In those days it was thought that every visible
character in man (or in any other organism) was represented by some
"determiner" in the germ-plasm; that by suitable matings a breeder could
rid a stream of germ-plasm of almost any determiner he wished; and that
the corresponding unit character would thereupon disappear from the
visible make-up of the individual. Was a family reported as showing a
taint, for instance, hereditary insanity? Then it was asserted that by
the proper series of matings, it was possible to squeeze out of the
germ-plasm the particular concrete _something_ of which insanity was the
visible expression, and have left a family stock that was perfectly
sound and sane.
The minute, meticulous researches of experimental breeders[44] have left
such a view of heredity far behind. Certainly the last word has not been
said; yet the present hypotheses _work_, whenever the conditions are
such as to give a fair chance. The results of these studies have led to
what is called the factorial hypothesis of heredity,[45] according to
which all the visible characters of the adult are produced by (purely
hypothetical) factors in the germ-plasm; it is the factors that are
inherited, and they, under proper conditions for development, produce
the characters.
Pages:
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177