The current conception concerning the origin of species assumes that
species are slowly converted into others. The conversion is assumed to
affect all the individuals in the same direction and in the same degree.
The whole group changes its character, acquiring new attributes. By
inter-crossing they maintain a common line of progress, one individual
never being able to proceed much ahead of the others.
The birth of the new species necessarily seemed to involve the death of
the old one. This last conclusion, however, is hard to understand. It
may be justifiable to assume that all the individuals of one locality
are ordinarily intercrossed, and are moreover subjected to the same
external conditions. They might be supposed to vary in the same
direction if these conditions were changed slowly. But this could of
course have no possible influence on the plants of the [561] same
species growing in distant localities, and it would be improbable they
should be affected in the same way. Hence we should conclude that when a
species is converted into a new type in one locality this is only to be
considered as one of numerous possible ones, and its alteration would
not in the least change the aspect of the remainder of the species.
But even with this restriction the general belief is not supported by
the evidence of the evening-primroses. There is neither a slow nor a
sudden change of all the individuals. On the contrary, the vast majority
remain unchanged; thousands are seen exactly repeating the original
prototype yearly, both in the native field and in my garden. There is no
danger that _lamarckiana_ might die out from the act of mutating, nor
that the mutating strain itself would be exposed to ultimate destruction
from this cause.
In older swarms, such as _Draba_ or _Helianthemum_, no such center,
around which the various forms are grouped, is known. Are we to conclude
therefore that the main strain has died out? Or is it perhaps concealed
among the throng, being distinguished by no peculiar character? If our
_gigas_ and _rubrinervis_ were growing in equal numbers with the
_lamarckiana_ in the native field, would it be possible to decide [562]
which of them was the progenitor of the others? Of course this could be
done by long and tedious crossing experiments, showing atavism in the
progeny, and thereby indicating the common ancestor. But even this
capacity seems to be doubtful and connected only with the state of
mutability and to be lost afterwards. Therefore if this period of
mutation were ended, probably there would be no way to decide concerning
the mutual relationship of the single species.
Hence the lack of a recognizable main stem in swarms of elementary
species makes it impossible to answer the question concerning their
common origin.
Another phase of the opposition between the prevailing view and my own
results seems far more important. According to the current belief the
conversion of a group of plants growing in any locality and flowering
simultaneously would be restricted to one type. In my own experiments
several new species arose from the parental form at once, giving a wide
range of new forms at the same time and under the same conditions.