Transcriber’s Note: Sidenotes are shown enclosed in square brackets,
above the paragraphs to which they apply. Italic text is enclosed in
_underscores_.
DARWINISM
STATED BY DARWIN HIMSELF.
_CHARACTERISTIC PASSAGES
FROM THE WRITINGS OF CHARLES DARWIN._
SELECTED AND ARRANGED
BY
NATHAN SHEPPARD,
AUTHOR OF
“SHUT UP IN PARIS,” EDITOR OF “THE DICKENS READER,” “CHARACTER
READINGS FROM GEORGE ELIOT,” AND “GEORGE ELIOT’S ESSAYS.”
“There is grandeur in this view of life, with its several powers,
having been originally breathed by the Creator into a few forms or
into one; and that, while this planet has gone cycling on according
to the fixed law of gravity, from so simple a beginning endless
forms most beautiful and most wonderful have been and are being
evolved.”--_The Origin of Species_, page 429.
NEW YORK:
D. APPLETON AND COMPANY,
1, 3, AND 5 BOND STREET.
1884.
COPYRIGHT, 1884,
BY D. APPLETON AND COMPANY.
PREFACE.
While these selections can not but be useful to those who are perfectly
familiar with the writings of Darwin, they are designed especially
for those who know little, or nothing, about his line of research and
argument, and yet would like to obtain a general idea of it in a form
which shall be at once authentic, brief, and inexpensive.
This volume contains, of course, only an outline of the contents of
the twelve volumes from which it is compiled, and for which it is by
no means intended as a substitute. It will, on the contrary, we should
hope, create an appetite which can be satisfied only by a careful
reading of the works themselves.
Darwin’s repetitions, necessitated by his method of investigation
and publication, and his unexampled candor in controversy, have been
something of an embarrassment in the classification of these passages;
so that we have been obliged in some instances to sacrifice continuity
to perspicuity. But, as one object of this book is to correct
misrepresentations by giving Darwin’s views in his own language, some
of his own repetitions must be given also, in order to leave no doubt
as to precisely what he said and did not say. It will probably be a
long while before the dispute over the theory that he advocated will
cease, but there is certainly no excuse for a difference of opinion
with regard to the language that he used, and the meaning he attached
to it. That language and that meaning will be found in these pages.
Darwinism stated by its opponents is one thing, Darwinism stated by
Darwin himself will be found to be quite another thing, for, to use his
own exclamation, “great is the power of steady misrepresentation!”
The order followed in the arrangement of these extracts is not that
of the books, but the one naturally suggested by our plan, which is
designed to conduct the reader through the vegetable up to the animal
kingdom, and up from the lowest to the highest animal, man, “the wonder
and glory of the universe.”
The references are to the American edition of Darwin’s works published
by D. Appleton & Co., New York.
It is no part of our purpose to discuss the theory expounded here, but
we can not refrain from joining in the general expression of admiration
for its illustrious expounder. Lord Derby says, “He was one of half
a dozen men of this century who will be remembered a century hence”;
and yet his friends were “more impressed with the dignified simplicity
of his nature than by the great work he had done.” Professor Huxley
compares him to Socrates in wisdom and humility; and there could be no
better authority than Mr. A. R. Wallace for the statement that “there
are none to stand beside him as equals in the whole domain of science.”
He has been extolled, since his death, by a host of religious leaders
in press and pulpit (some of whose utterances will be found on another
page), and we concur with them in the opinion that science never had a
champion whose temper and behavior were more nearly in accord with the
practical injunctions of the Christian religion. Whatever we or any one
may think of Darwin’s scientific theories, no one can gainsay the value
of his personal example, and few can be so prejudiced as to resist the
fascination that will always be felt at the mention of his name.
NEW YORK, _February 1, 1884_.
INTRODUCTORY PASSAGES QUOTED BY DARWIN IN HIS “ORIGIN OF SPECIES.”
“But with regard to the material world, we can at least go so far as
this--we can perceive that events are brought about not by insulated
interpositions of divine power, exerted in each particular case, but by
the establishment of general laws.”--WHEWELL: _Bridgewater Treatise_.
“The only distinct meaning of the word ‘natural’ is _stated_, _fixed_,
or _settled_; since what is natural as much requires and presupposes an
intelligent agent to render it so, i. e., to effect it continually or
at stated times, as what is supernatural or miraculous does to effect
it for once.”--BUTLER: _Analogy of Revealed Religion_.
