But so far this
point has not been reached; the Americans are almost as diverse and
variable, it appears, as were their first ancestors in this country.
APPENDIX D
THE ESSENCE OF MENDELISM
It is half a century since the Austrian monk, Gregor Mendel, published
in a provincial journal the results of his now famous breeding
experiments with garden peas. They lay unnoticed until 1900, when three
other breeders whose work had led them to similar conclusions, almost
simultaneously discovered the work of Mendel and gave it to the world.
Breeding along the lines marked out by Mendel at once became the most
popular method of attack, among those who were studying heredity. It
became an extremely complicated subject, which can not be grasped
without extended study, but its fundamentals can be briefly summarized.
Inherited differences in individuals, it will be admitted, are due to
differences in their germ-plasms. It is convenient to think of these
differences in germ-plasms (that is, differences in heredity) as being
due to the presence in the germ-plasm of certain hypothetical units,
which are usually referred to as factors. The factor, nowadays, is the
ultimate unit of Mendelian research. Each of these factors is considered
to be nearly or quite constant,--that is, it undergoes little, or no
change from generation to generation.
Pages:
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670