THE purpose of these lectures is to point out the means and methods by
which the origin of species and varieties may become an object for
experimental inquiry, in the interest of agricultural and horticultural
practice as well as in that of general biologic science. Comparative
studies have contributed all the evidence hitherto adduced for the
support of the Darwinian theory of descent and given us some general
ideas about the main lines of the pedigree of the vegetable kingdom, but
the way in which one species originates from another has not been
adequately explained. The current belief assumes that species are slowly
changed into new types. In contradiction to this conception the theory
of mutation assumes that new species and varieties are produced from
existing forms by sudden leaps. The parent-type itself remains unchanged
throughout this process, and may repeatedly give birth to new forms.
These may arise simultaneously and in groups or separately at more or
less widely distant periods.
The principal features of the theory of mutation have been dealt with at
length in my book "Die Mutationstheorie" (Vol. I., 1901, Vol. II., 1903.
Leipsic, Veit & Co.), in which I have endeavored to present as
completely as possible the detailed evidence obtained from trustworthy
historical records, and from my own experimental researches, upon which
the theory is based.
The University of California invited me to deliver a series of lectures
on this subject, at Berkeley, during the [vii] summer of 1904, and these
lectures are offered in this form to a public now thoroughly interested
in the progress of modern ideas on evolution. Some of my experiments and
pedigree-cultures are described here in a manner similar to that used in
the "Mutationstheorie," but partly abridged and partly elaborated, in
order to give a clear conception of their extent and scope. New
experiments and observations have been added, and a wider choice of the
material afforded by the more recent current literature has been made in
the interest of a clear representation of the leading ideas, leaving the
exact and detailed proofs thereof to the students of the larger book.
Scientific demonstration is often long and encumbered with difficult
points of minor importance. In these lectures I have tried to devote
attention to the more important phases of the subject and have avoided
the details of lesser interest to the general reader.
Considerable care has been bestowed upon the indication of the lacunae
in our knowledge of the subject and the methods by which they may be
filled. Many interesting observations bearing upon the little known
parts of the subject may be made with limited facilities, either in the
garden or upon the wild flora. Accuracy and perseverance, and a warm
love for Nature's children are here the chief requirements in such
investigations.
In his admirable treatise on Evolution and Adaptation (New York,
Macmillan & Co., 1903), Thomas Hunt Morgan has dealt in a critical
manner with many of the speculations upon problems subsidiary to the
theory of descent, in so convincing and complete a manner, that I think
myself justified in neglecting these questions here. His book gives an
accurate survey of them all, and is easily understood by the general
reader.
In concluding I have to offer my thanks to Dr. D.T. MacDougal and Miss
A.M. Vail of the New York Botanical Garden for their painstaking work in
the preparation of the manuscript for the press. Dr. MacDougal, by
[viii] his publications, has introduced my results to his American
colleagues, and moreover by his cultures of the mutative species of the
great evening-primrose has contributed additional proof of the validity
of my views, which will go far to obviate the difficulties, which are
still in the way of a more universal acceptation of the theory of
mutation. My work claims to be in full accord with the principles laid
down by Darwin, and to give a thorough and sharp analysis of some of the
ideas of variability, inheritance, selection, and mutation, which were
necessarily vague at his time. It is only just to state, that Darwin
established so broad a basis for scientific research upon these
subjects, that after half a century many problems of major interest
remain to be taken up. The work now demanding our attention is
manifestly that of the experimental observation and control of the
origin of species. The principal object of these lectures is to secure a
more general appreciation of this kind of work.
HUGO DE VRIES.
Amsterdam, October, 1904.
[ix]