes in the Alleghany Region of Southwestern Virginia. Journ. Acad. Nat. Sci., Phila., 1868, pp. 207-247.
[74] Introduction to the Study of Fishes, 1880, p. 211.
[75] The table below shows approximately the composition of the fresh-water fish fauna of Europe, as compared with that of North America north of the Tropic of Cancer.
Lamprey _Petromyzonidæ_ 3 species. 8 species. Paddle-fish _Polyodontidæ_ -- " 1 " Sturgeon _Acipenseridæ_ 10 " 6 " Garpike _Lepisosteidæ_ -- " 3 " Bowfin _Amiidæ_ -- " 1 " Mooneye _Hiodontidæ_ -- " 3 " Herring _Clupeidæ_ 2 " 5 " Gizzard-shad _Dorosomidæ_ -- " 1 " Salmon _Salmonidæ_ 12 " 28 " Characin _Characinidæ_ -- " 1 " Carp _Cyprinidæ_ 61 " 230 " Loach _Cobiridæ_ 3 " -- " Sucker _Catostomidæ_ -- " 51 " Catfish _Siluridæ_ 1 " 25 " Trout-perch _Percopsidæ_ -- " 2 " Blindfish _Amblyopsidæ_ -- " 6 " Killifish _Cyprinodontidæ_ 3 " 52 " Mud-minnow _Umbridæ_ 1 " 2 " Pike _Esocidæ_ 1 " 5 " Alaska blackfish _Dalliidæ_ -- " 1 " Eel _Anguillidæ_ 2 " 1 " Stickleback _Gasterosteidæ_ 3 " 7 " Silverside _Atherinidæ_ 2 " 2 " Pirate perch _Aphredoderidæ_ -- " 1 " Elassoma _Elassomidæ_ -- " 2 " Sunfish _Centrarchidæ_ -- " 37 " Perch _Percidæ_ 11 " 72 " Bass _Serranidæ_ 1 " 4 " Drum _Sciænidæ_ -- " 1 " Surf-fish _Embiotocidæ_ -- " 1 " Cichlid _Cichlidæ_ -- " 2 " Goby _Gobiidæ_ 2 " 6 " Sculpin _Cottidæ_ 2 " 21 " Blenny _Blenniidæ_ 3 " -- " Cod _Gadidæ_ 1 " 1 " Flounder _Pleuronectidæ_ 1 " -- " Sole _Soleidæ_ 1 " 1 "