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Comparison with 1859
and English pointer have apparently both gone on slowly diverging in character from their original stocks, without either having given off any fresh branches or races.
After ten thousand generations, species (A) is supposed to have produced three forms, a 10 , f 10 , and m 10 , which, from having diverged in character during the successive generations, will have come to differ largely, but perhaps unequally, from each other and from their common parent. If we suppose the amount of change between each horizontal line in our diagram to be excessively small, these three forms may still be only well-marked varieties; or they may have arrived at the doubtful category of sub-species; but we have only to suppose the steps in the process of modification to be more numerous or greater in amount, to convert these three forms into well-defined species: thus the diagram illustrates the steps by which the small differences distinguishing varieties are increased into the larger differences distinguishing species. By continuing the same process for a greater number of generations (as shown in the diagram in a condensed and simplified manner), we get eight species, marked by the letters between a 14 and m 14 , all descended from (A). Thus, as I believe, species are multiplied and genera are formed.
In a large genus it is probable that more than one species would vary. In the diagram I have assumed that a second species (I) has produced, by analogous steps, after ten thousand generations, either two well-marked varieties ( w 10 and z 10 ) or two species, according to the amount of change supposed to be represented be- tween the horizontal lines. After fourteen thousand generations, six new species, marked by the letters n 14 to z 14 , are supposed to have been produced. In each genus, the species, which are already extremely different in
and English pointer have apparently both gone on slowly diverging in character from their original stocks, without either having given off any fresh branches or races.
After ten thousand generations, species (A) is supposed to have produced three forms, a 10 , f 10 , and m 10 , which, from having diverged in character during the successive generations, will have come to differ largely, but perhaps unequally, from each other and from their common parent. If we suppose the amount of change between each horizontal line in our diagram to be excessively small, these three forms may still be only well-marked varieties; or they may have arrived at the doubtful category of sub-species; but we have only to suppose the steps in the process of modification to be more numerous or greater in amount, to convert these three forms into well-defined species: thus the diagram illustrates the steps by which the small differences distinguishing varieties are increased into the larger differences distinguishing species. By continuing the same process for a greater number of generations (as shown in the diagram in a condensed and simplified manner), we get eight species, marked by the letters between a 14 and m 14 , all descended from (A). Thus, as I believe, species are multiplied and genera are formed.
In a large genus it is probable that more than one species would vary. In the diagram I have assumed that a second species (I) has produced, by analogous steps, after ten thousand generations, either two well-marked varieties ( w 10 and z 10 ) or two species, according to the amount of change supposed to be represented .. between the horizontal lines. After fourteen thousand generations, six new species, marked by the letters n 14 to z 14 , are supposed to have been produced. The species of a genus which are already extremely different in