“To conclude, therefore, let no man out of a weak conceit of sobriety,
or an ill-applied moderation, think or maintain, that a man can
search too far or be too well studied in the book of God’s word, or
in the book of God’s works; divinity or philosophy; but rather let
men endeavor an endless progress or proficience in both.”--BACON:
_Advancement of Learning_.
DARWIN AND HIS THEORIES FROM A RELIGIOUS POINT OF VIEW.
“Surely in such a man lived that true charity which is the very essence
of the true spirit of Christ.”--Canon PROTHERO.
“The moral lesson of his life is perhaps even more valuable than is the
grand discovery which he has stamped on the world’s history.”--_The
Observer_ (London).
“Darwin’s writings may be searched in vain for an irreverent or
unbelieving word.”--_The Church Review._
“The doctrine of evolution with which Darwin’s name would always be
associated lent itself at least as readily to the old promise of God as
to more modern but less complete explanations of the universe.”--Canon
BARRY.
“The fundamental doctrine of the theist is left precisely as it was.
The belief in the great Creator and Ruler of the Universe is, as we
have seen, confessed by the author of these doctrines. The grounds
remain untouched of faith in the personal Deity who is in intimate
relation with individual souls, who is their guide and helper in life,
and who can be trusted in regard to the great hereafter.”--_The Church
Quarterly Review._
“It appears impossible to overrate the gain we have won in the
stupendous majesty of this (Darwin’s) idea of the Creator and
creation.”--_Sunday-School Chronicle._
“It is certain that Mr. Darwin’s books contain a marvelous store of
patiently accumulated and most interesting facts. Those facts seem
to point in the direction of the belief that the Great Spirit of
the Universe has wrought slowly and with infinite patience, through
innumerable ages, rather than by abrupt intervention and by means of
great catastrophes, in the production of the results, in the animate
and inanimate world, which now offer to the student of nature boundless
scope for observation and inquiry.”--_The Christian World._
“Let us see, in the funeral honors paid within these holy precincts to
our greatest naturalist, a happy trophy of the reconciliation between
faith and science.”--_The Guardian._
“That there is some truth in the theory of evolution, however, most
scientists, including those of Christian faith, believe, and Mr. Darwin
certainly has done much to make the facts plain; but no scientific
principle established by him ever has undermined any truth of the
Gospel.”--_The Congregationalist._
“Christian believers are found among the ranks of evolutionists
without apparent prejudice to their faith. Professor Mivart, the
zoölogist; Professor Asa Gray, the botanist; Professor Le Conte and
Professor Winchell, the geologists, may be named as among these.”--_The
Presbyterian._
“In all his simple and noble life Mr. Darwin was influenced by the
profoundly religious conviction that nothing was beneath the earnest
study of man which had been worthy of the mighty hand of God.”--Canon
FARRAR.
“He has not one word to say against religion; ... by-and-by it may be
seen that he has done much to put religious faith as well as scientific
knowledge on a higher plane.”--_Independent._
“A celebrated author and divine has written to me that ‘he has
gradually learned to see that it is just as noble a conception of
the Deity to believe that he created a few original forms capable of
self-development into other and needful forms, as to believe that he
required a fresh act of creation to supply the voids caused by the
action of his laws.’”--_Origin of Species_, page 422.
“I am at the head of a college where to declare against it [evolution]
would perplex my best students. They would ask me which to give up,
science or the Bible.... It is but the evolution of Genesis when each
‘brings forth after its kind.’ Science tells the same story. But what
is the limit of the fixedness of the law? I believe that the evolution
of new species is a question in science, and not of religion. It should
be left to scientific men.”--President MCCOSH.
CONTENTS.
I.
PAGE
THE MOVEMENTS AND HABITS OF PLANTS.
The Movement of Plants in Relation to their Wants 2
The Power of Movement in Animal and Plant compared 4
Advantages of Cross-Fertilization 6
Potency of the Sexual Elements in Plants 6
Experiments in Crossing 8
The Struggle for Existence among Seeds 9
Practical Application of these Views 9
Marriages of First Cousins 11
Development of the Two Sexes in Plants 12
Why the Sexes have been reseparated 14
Comparative Fertility of Male and Female Plants 15
Effect of Climate on Reproduction 16
Causes of Sterility among Plants 17
An “Ideal Type” or Inevitable Modification 18
Special Adaptations to a Changing Purpose 19
An Illustration 21
As interesting on the Theory of Development as on that of Direct
Interposition 22
The Sleep of the Plants 24
Self-Protection during Sleep 25
Influence of Light upon Plants 28
Influence of Gravitation upon Plants 29
The Power of Digestion in Plants 31
Diverse Means by which Plants gain their Subsistence 34
How a Plant preys upon Animals 35
II.
