



Produced by Chris Curnow, Paul Marshall and the Online
Distributed Proofreading Team at http://www.pgdp.net (This
file was produced from images generously made available
by The Internet Archive)






                    YALE UNIVERSITY

        MRS. HEPSA ELY SILLIMAN MEMORIAL LECTURES


                  PROBLEMS OF GENETICS

              SILLIMAN MEMORIAL LECTURES
          PUBLISHED BY YALE UNIVERSITY PRESS

  ELECTRICITY AND MATTER. _By_ JOSEPH JOHN THOMSON,
    D.SC., LL.D., PH.D., F.R.S., _Fellow of Trinity College,
    Cambridge, Cavendish Professor of Experimental Physics, Cambridge_.
  _Price $1.25 net; postage 10 cents extra._

  THE INTEGRATIVE ACTION OF THE NERVOUS SYSTEM.
    _By_ CHARLES S. SHERRINGTON,
     D.SC., M.D., HON. LL.D., TOR., F.R.S.,
    _Holt Professor of Physiology in the University of Liverpool_.
  _Price $3.50 net; postage 25 cents extra._

  RADIOACTIVE TRANSFORMATIONS. _By_ ERNEST RUTHERFORD,
    D.SC., LL.D., F.R.S., _Macdonald Professor of Physics,
    McGill University_.
  _Price $3.50 net; postage 22 cents extra._

  EXPERIMENTAL AND THEORETICAL APPLICATIONS OF
      THERMODYNAMICS TO CHEMISTRY.
  _By_ DR. WALTHER NERNST, _Professor and Director of the
    Institute of Physical Chemistry in the University of Berlin_.
  _Price $1.25 net; postage 10 cents extra._

  THE PROBLEMS OF GENETICS. _By_ WILLIAM BATESON, M.A.,
    F.R.S., _Director of the John Innes Horticultural Institution,
    Merton Park, Surrey, England_.
  _Price $4.00 net; postage 25 cents extra._

  STELLAR MOTIONS.
    WITH SPECIAL REFERENCE TO MOTIONS DETERMINED BY MEANS OF
    THE SPECTROGRAPH. _By_ WILLIAM WALLACE CAMPBELL, SC.D., LL.D.,
   _Director of the Lick Observatory, University of California_.
  _Price $4.00 net; postage 30 cents extra._

  THEORIES OF SOLUTIONS. _By_ SVANTE AUGUST ARRHENIUS,
    PH.D., SC.D., M.D., _Director of the Physico-Chemical
    Department of the Nobel Institute, Stockholm, Sweden_.
  _Price $2.25 net; postage 15 cents extra._

  IRRITABILITY.
       A PHYSIOLOGICAL ANALYSIS OF THE GENERAL EFFECT OF
       STIMULI IN LIVING SUBSTANCES.
    _By_ MAX VERWORN,
    _Professor at Bonn Physiological Institute_.
  _Price $3.50 net; postage 20 cents extra._

  THE EVOLUTION OF MODERN MEDICINE.
    _By_ SIR WILLIAM OSLER, BART., M.D., LL.D., SC.D.,
    _Regius Professor of Medicine, Oxford University_.
  _Price $3.00 net; postage 40 cents extra._




                     PROBLEMS OF GENETICS

                              BY
                 WILLIAM BATESON, M.A., F.R.S.

        DIRECTOR OF THE JOHN INNES HORTICULTURAL INSTITUTION,
            HON. FELLOW OF ST. JOHN'S COLLEGE, CAMBRIDGE,
        AND FORMERLY PROFESSOR OF BIOLOGY IN THE UNIVERSITY

                     _WITH ILLUSTRATIONS_

                         [Illustration]

                NEW HAVEN: YALE UNIVERSITY PRESS
                    LONDON: HUMPHREY MILFORD
                     OXFORD UNIVERSITY PRESS

                             MCMXIII


                         Copyright, 1913
                       By YALE UNIVERSITY

                First printed August, 1913, 1000 copies


[** Transcriber's Note:
     Underscores "_" before and after a word or phrase indicate ITALICS
       in the original text.
     Hyphenation was used inconsistently by the author and has been
        left as in the original text. ]




                    THE SILLIMAN FOUNDATION

In the year 1883 a legacy of about eighty-five thousand dollars was left
to the President and Fellows of Yale College in the city of New Haven,
to be held in trust, as a gift from her children, in memory of their
beloved and honored mother, Mrs. Hepsa Ely Silliman.

