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Hormones and Heredity

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Juliet Sutherland, Charles Bidwell
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HORMONES AND HEREDITY

A Discussion Of The Evolution Of Adaptations
And The Evolution Of Species


By J. T. CUNNINGHAM, M.A. (OXON), F.Z.S.

Sometime Fellow of University College, Oxford
Lecturer in zoology at East London College, University of London


LONDON
CONSTABLE AND CO. LTD.
1921



PREFACE

My chief object in writing this volume was to discuss the relations of
modern discoveries concerning hormones or internal secretions to the
question of the evolution of adaptations, and on the other hand to the
results of recent investigations of Mendelian heredity and mutations. I
have frequently found, from verbal or written references to my opinions,
that the evidence on these questions and my own conclusions from that
evidence were either imperfectly known or misunderstood. This is not
surprising in view of the fact that hitherto my only publications on the
hormone theory have been a paper in a German periodical and a chapter in
an elementary text-book. The present publication is by no means a thorough
or complete exposition of the subject, it is merely an attempt to state
the fundamental facts and conclusions, the importance of which it seems to
me are not generally appreciated by biologists.

I have reviewed some of the chief of the recent discoveries concerning
mutations, Mendelism, chromosomes, etc., but have not thought it necessary
to repeat the illustrations which are contained in many of the volumes to
which I have referred. I have made some Mendelian experiments myself, not
always with results in agreement with the strict Mendelian doctrine, so
that I am not venturing to criticise without experience. I have not
hesitated to reprint the figure, published many years ago, of a Flounder
showing the production of pigment under the influence of light, because I
thought it was desirable that the reader should have before him this
figure and those of an example of mutation in the Turbot for comparison
when following the argument concerning mutation and recapitulation.

I take this opportunity of expressing my thanks to the Councils of the
Royal Society and the Zoological Society for permission to reproduce the
figures in the Plates. I also desire to thank Professor Dendy, F.R.S., of
King's College for his sympathetic interest in the publication of the
book, and Messrs. Constable and Co. for the care they have taken in its
production.

J. T. CUNNINGHAM.
London, _June_ 1921.



CONTENTS

INTRODUCTION - Historical Survey Of Theories Or Suggestions Of Chemical
Influence In Heredity

CHAPTER I - Classification And Adaptation

CHAPTER II - Mendelism And The Heredity Of Sex

CHAPTER III - Influence Of Hormones On Development Of Somatic
Sex-Characters

CHAPTER IV - Origin Of Somatic Sex-Characters In Evolution

CHAPTER V - Mammalian Sexual Characters,
Evidence Opposed To The Hormone Theory

CHAPTER VI - Origin Of Non-Sexual Characters: The Phenomena Of Mutation

CHAPTER VII - Metamorphosis and Recapitulation

INDEX


LIST OF PLATES

PLATE I. Recessive Pile Fowls

PLATE II. Abnormal Specimen Of Turbot

PLATE III. Flounder, Showing Pigmentation Of Lower Side
After Exposure To Light



INTRODUCTION

Historical Survey Of Theories Or Suggestions Of
Chemical Influence In Heredity

Weismann, strongly as he denied the possibility of the transmission of
somatic modifications, admitted the possibility or even the fact of the
simultaneous modification of soma and germ by external conditions
such as temperature. Yves Delage [Footnote: Yves Delage, _L'Hérédité_
(Paris, 1895), pp. 806-812.] in 1895, in discussing this question, pointed
out how changes affecting the soma would produce an effect on the ovum
(and presumably in a similar way on the sperm). He writes:--

'Ce qui empêche l'oeuf de recevoir la modification reversible c'est
qu'étant constitué autrement que les cellules différenciées de l'organisme
il est influencé autrement qu'elles par les mêmes causes perturbatrices.
Mais est-il impossible que malgré la différence de constitution
physico-chimiques il soit influencé de la même façon?'

The author's meaning would probably have been better expressed if he had
written 'ce qui paraît empêcher.' By 'modification reversible' he means a
change in the ovum which will produce in the next generation a somatic
modification similar to that by which it was produced. It seems natural to
think of the influence of the ovum on the body and of the body on the ovum
as of similar kind but in opposite directions, but it must be remembered
always that the development of the body from the ovum Is not an influence
at all but a direct conversion by cell-division and differentiation of the
ovum into the body.