THE PART PLAYED BY WORMS IN THE HISTORY OF THIS PLANET.
They preserve Valuable Ruins 42
They prepare the Ground for Seed 43
Intelligence of Worms 45
III.
THE LAWS OF VARIABILITY WITH RESPECT TO ANIMALS AND PLANTS.
Inherited Effect of Changed Habits 48
Effects of the Use and Disuse of Parts 50
Vague Origin of our Domestic Animals 52
Descent of the Domestic Pigeon 53
Origin of the Dog 55
Origin of the Horse 57
Causes of Modifications in the Horse 58
“Making the Works of God a mere Mockery” 59
Variability of Cultivated Plants 61
Savage Wisdom in the Cultivation of Plants 62
Unknown Laws of Inheritance 64
Laws of Inheritance that are fairly well established 66
Inherited Peculiarities in Man 67
Inherited Diseases 68
Causes of Non-Inheritance 69
Steps by which Domestic Races have been produced 71
Unconscious Selection 73
Adaptation of Animals to the Fancies of Man 74
Doubtful Species 75
Species an Arbitrary Term 77
The True Plan of Creation 79
IV.
THE STRUGGLE FOR EXISTENCE.
Death inevitable in the Fight for Life 82
“Inexplicable on the Theory of Creation” 84
Obscure Checks to Increase 85
Climate as a Check to Increase 86
Influence of Insects in the Struggle for Existence 88
No such Thing as Change in the Result of the Struggle 90
V.
NATURAL SELECTION; OR, THE SURVIVAL OF THE FITTEST.
An Invented Hypothesis 93
How far the Theory may be extended 94
Is there any Limit to what Selection can effect? 96
Has Organization advanced? 97
A Higher Workmanship than Man’s 99
Why Habits and Structure are not in Agreement 102
No Modification in one Species designed for the Good of Another 103
Illustrations of the Action of Natural Selection 106
Divergence of Character 108
Evolution of the Human Eye 110
VI.
GEOGRAPHICAL DISTRIBUTION OF ORGANIC BEINGS.
Isolated Continents never were united 115
Means of Dispersal 116
These Means of Transport not accidental 118
Dispersal during the Glacial Period 119
The Theory of Creation inadequate 122
Causes of a Glacial Climate 123
Difficulties not yet removed 124
Identity of the Species of Islands with those of the Mainland
explained only by this Theory 125
VII.
EVIDENCE OF THE DESCENT OF MAN FROM SOME LOWER FORM.
Points of Correspondence between Man and the other Animals 129
The facts of Embryology and the Theory of Development 131
Two Principles that explain the Facts 134
Embryology against Abrupt Changes 135
Rudimentary Organs only to be explained on the Theory of
Development 137
“No other Explanation has ever been given” 139
Unity of Type explained by Relationship 140
Inexplicable on the Ordinary View of Creation 142
Descent with Modification the only Explanation 143
The History of Life on the Theory of Descent with Modification 144
Letters retained in the Spelling but Useless in Pronunciation 146
Man’s Deficiency in Tail 147
Points of Resemblance between Man and Monkey 149
Variability of Man 152
Causes of Variability in Domesticated Man 153
Action of Changed Conditions 155
The Inherited Effects of the Increased and Diminished Use of
Parts 156
Reversion as a Factor in the Development of Man 158
Reversion in the Human Family 160
Prepotence in the Transmission of Character 162
Natural Selection in the Development of Man 163
How Man became upright 165
The Brain enlarges as the Mental Faculties develop 167
Nakedness of the Skin 169
Is Man the most helpless of the Animals? 171
VIII.
MENTAL POWERS OF MAN AND THE LOWER ANIMALS COMPARED.
Fundamental Intuitions the same in Man and the other Animals 175
Man and the Lower Animals excited by the same Emotions 177
All Animals possess some Power of Reasoning 179
The Power of Association in Dog and Savage 181
The Lower Animals progress in Intelligence 182
The Power of Abstraction 183
The Evolution of Language 185
Development of Languages and Species compared 188
The Sense of Beauty 191
Development of the Ear for Music 192
IX.