On this foundation Yale College was requested and directed to establish
an annual course of lectures designed to illustrate the presence and
providence, the wisdom and goodness of God, as manifested in the natural
and moral world. These were to be designated as the Mrs. Hepsa Ely
Silliman Memorial Lectures. It was the belief of the testator that any
orderly presentation of the facts of nature or history contributed
to the end of this foundation more effectively than any attempt to
emphasize the elements of doctrine or of creed; and he therefore
provided that lectures on dogmatic or polemical theology should be
excluded from the scope of this foundation, and that the subjects should
be selected rather from the domains of natural science and history,
giving special prominence to astronomy, chemistry, geology, and anatomy.

It was further directed that each annual course should be made the basis
of a volume to form part of a series constituting a memorial to Mrs.
Silliman. The memorial fund came into the possession of the Corporation
of Yale University in the year 1901; and the present volume constitutes
the fifth of the series of memorial lectures.




                           PREFACE

This book gives the substance of a series of lectures delivered in Yale
University, where I had the privilege of holding the office of Silliman
Lecturer in 1907.

The delay in publication was brought about by a variety of causes.

Inasmuch as the purpose of the lectures is to discuss some of the wider
problems of biology in the light of knowledge acquired by Mendelian
methods of analysis, it was essential that a fairly full account of
the conclusions established by them should first be undertaken and I
therefore postponed the present work till a book on Mendel's Principles
had been completed.

On attempting a more general discussion of the bearing of the phenomena
on the theory of Evolution, I found myself continually hindered by the
consciousness that such treatment is premature, and by doubt whether
it were not better that the debate should for the present stand
indefinitely adjourned. That species have come into existence by an
evolutionary process no one seriously doubts; but few who are familiar
with the facts that genetic research has revealed are now inclined to
speculate as to the manner by which the process has been accomplished.
Our knowledge of the nature and properties of living things is far too
meagre to justify any such attempts. Suggestions of course can be made:
though, however, these ideas may have a stimulating value in the lecture
room, they look weak and thin when set out in print. The work which may
one day give them a body has yet to be done.

The development of negations is always an ungrateful task apt to be
postponed for the positive business of experiment. Such work is happily
now going forward in most of the centers of scientific life. Of many
of the subjects here treated we already know more than we did in 1907.
The delay in production has made it possible to incorporate these new
contributions.

The book makes no pretence at being a treatise and the number of
illustrative cases has been kept within a moderate compass. A good many
of the examples have been chosen from American natural history, as being
appropriate to a book intended primarily for American readers. The facts
are largely given on the authority of others, and I wish to express my
gratitude for the abundant assistance received from American colleagues,
especially from the staffs of the American Museum in New York, and of
the Boston Museum of Natural History. In connexion with the particular
subjects personal acknowledgments are made.

Dr. F. M. Chapman was so good as to supervise the preparation of the
 Plate of _Colaptes_, and to authorize the loan of the Plate
representing the various forms of _Helminthophila_, which is taken from
his _North American Warblers_.

I am under obligation to Messrs. Macmillan & Co., for permission to
reproduce several figures from _Materials for the Study of Variation_,
illustrating subjects which I wished to treat in new associations, and
to M. Leduc for leave to use Fig. 9.

In conclusion I thank my friends in Yale for the high honour they did me
by their invitation to contribute to the series of Silliman Lectures,
and for much kindness received during a delightful sojourn in that
genial home of learning.




                    TABLE OF CONTENTS.

  CHAPTER                                                  PAGE

     I. INTRODUCTORY. THE PROBLEM OF SPECIES AND VARIETY     1
    II. MERISTIC PHENOMENA                                  31
   III. SEGMENTATION, ORGANIC AND MECHANICAL                60
    IV. THE CLASSIFICATION OF VARIATION AND THE NATURE
                OF SUBSTANTIVE VARIATION                    83
        NOTE TO CHAPTER IV                                  94
     V. THE MUTATION THEORY                                 97
        NOTE TO CHAPTER V                                  116
    VI. VARIATION AND LOCALITY                             118
   VII. LOCAL DIFFERENTIATION--_continued_.
              OVERLAPPING FORMS                            146
  VIII. LOCALLY DIFFERENTIATED FORMS--_continued_.
              CLIMATIC VARIETIES                           164
    IX. THE EFFECTS OF CHANGED CONDITIONS                  187
     X. THE EFFECTS OF CHANGED CONDITIONS--_continued_.
              THE CAUSES OF GENETIC VARIATION              212
    XI. THE STERILITY OF HYBRIDS. CONCLUDING REMARKS       233
        APPENDIX TO CHAPTER X                              250
        INDEX                                              251