Delage argues that if the egg contains the substances characteristic of
certain categories of cells of the organism it ought to be affected at the
same time as those cells and by the same agents. He thinks that the egg
only contains the substances or the arrangements characteristic of certain
general functions (nervous, muscular, perhaps glandular of divers kinds)
but without attribution to localised organs. In his view there is no
representation of parts or of functions in the ovum, but a simple
qualitative conformity of constitution between the egg and the categories
of cells which in the body are charged with the accomplishment of the
principal functions. Thus mutilations of organs formed of tissues
occurring also elsewhere in the body cannot be hereditary, but if the
organ affected contains the whole of a certain kind of tissue such as
liver, spleen, kidney, then the blood undergoes a qualitative modification
which reacts on the constitution of the egg.

Suppose the internal secretion of a gland (_e.g._ glucose for the liver,
glycolytic for the ferment for the pancreas) is the physiological excitant
for the gland. If the gland is removed in whole or in part the proportion
of its internal secretion in the blood will be diminished. Then the gland,
if the suppression is partial, will undergo a new diminution of activity
But in, the egg the specific substance of the gland will also be less
stimulated, and in the next generation a diminution of the gland may
result. Thus Delage states Massin found that partial removal of the liver
in rabbits had an inherited effect. In the case of excretory glands the
contrary will be the case, for their removal causes increase in the blood
of the exciting urea and uric acid.

The effects of disuse are similar to those of mutilations and of use vice
versa. Delage, as seen above, does not consider that increase or decrease
of particular muscles can be inherited, but only the muscular system in
general. If, however, in consequence of the disuse of a group of muscles
there was a general diminution of the inherited muscular system, the
special group would remain diminished while the rest were developed by use
in the individual: there would thus be a heredity produced indirectly.
With regard to general conditions of life, Delage states that there are
only two of which we know anything--namely, climate and alimentation--and
he merely suggests that temperature and food act at the same time on the
cells of the body and on the similar substances in the egg.

H. M. Vernon (_Variation in Animals and Plants_, 1903, pp. 351 _seq._)
cites instances of the cumulative effects of changed conditions of life,
and points out that they are not really instances of the inheritance of
acquired characters, but merely of the germ-plasm and the body tissues
being simultaneously affected. He then asks, Through what agency is the
environment enabled to act on the germ-plasm? And answers that the only
conceivable one is a chemical influence through products of metabolism
and specific internal secretions. He cites several cases of specific
internal secretions, making one statement in particular which seems
unintelligible, viz. that extirpation of the total kidney substance of a
dog leads not to a diminished secretion of urine but to a largely
increased secretion accompanied by a rapid wasting away which soon ends
fatally.

Whenever a changed environment acts upon the organism, therefore, it to
some extent affects the normal excretions and secretions of some or all of
the various tissues, and these react not only on the tissues themselves,
but also to a less degree upon the determinants representing them in the
germ-plasm. Thus the relative size of the brain has decreased in the tame
rabbit. This may be due to disuse; the excretions and secretions of the
nervous tissues would be diminished, and the corresponding determinants
less stimulated. Another instance is afforded by pigmentation of the skin
in man; which varies with the amount of light and heat from the sun to
which the skin is exposed. Specific excretory products of pigment in the
skin may stimulate the pigment determinants in the germ-plasm to vigour.
But only those characters of which the corresponding tissues possess a
specific secretion or excretion could become hereditary in this way. For
instance, the brawny arm of the blacksmith could not be transmitted, as it
is scarcely possible that the arm muscles can have a secretion different
from that of the other muscles.

In 1904, P. Schiefferdecker
[Footnote: P. Schiefferdecker, _Ueber Symbiose_. S.B. d. Niederrhein.
Gesellsch. zu Bonn. Sitzung der Medicinischen Sektion, 13 Juni 1904.]
made the definite suggestion that the presence of specific internal
secretions could be very well used for the explanation of the inheritance
of acquired characters. When particular parts of the body were changed,
these modifications must change the mixture of materials in the blood by
the substances secreted by the changed parts. Thereby would be found a
connexion between the modified parts of the body and the germ-cells, the
only connexion in existence. It is to be assumed, according to this
author, that only a qualitative change in the nutritive fluid of the
germ-cells could produce an effect: a quantitative change would only cause
increased or decreased nourishment of the entire germ cells.

