Heredity and sex . Johannsen.) the tops of the beans, the line gives a curve like thatshown in Fig. 62. This is known as the curve of prob-ability. The curve can be, of course, most readilymade by making the measurements directly. Mostindividuals of such a population will have the charac-ter developed to the degree represented by the highestpoint in the curve. Now if two individuals standingat one side (let us say with the character in questionbetter developed than the average) become the parent 124 HEREDITY AND SEX of the next generation, their offspring will make a newcurve that has moved, s
Heredity and sex . Johannsen.) the tops of the beans, the line gives a curve like thatshown in Fig. 62. This is known as the curve of prob-ability. The curve can be, of course, most readilymade by making the measurements directly. Mostindividuals of such a population will have the charac-ter developed to the degree represented by the highestpoint in the curve. Now if two individuals standingat one side (let us say with the character in questionbetter developed than the average) become the parent 124 HEREDITY AND SEX of the next generation, their offspring will make a newcurve that has moved, so to speak, in the direction ofselection (Fig. 63). If again two more extreme individuals are selected,another step is taken. The process is assumed to goon as long as the selection process is maintained. So the matter stood until a Danish botanist, Johann-sen, set seriously to work to test the validity of theassumption, using a race of garden beans for his meas-urements. He discovered in the first place that popu-. FiG. 63. — Schematic representation of the type-shifting effect of selec-tion from the point of view of Galtons reversion theory. The * marks thepoint on the curves oi A, Ai, A2 from which the selection is supposed to bemade. (Goldschmidt.) lations are made up of a number of races or ^purelines. When we select in such a population we sortout and separate its constituent races, and sooneror later under favorable conditions can get a purerace. Selection has created nothing new; it haspicked out a particular preexisting race from a mixedpopulation. Johannsen has shown that within a pure line selec-tion produces no effect, since the offspring form thesame group with the same mode as the group from whichthe parents came. The variability within the purelines is generally ascribed to environmental influences SECONDARY SEXUAL CHARACTERS 125 which are recurrent in each generation. The germ-plasm is homogeneous for all members of the pure line,while in a mixed population th
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Keywords: ., boo, bookcentury1900, bookdecade1910, booksubjectsex, bookyear1913