DEVELOPMENT OF THE MORAL SENSE.
From the Social Instincts to the Moral Sense 195
Human Sympathy among Animals 197
The Love of Approbation 199
Fellow-Feeling for our Fellow-Animals 200
Development of the Golden Rule 201
Regret peculiar to Man, and why 202
Remorse explained 204
Development of Self-Control 205
Variability of Conscience 207
Progress not an Invariable Rule 209
All Civilized Nations are the Descendants of Barbarians 210
“The Ennobling Belief in God” 213
X.
THE GENEALOGY OF MAN.
Man a Sub-Order 218
The Birthplace of Man 221
Origin of the Vertebrata 224
From no Bone to Backbone 226
Does Mankind consist of Several Species? 228
The Races graduate into each other 229
Was the First Man a Speaking Animal? 231
The Theory of a Single Pair 231
Civilized out of Existence 233
XI.
SEXUAL SELECTION AS AN AGENCY TO ACCOUNT FOR THE DIFFERENCES
BETWEEN THE RACES OF MAN.
Struggle of the Males for the Possession of the Females 236
Courtship among the Lower Animals 237
Why the Male plays the more Active Part in Courting 239
Transmission of Sexual Characteristics 240
An Objection answered 242
Difference between the Sexes created by Sexual Selection 243
How Woman could be made to reach the Standard of Man 246
“Characteristic Selfishness of Man” 247
No Universal Standard of Beauty among Mankind 248
Development of the Beard 249
Development of the Marriage-Tie 250
Unnatural Selection in Marriage 252
Modifying Influences in Both Sexes 254
“Grounds that will never be shaken” 256
XII.
THE EXPRESSION OF THE EMOTIONS IN MAN AND OTHER ANIMALS.
The Principle of Associated Habit 258
The Principle of Antithesis 261
Origin of the Principle of Antithesis 263
The Principle of the Action of the Excited Nervous System on the
Body 265
XIII.
MEANS OF THE EXPRESSION OF THE EMOTIONS.
Vocal Organs 268
Erection of the Hair 269
Erection of the Ears 270
A Startled Horse 271
Monkey-Shines 271
Weeping of Man and Brute 272
The Grief-Muscles 275
Voluntary Power over the Grief-Muscles 276
“Down in the Mouth” 278
Laughter 279
Expression of the Devout Emotions 282
Frowning 284
Pouting 285
Decision at the Mouth 287
Anger 287
Sneering 288
Disgust 289
Shrugging the Shoulders 290
Blushing 291
Blushing not necessarily an Expression of Guilt 293
Blushing accounted for 294
A New Argument for a Single Parent-Stock 296
XIV.
THE PROVISIONAL HYPOTHESIS OF PANGENESIS.
Functional Independence of the Units of the Body 299
Necessary Assumptions 302
Two Objections answered 305
Effect of Morbid Action 306
Transmission limited 307
XV.
OBJECTIONS TO THE THEORY OF DESCENT WITH MODIFICATION CONSIDERED.
Misrepresentations corrected 310
Lapse of Time and Extent of Area 311
Why the Higher Forms have not supplanted the Lower 313
The Amount of Life must have a Limit 316
The Broken Branches of the Tree of Life 317
Why we do not find Transitional Forms 319
How could the Transitional Form have subsisted? 322
Why Nature takes no Sudden Leaps 323
Imperfect Contrivances of Nature accounted for 324
Instincts as a Difficulty 325
Some Instincts acquired and some lost 327
Innumerable Links necessarily lost 329
Plenty of Time for the Necessary Gradations 331
Wide Intervals of Time between the Geological Formations 334
Sudden Appearance of Groups of Allied Species 336
How little we know of Former Inhabitants of the World 337
The Extinction of Species involved in Mystery 338
Dead Links between Living Species 340
Living Descendants of Fossil Species 342
Unnecessary to explain the Cause of each Individual Difference 343
“Face to Face with an Insoluble Difficulty” 344
Why distasteful? 346
“Accords better with what we know of the Creator’s Laws” 347
The Grandeur of this View of Life 348
Not incompatible with the Belief in Immortality 349
DARWINISM
STATED BY DARWIN HIMSELF.
I.
THE MOVEMENTS AND HABITS OF PLANTS.
[The Power
of Movement
in Plants,
page 1.]