In my own volume on _Sexual Dimorphism in the Animal Kingdom_, published
in 1900, I attempted to explain the limitation of secondary sexual
characters not only to one sex, but usually to one period of the
individual life, namely, that of sexual maturity; and in some cases, as in
male Cervidae, to one season of the year in which alone the sexual organs
are active. It had been known for centuries that the normal development of
male sexual characters did not take place in castrated animals, but the
exact nature of the influence of the male generative organs on that
development was not known till a year or two later than 1900, when it was
shown to be due to an internal secretion. My argument was that all
selection theories failed to account for the limitation of secondary
sexual characters in heredity, whereas the Lamarckian theory would explain
them if the assumption were made that the effects of stimulation having
been originally produced when the body and tissues were under the
influence of the sexual organs in functional activity, these effects were
only developed in heredity when the body was in the same condition.

About the year 1906, when preparing two special lectures in London
University on the same subject, I became acquainted with the work of
Starling and others on internal secretions or hormones, and saw at once
that the hormone from the testes was the actual agent which constituted
the 'influence' assumed by me in 1900. In these lectures I elaborated a
definite Lamarckian theory of the origin of Secondary Sexual Characters in
relation to Hormones, extending the theory also to ordinary adaptive
structures and characters which are not related to sex. Having met with
many obstacles in endeavouring to get a paper founded on the original
lectures published in England, I finally sent it to Professor Wilhelm
Roux, the editor of the _Archiv für Entwicklungsmechanik der Organismen_,
in which it was published in 1908.

In his volume on the Embryology of the Invertebrata, 1914 (_Text-Book of
Embryology_, edited by Walter Heape, vol. i.), Professor E. W. MacBride in
his general summary (chapter xviii.) puts forward suggestions concerning
hormones without any reference to those who have discussed the subject
previously. He considers the matter from the point of view of development,
and after indicating the probability that hormones are given off by all
the tissues of the body, gives instances of organs being formed in
regeneration (eye of shrimp) or larvae (common sea-urchin) as the result
of the presence of neighbouring organs, an influence which he thinks can
only be due to a hormone given off by the organ already present. He then
states that Professor Langley had pointed out to him in correspondence
that if an animal changes its structure in response to a changed
environment, the hormones produced by the altered organs will be changed.
The altered hormones will circulate in the blood and bathe the growing and
maturing genital cells. Sooner or later, he assumes, some of these
hormones may become incorporated in the nuclear matter of the genital
cells, and when these cells develop into embryos the hormones will be set
free at the corresponding period of development at which they were
originally formed, and reinforce the action of the environment. In this
way MacBride attempts to explain recapitulation in development and the
tendency to precocity in the development of ancestral structures. His idea
that the hormones act by 'incorporation' in the genital cells is different
from that of stimulation of determinants put forward by myself and others,
but it is surprising that he should refer to unpublished suggestions of
Professor Langley, and not to the publications of authors who had
previously discussed the possible action of hormones in connexion with the
heredity of somatic modifications.

Dr. J. G. Adami in 1918 published the Croonian Lectures, delivered by him
in 1917 under the title 'Adaptation and Disease,' together with reprints
of previous papers, in a volume entitled _Medical Contributions to the
Study of Evolution_. In this work (footnote, p. 71) the author claims
that he preceded Professor Yves Delage by some two years in offering a
physico-chemical hypothesis in place of determinants, and also asserts
that 'the conclusions reached by him in 1901 regarding metabolites and, as
we subsequently became accustomed to term them, hormones, and their
influence on the germ-cells, have since been enunciated by Heape, Bourne,
Cunningham, MacBride, and Dendy, although in each case without note of his
(Adami's) earlier contribution.' These somewhat extensive claims deserve
careful and impartial examination. The paper to which Dr. Adami refers was
an Annual Address to the Brooklyn Medical Club, published in the _New York
Medical Journal_ and the _British Medical Journal_ in 1901, and entitled
'On Theories of Inheritance, with special reference to Inheritance of
Acquired Conditions in Man.' The belief that this paper had two years'
priority over the volume of Delage entitled _L'Hérédité_ appears to have
arisen from the fact that Adami consulted the bibliographical list in
Thomson's compilation, _Heredity_ 1908, where the date of Delage's work is
as 1903. But this was the second edition, the first having been published,
as quoted above, in 1895, six years before the paper by Adami.

