The majority of evolutionists in recent years have taught that influences
exerted through the soma have no effect on the determinants in the
chromosomes of the gametes, that all hereditary variations are gametogenic
and none somatogenic. Mendelians believe that evolution has been due to
the appearance of characters or factors of the same kind as those which
distinguish varieties in cultivated organisms, and which are the subject
of their experiments, but they have found a difficulty, as already
mentioned in Chapter II, in forming any idea of the origin of a new
dominant character. A recessive character is the absence of some positive
character, and if in the cell-divisions of gametogenesis the factor for
the positive character passes wholly into one cell, the other will be
without it, will not 'carry' that factor. If such a gamete is fertilised
by a normal gamete the organism developed from the zygote will be
heterozygous, and segregation will take place in its gametes between the
chromosome carrying the factor and the other without it, so that there
will now be many gametes destitute of the factor in question. When two
such gametes unite in fertilisation the resulting organism will be a
homozygous recessive, and the corresponding character will be absent. In
this way we can conceive the origin of albino individuals from a coloured
race, supposing the colour was due to a single factor.

In Bateson's opinion the origin of a new dominant is a much more difficult
problem. In 1913 he discussed the question in his Silliman Lectures.
[Footnote: _Problems of Genetics_, Oxford Univ. Press, 1913.] He considers
the difficulty is equally hopeless whether we imagine the dominants to be
due to some change internal to the organism or to the assumption of
something from without. Accounts of the origin of new dominants under
observation in plants usually prove to be open to the suspicion that the
plant was introduced by some accident, or that it arose from a previous