The most widely prevalent movement is essentially of the same nature
as that of the stem of a climbing plant, which bends successively to
all points of the compass, so that the tip revolves. This movement has
been called by Sachs “revolving nutation”; but we have found it much
more convenient to use the terms _circumnutation_ and _circumnutate_.
As we shall have to say much about this movement, it will be useful
here briefly to describe its nature. If we observe a circumnutating
stem, which happens at the time to be bent, we will say toward the
north, it will be found gradually to bend more and more easterly, until
it faces the east; and so onward to the south, then to the west, and
back again to the north. If the movement had been quite regular, the
apex would have described a circle, or rather, as the stem is always
growing upward, a circular spiral. But it generally describes irregular
elliptical or oval figures; for the apex, after pointing in any one
direction, commonly moves back to the opposite side, not, however,
returning along the same line. Afterward other irregular ellipses or
ovals are successively described, with their longer axes directed to
different points of the compass. While describing such figures, the
apex often travels in a zigzag line, or makes small subordinate loops
or triangles. In the case of leaves the ellipses are generally narrow.
[Page 3.]
Even the stems of seedlings before they have broken through the ground,
as well as their buried radicles, circumnutate, as far as the pressure
of the surrounding earth permits. In this universally present movement
we have the basis or groundwork for the acquirement, according to the
requirements of the plant, of the most diversified movements.
THE MOVEMENT OF PLANTS IN RELATION TO THEIR WANTS.
[The Movements
and Habits
of Climbing
Plants,
page 202.]
The most interesting point in the natural history of climbing plants
is the various kinds of movement which they display in manifest
relation to their wants. The most different organs--stems, branches,
flower-peduncles, petioles, mid-ribs of the leaf and leaflets, and
apparently aërial roots--all possess this power.
1. The first action of a tendril is to place itself in a proper
position. For instance, the tendril of _Cobæa_ first rises vertically
up, with its branches divergent and with the terminal hooks turned
outward; the young shoot at the extremity of the stem is at the same
time bent to one side, so as to be out of the way. The young leaves of
clematis, on the other hand, prepare for action by temporarily curving
themselves downward, so as to serve as grapnels.
2. If a twining plant or a tendril gets by any accident into an
inclined position, it soon bends upward, though secluded from the
light. The guiding stimulus no doubt is the attraction of gravity, as
Andrew Knight showed to be the case with germinating plants. If a shoot
of any ordinary plant be placed in an inclined position in a glass of
water in the dark, the extremity will, in a few hours, bend upward;
and, if the position of the shoot be then reversed, the downward-bent
shoot reverses its curvature; but if the stolon of a strawberry, which
has no tendency to grow upward, be thus treated, it will curve downward
in the direction of, instead of in opposition to, the force of gravity.
As with the strawberry, so it is generally with the twining shoots of
the _Hibbertia dentata_, which climbs laterally from bush to bush; for
these shoots, if placed in a position inclined downward, show little
and sometimes no tendency to curve upward.
3. Climbing plants, like other plants, bend toward the light by a
movement closely analogous to the incurvation which causes them to
revolve, so that their revolving movement is often accelerated or
retarded in traveling to or from the light. On the other hand, in a few
instances tendrils bend toward the dark.
4. We have the spontaneous revolving movement which is independent of
any outward stimulus, but is contingent on the youth of the part, and
on vigorous health; and this again, of course, depends on a proper
temperature and other favorable conditions of life.
5. Tendrils, whatever their homological nature may be, and the petioles
or tips of the leaves of leaf-climbers, and apparently certain roots,
all have the power of movement when touched, and bend quickly toward
the touched side. Extremely slight pressure often suffices. If the
pressure be not permanent, the part in question straightens itself and
is again ready to bend on being touched.
6. Tendrils, soon after clasping a support, but not after a mere
temporary curvature, contract spirally. If they have not come into
contact with any object, they ultimately contract spirally, after
ceasing to revolve; but in this case the movement is useless, and
occurs only after a considerable lapse of time.
With respect to the means by which these various movements are
effected, there can be little doubt, from the researches of Sachs and
H. de Vries, that they are due to unequal growth; but, from the reasons
already assigned, I can not believe that this explanation applies to
the rapid movements from a delicate touch.