Next, with regard to the claim that Adami's views as stated in the paper
to which he refers were essentially the same as those brought forward
by myself and others many years later, we find on reading the paper that
its author discussed merely the effect of toxins in disease upon the
body-cells and the germ-cells, causing in the offspring either various
forms of arrested and imperfect development or some degree of immunity. In
the latter case he argues that the action of the toxin of the disease has
been to set up certain molecular changes, certain alterations in the
composition of the cell-substance so that the latter responds in a
different manner when again brought into contact with the toxin. Once this
modification in the cell-substance is produced the descendants of this
cell retain the same properties, although not permanently. Inheritance of
the acquired condition has to be granted, he says, in the case of the
body-cells in such cases. But this is not the question: inheritance in the
proper sense of the word means the transmission to individuals of the next
generation.

On this point Adami says we must logically admit the action of the toxins
on the germ-cells, and the individuals developed from these must, subject
to the law of loss already noted, have the same properties. He admits that
inherited immunity is rare, but says that it has occasionally been noted.
Here we have again merely the same influence, chemical in this case,
acting simultaneously on somatic cells and germ-cells, which is not
the inheritance of acquired characters at all. Adami remarks that Weismann
would make the somewhat subtle distinction that the toxins produce these
results not by acting on the body-cells but by direct action on the
germ-cells, that the inheritance is blastogenic not somatogenic, and calls
this 'a sorry and almost Jesuitic play upon words.' On the contrary, it is
the essential point, which Adami fails to appreciate. However, he goes
further and refers to endogenous intoxication, to disturbed states of the
constitution, due to disturbances in glandular activity or to excess of
certain internal secretions. Such disturbances he says, acting on the
germ-cells, would be truly somatogenic. In the case of gout he considers
that defect in body metabolism has led to intoxication of the germ-cells,
and the offspring show a peculiar liability to be the subjects of
intoxications of the same order. Now, however important these views
and conclusions may be from the medical point of view, in relation to
the heredity of general physiological or pathological conditions,
they throw no light on the problems considered by myself and other
biologists--namely, the origin of species and of structural adaptations.

There is no mention anywhere in Adami's short paper of the evolution or
heredity of structural characters or adaptations such as wing of Bird or
Bat, lung of Frog, asymmetry of Flat-fish or of specific characters, still
less of secondary sexual characters, which formed the basis of the hormone
theory in my 1908 paper. He does not even consider the evolution of the
structural adaptations which enable man to maintain the erect position on
the two hind-limbs. He does not consider the action of external
stimulation, whether the direct action on epidermal or other external
structures or the indirect action through stimulation of functional
activity. All his examples of external agents are toxins produced by
bacteria invading the body, except in the case of gout, for which he
suggests no external cause at all.

Only once in the last of the part of the paper considered does Adami
mention internal secretions. His actual words are: 'We recognise yearly
more and more the existence of auto-intoxications, of disturbed states of
the constitution due to disturbances in glandular activity or to excess of
certain internal secretions or of the substances ordinarily neutralised by
the same.' The only example he gives is that of gout. How remote this is
from the discoveries concerning the specific action of hormones on the
growth of the body or of special parts of the body, or on the function of
glands, and from a definite hormone theory of heredity as proposed by
myself, is sufficiently obvious.



CHAPTER I

Classification And Adaptation


The study of the animals and plants now living on the earth naturally
divides itself into two branches, the one being concerned with their
structure and classification, the other with their living activities,
their habits, life histories, and reproduction. Both branches are usually
included under the terms Natural History, or Zoology, or Botany, and a
work on any group of animals usually attempts to describe their structure,
their classification, and their habits. But these two branches of
biological science are obviously distinct in their methods and aims, and
each has its own specialists. The pursuit, whose ultimate object is to
distinguish the various kinds of organisms and show their true and not
merely apparent relations to one another in structure and descent,
requires large collections of specimens for comparison and reference: it
can be carried on more successfully in the museum than among the animals
or plants in their natural surroundings. This study, which may be called
Taxonomics, deals, in fact, with organisms as dead specimens, and it
emphasises especially the distinguishing characters of the ultimate
subdivisions of the various tribes of animals and plants--namely, species
and varieties. The investigation, on the other hand, of the different
modes of life of animals or plants is based on a different mental
conception of them: it regards them primarily as living active organisms,
not as dead and preserved specimens, and it can only be carried on
successfully by observing them in their natural conditions, in the wide
spaces of nature, under the open sky.