                        PROBLEMS OF GENETICS




                              CHAPTER I

                             INTRODUCTORY

The purpose of these lectures is to discuss some of the familiar
phenomena of biology in the light of modern discoveries. In the last
decade of the nineteenth century many of us perceived that if any
serious advance was to be made with the group of problems generally
spoken of as the Theory of Evolution, methods of investigation must be
devised and applied of a kind more direct and more penetrating than
those which after the general acceptance of the Darwinian views had been
deemed adequate. Such methods obviously were to be found in a critical
and exhaustive study of the facts of variation and heredity, upon which
all conceptions of evolution are based. To construct a true synthetic
theory of Evolution it was necessary that variation and heredity instead
of being merely postulated as axioms should be minutely examined as
phenomena. Such a study Darwin himself had indeed tentatively begun, but
work of a more thorough and comprehensive quality was required. In the
conventional view which the orthodoxy of the day prescribed, the terms
variation and heredity stood for processes so vague and indefinite that
no analytical investigation of them could be contemplated. So soon,
however, as systematic inquiry into the natural facts was begun it was
at once found that the accepted ideas of variation were unfounded.
Variation was seen very frequently to be a definite and specific
phenomenon, affecting different forms of life in different ways, but
in all its diversity showing manifold and often obvious indications
of regularity. This observation was not in its essence novel. Several
examples of definite variation had been well known to Darwin and
others, but many, especially Darwin himself in his later years, had
nevertheless been disposed to depreciate the significance of such
facts. They consequently then lapsed into general disparagement. Upon
more careful inquiry the abundance of such phenomena proved to be far
greater than was currently supposed, and a discussion of their nature
brought into prominence a consideration of greater weight, namely that
the differences by which these definite or discontinuous variations are
constituted again and again approximate to and are comparable with the
class of differences by which species are distinguished from each other.

The interest of such observations could no longer be denied. The
more they were examined the more apparent it became that by means of
the facts of variation a new light was obtained on the physiological
composition and capabilities of living things. Genetics thus cease to be
merely a method of investigating theories of evolution or of the origin
of species but provide a novel and hitherto untried instrument by which
the nature of the living organism may be explored. Just as in the study
of non-living matter science began by regarding the external properties
of weight, opacity, colour, hardness, mode of occurrence, etc., noting
only such evidences of chemical attributes and powers as chance
spontaneously revealed; and much later proceeded to the discovery that
these casual manifestations of chemical properties, rightly interpreted,
afford a key to the intrinsic nature of the diversity of matter, so in
biology, having examined those features of living things which ordinary
observations can perceive, we come at last to realize that when studied
for their own sake the properties of living organisms in respect of
heredity and variation are indications of their inner nature and provide
evidences of that nature which can be obtained from no other source.

While such ideas were gradually forming in our minds, came the
rediscovery of Mendel's work. Investigations which before had only
been imagined as desirable now became easy to pursue, and questions
as to the genetic inter-relations and compositions of varieties can
now be definitely answered. Without prejudice to what the future may
disclose whether by way of limitation or extension of Mendelian method,
it can be declared with confidence and certainty that we have now the
means of beginning an analysis of living organisms, and distinguishing
many of the units or factors which essentially determine and cause the
development of their several attributes.

Briefly put, the essence of Mendelism lies in the discovery of the
existence of unit characters or factors. For an account of the Mendelian
method, how it is applied and what it has already accomplished,
reference must be made to other works.[1] With this part of the subject
I shall assume a sufficient acquaintance. In these lectures I have
rather set myself the task of considering how certain problems appear
when viewed from the standpoint to which the application of these
methods has led us. It is indeed somewhat premature to discuss such
questions. The work of Mendelian analysis is progressing with great
rapidity and anything I can say may very soon be superseded as out
of date. Nevertheless a discussion of this kind may be of at least
temporary service in directing inquiry to the points of special interest.


             THE PROBLEM OF SPECIES AND VARIETY

Nowhere does our new knowledge of heredity and variation apply more
directly than to the problem what is a species and what is a variety? I
cannot assert that we are already in a position to answer this important
question, but as will presently appear, our mode of attack and the
answers we expect to receive are not those that were contemplated by our
predecessors. If we glance at the history of the scientific conception
of Species we find many signs that it was not till comparatively recent
times that the definiteness of species became a strict canon of the
scientific faith and that attempts were made to give precise limits
to that conception. When the diversity of living things began to be
accurately studied in the sixteenth and seventeenth centuries names
were applied in the loosest fashion, and in giving a name to an animal
or a plant the naturalists of those times had no ulterior intention.
Names were bestowed on those creatures about which the writer proposed
to speak. When Gesner or Aldrovandi refer to all the kinds of horses,
unicorns, dogs, mermaids, etc., which they had seen or read of, giving
to each a descriptive name, they do not mean to "elevate" each named
kind to "specific rank"; and if anyone had asked them what they meant by
a species, it is practically certain that they would have had not the
slightest idea what the question might imply, or any suspicion that it
raised a fundamental problem of nature.