The object of this kind of inquiry is to ascertain what are the uses of
organs or structures, what they are for, as we say in colloquial language,
to discover what are their functions and how these functions are useful or
necessary to the life of the animals or plants to which they belong. For
example, some Cuttle-fishes or Cephalopoda have eight arms or tentacles
and others ten. The taxonomist notices the fact and distinguishes the two
groups of Octopoda and Decapoda.

But it is also of interest to ascertain what is the use of the two
additional arms in the Decapoda. They differ from the other arms in being
much longer, and provided with sockets into which they can be retracted,
and suckers on them are limited to the terminal region. In the majority of
zoological books in which Cephalopoda are described, nothing is said of
the use or function of these two special arms. Observation of the living
animal in aquaria has shown that their functions is to capture active prey
such as prawns. They act as a kind of double lasso. Sepia, for instance,
approaches gently and cautiously till it is within striking distance of a
prawn, then the two long tentacles are suddenly and swiftly shot out from
their sockets and the prawn is caught between the suckers at the ends of
them. Another example is afforded by the masked crab (_Corystes
cassivelaunus_). This species has unusually long and hairy antennae. These
are usually tactile organs, but it has been found that the habit of
_Corystes_ is to bury itself deep in the sand with only the tips of the
antennae at the surface, and the two are placed close together so as to
form a tube, down which a current of water, produced by movements of
certain appendages, passes to the gill chamber and provides for the
respiration of the crab while it is buried, to a depth of two or three
inches. The results of the investigation of habits and functions may be
called Bionomics. It may be aided by scientific institutions specially
designed to supplement mere observation in the field, such as menageries,
aquaria, vivaria, marine laboratories, the objects of which are to bring
the living organism under closer and more accurate observation. The
differences between the methods and results of these two branches of
Biology may be illustrated by comparing a British Museum Catalogue with
one of Darwin's studies, such as the 'Fertilisation of Orchids' or
'Earthworms.'

Other speculations in Biology are related to Taxonomics or Bionomics
according as they deal with the structure of the dead organism or the
action of the living. Anatomy and its more theoretical interpretation,
morphology, are related to Taxonomics, physiology and its branches to
Bionomics. In fact, the fundamental principles of physiology must be
understood before the study of Bionomics can begin. We must know the
essential nature of the process of respiration before we can appreciate
the different modes of respiration in a whale and a fish, an aquatic
insect and a crustacean. The more we know of the physiology of
reproduction, the better we can understand the sexual and parental habits
of different kinds of animals.

The two branches of biological study which we are contrasting cannot,
however, be completely separated even by those whose studies are most
specialised. In Bionomics it is necessary to distinguish the types which
are observed, and often even the species, as may be illustrated by the
fact that controversies occasionally arise among amateur and even
professional fishermen on the question whether dog-fishes are viviparous
or oviparous, the fact being that some species are the one and others the
other, or the fact that the harmless slow-worm and ring-snake are dreaded
and killed in the belief that they are venomous snakes. Taxonomics, on the
other hand, must take account of the sex of its specimens, and the changes
of structure that an individual undergoes in the course of its life, and
of the different types that may be normally produced from the same
parents, otherwise absurd errors are perpetrated. The young, the male, and
the female of the same species have frequently been described under
different names as distinct species or even genera. For example, the larva
of marine crabs was formerly described as a distinct genus under the name
of _Zoaea_, and in the earlier part of the nineteenth century a lively
controversy on the question was carried on between a retired naval surgeon
who hatched _Zoaea_ from the eggs of crabs, and an eminent authority who
was Professor at Oxford and a Fellow of the Royal Society, and who
maintained that _Zoaea_ was a mature and independent form. In the end
taxonomy had to be altered so as to conform with the fact of development,
and the name _Zoaea_ disappeared altogether as that of an independent
genus, persisting only as a convenient term for an important larval stage
in the development of crabs.

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