Spontaneous generation being a matter of daily observation, then
unquestioned, and supernatural events of all kinds being commonly
reported by many witnesses, transmutation of species had no inherent
improbability. Matthioli,[2] for instance, did not expect to be charged
with heresy when he declared _Stirpium mutatio_ to be of ordinary
occurrence. After giving instances of induced modifications he wrote,
"Tantum enim in plantis naturae germanitas potest, ut non solum saepe
praedictos praestet effectus, sed etiam ut alteram in alteram stirpem
facile vertat, ut cassiam in cinnamomum, sisymbrium in mentham, triticum
in lolium, hordeum in avenam, et ocymum in serpyllum."

I do not know who first emphasized the need for a clear understanding
of the sense in which the term species is to be applied. In the second
half of the seventeenth century Ray shows some degree of concern on
this matter. In the introduction to the _Historia Plantarum_, 1686, he
discusses some of the difficulties and lays down the principle that
varieties which can be produced from the seed of the same plant are to
be regarded as belonging to one species, being, I believe, the first
to suggest this definition. That new species can come into existence
he denies as inconsistent with Genesis 2, in which it is declared that
God finished the work of Creation in six days. Nevertheless he does not
wholly discredit the possibility of a "transmutation" of species, such
that one species may as an exceptional occurrence give rise by seed
to another and nearly allied species. Of such a phenomenon he gives
illustrations the authenticity of which he says he is, against his will,
compelled to admit. He adds that some might doubt whether in the cases
quoted the two forms concerned are really distinct species, but the
passage is none the less of value for it shews that the conception of
species as being distinct unchangeable entities was not to Ray the dogma
sacrosanct and unquestionable which it afterwards became.[3]

In the beginning of the eighteenth century Marchant,[4] having observed
the sudden appearance of a lacinated variety of _Mercurialis_, makes the
suggestion that species in general may have arisen by similar mutations.
Indeed from various passages it is manifest that to the authors of the
seventeenth and early eighteenth centuries species appeared simply as
groups more or less definite, the boundaries of which it was unnecessary
to determine with great exactitude. Such views were in accord with the
general scientific conception of the time. The mutability of species is
for example sometimes likened (see for instance Sharrock, loc. cit.) to
the metamorphoses of insects, and it is to be remembered that the search
for the Philosopher's Stone by which the transmutation of metals was to
be effected had only recently fallen into discredit as a pursuit.

The notion indeed of a peculiar, fixed meaning to be attached to species
as distinct from variety is I think but rarely to be found categorically
expressed in prae-Linnaean writings.

But with the appearance of the _Systema Naturae_ a great change
supervened. Linnaeus was before all a man of order. Foreseeing the
immense practical gain to science that must come from a codification of
nomenclature, he invented such a system.

It is not in question that Linnaeus did great things for us and made
Natural History a manageable and accessible collection of facts instead
of a disorderly heap; but orderliness of mind has another side, and
inventors and interpreters of systems soon attribute to them a force and
a precision which in fact they have not.

The systematist is primarily a giver of names, as Ray with his broader
views perceived. Linnaeus too in the exordium to the _Systema Naturae_
naively remarks, that he is setting out to continue the work which
Adam began in the Golden Age, to give names to the living creatures.
Naming however involves very delicate processes of mind and of logic.
Carried out by the light of meagre and imperfect knowledge it entails
all the mischievous consequences of premature definition, and promotes
facile illusions of finality. So was it with the Linnaean system. An
interesting piece of biological history might be written respecting the
growth and gradual hardening of the conception of Species. To readers
of Linnaeus's own writings it is well known that his views cannot be
summarized in a few words. Expressed as they were at various times
during a long life and in various connexions, they present those divers
inconsistencies which commonly reflect a mind retaining the power of
development. Nothing certainly could be clearer than the often quoted
declaration of the _Philosophia Botanica_, "Species tot numeramus quot
diversae formae in principio sunt creatae," with the associated passage
"Varietates sunt plantae ejusdem speciei mutatae a caussa quacunque
occasionali." Those sayings however do not stand alone. In several
places, notably in the famous dissertation on the peloric _Linaria_
he explicitly contemplates the possibility that new species may arise
by crossing, declaring nevertheless that he thinks such an event to
be improbable. In that essay he refers to Marchant's observation on a
laciniate _Mercurialis_, but though he states clearly that that plant
should only be regarded as a variety of the normal, he does not express
any opinion that the contemporary genesis of new species must be an
impossibility. In the later dissertation on Hybrid Plants he returns to
the same topic. Again though he states the belief that species cannot
be generated by cross-breedings, he treats the subject not as heretical
absurdity but as one deserving respectful consideration.

The significance of the aphorisms that precede the lectures on the
Natural Orders is not easy to apprehend. These are expressed with the
utmost formality, and we cannot doubt that in them we have Linnaeus's
own words, though for the record we are dependent on the transcripts of
his pupils.

   The text of the first five is as follows:

   1. Creator T. O. in primordio vestiit Vegetabile _Medullare_
   principiis constitutivis diversi _Corticalis_ unde tot difformia
   individua, quot _Ordines_ Naturales prognata.

   2. _Classicas_ has (1) plantas Omnipotens miscuit inter se,
   unde tot _Genera_ ordinum, quot inde plantae.

   3. _Genericas_ has (2) miscuit Natura, unde tot _Species_
   congeneres quot hodie existunt.

   4. _Species_ has miscuit Casus, unde totidem quot passim
   occurrunt, _Varietates_.

   5. Suadent haec (1-4) Creatoris leges a simplicibus ad
   Composita.

   Naturae leges generationis in hybridis.

   Hominis leges ex observatis a posteriori.

I am not clear as to the parts assigned in the first sentence
respectively to the "_Medulla_" and the "_Cortex_," beyond that Linnaeus
conceived that multiformity was first brought about by diversity in
the "_Cortex_." The passage is rendered still more obscure if read in
connection with the essay on "_Generatio Ambigena_," where he expresses
the conviction that the _Medulla_ is contributed by the mother, and the
_Cortex_ by the father, both in plants and animals.[5]

But however that may be, he regards this original diversity as resulting
in the constitution of the Natural Orders, each represented by one
individual.

In the second aphorism the Omnipotent is represented as creating the
genera by intermixing the individual _plantae classicae_, or prototypes
of the Natural Orders.

The third statement is the most remarkable, for in it he declares that
Species were formed by the act of Nature, who by inter-mixing the genera
produced _Species congeneres_, namely species inside each genus, to the
number which now exist. Lastly, Chance or Accident, intermixing the
species, produced as many varieties as there are about us.

Linnaeus thus evidently regarded the intermixing of an originally
limited number of types as the sufficient cause of all subsequent
diversity, and it is clear that he draws an antithesis between
_Creator_, _Natura_, and _Casus_, assigning to each a special part
in the operations. The acts resulting in the formation of genera are
obviously regarded as completed within the days of the Creation, but the
words do not definitely show that the parts played by Nature and Chance
were so limited.

Recently also E. L. Greene[6] has called attention to some curious
utterances buried in the _Species Plantarum_, in which Linnaeus refers
to intermediate and transitional species, using language that even
suggests evolutionary proclivities of a modern kind, and it is not easy
to interpret them otherwise.

Whatever Linnaeus himself believed to be the truth, the effect of his
writings was to induce a conviction that the species of animals and
plants were immutably fixed. Linnaeus had reduced the whole mass of
names to order and the old fantastical transformations with the growth
of knowledge had lapsed into discredit; the fixity of species was
taken for granted, but not till the overt proclamation of evolutionary
doctrine by Lamarck do we find the strenuous and passionate assertions
of immutability characteristic of the first half of the nineteenth
century.

It is not to be supposed that the champions of fixity were unacquainted
with varietal differences and with the problem thus created, but in
their view these difficulties were apparent merely, and by sufficiently
careful observation they supposed that the critical and permanent
distinctions of the true species could be discovered, and the
impermanent variations detected and set aside.

This at all events was the opinion formed by the great body of
naturalists at the end of the eighteenth and beginning of the nineteenth
centuries, and to all intents and purposes in spite of the growth of
evolutionary ideas, it remains the guiding principle of systematists
to the present day. There are 'good species' and 'bad species' and the
systematists of Europe and America spend most of their time in making
and debating them.

In some of its aspects the problem of course confronted earlier
naturalists. Parkinson for instance (1640) in introducing his treatment
of _Hieracium_ wrote, "To set forth the whole family of the Hawkeweedes
in due forme and order is such a world of worke that I am in much doubt
of mine own abilitie, it having