Finally, climbing plants are sufficiently numerous to form a
conspicuous feature in the vegetable kingdom, more especially in
tropical forests. America, which so abounds with arboreal animals,
as Mr. Bates remarks, likewise abounds, according to Mohl and Palm,
with climbing plants; and, of the tendril-bearing plants examined by
me, the highest developed kinds are natives of this grand continent,
namely, the several species of _Bignonia_, _Eccremocarpus_, _Cobæa_,
and _Ampelopsis_. But even in the thickets of our temperate regions the
number of climbing species and individuals is considerable, as will be
found by counting them.
THE POWER OF MOVEMENT IN ANIMAL AND PLANT COMPARED.
[Page 206.]
It has often been vaguely asserted that plants are distinguished from
animals by not having the power of movement. It should rather be said
that plants acquire and display this power only when it is of some
advantage to them; this being of comparatively rare occurrence, as
they are affixed to the ground, and food is brought to them by the air
and rain. We see how high in the scale of organization a plant may
rise, when we look at one of the more perfect tendril-bearers. It
first places its tendrils ready for action, as a polypus places its
tentacula. If the tendril be displaced, it is acted on by the force
of gravity and rights itself. It is acted on by the light, and bends
toward or from it, or disregards it, whichever maybe most advantageous.
During several days the tendrils or internodes, or both, spontaneously
revolve with a steady motion. The tendril strikes some object, and
quickly curls round and firmly grasps it. In the course of some hours
it contracts into a spire, dragging up the stem, and forming an
excellent spring. All movements now cease. By growth the tissues soon
become wonderfully strong and durable. The tendril has done its work,
and has done it in an admirable manner.
* * * * *
[The Power
of Movement
in Plants,
page 571.]
It is impossible not to be struck with the resemblance between the
foregoing movements of plants and many of the actions performed
unconsciously by the lower animals. With plants an astonishingly
small stimulus suffices; and even with allied plants one may be
highly sensitive to the slightest continued pressure, and another
highly sensitive to a slight momentary touch. The habit of moving at
certain periods is inherited both by plants and animals; and several
other points of similitude have been specified. But the most striking
resemblance is the localization of their sensitiveness, and the
transmission of an influence from the excited part to another which
consequently moves. Yet plants do not, of course, possess nerves or
a central nervous system; and we may infer that with animals such
structures serve only for the more perfect transmission of impressions,
and for the more complete intercommunication of the several parts.
ADVANTAGES OF CROSS-FERTILIZATION.
[The Effects
of Cross
and Self
Fertilization
in the
Vegetable
Kingdom,
page 443.]
There are two important conclusions which may be deduced from my
observations: 1. That the advantages of cross-fertilization do not
follow from some mysterious virtue in the mere union of two distinct
individuals, but from such individuals having been subjected during
previous generations to different conditions, or to their having
varied in a manner commonly called spontaneous, so that in either case
their sexual elements have been in some degree differentiated; and, 2.
That the injury from self-fertilization follows from the want of such
differentiation in the sexual elements. These two propositions are
fully established by my experiments. Thus, when plants of the _Ipomœa_
and of the _Mimulus_, which had been self-fertilized for the seven
previous generations, and had been kept all the time under the same
conditions, were intercrossed one with another, the offspring did not
profit in the least by the cross.
* * * * *
[Page 451.]
The curious cases of plants which can fertilize and be fertilized by
any other individual of the same species, but are altogether sterile
with their own pollen, become intelligible, if the view here propounded
is correct, namely, that the individuals of the same species growing in
a state of nature near together have not really been subjected during
several previous generations to quite the same conditions.
POTENCY OF THE SEXUAL ELEMENTS IN PLANTS.
[Page 446.]
It is obvious that the exposure of two sets of plants during several
generations to different conditions can lead to no beneficial results,
as far as crossing is concerned, unless their sexual elements are
thus affected. That every organism is acted on to a certain extent by
a change in its environment will not, I presume, be disputed. It is
hardly necessary to advance evidence on this head; we can perceive the
difference between individual plants of the same species which have
grown in somewhat more shady or sunny, dry or damp places. Plants which
have been propagated for some generations under different climates or
at different seasons of the year transmit different constitutions to
their seedlings. Under such circumstances, the chemical constitution
of their fluids and the nature of their tissues are often modified.
Many other such facts could be adduced. In short, every alteration in
the function of a part is probably connected with some corresponding,
though often quite imperceptible, change in structure or composition.
Whatever affects an organism in any way, likewise tends to act on its
sexual elements. We see this in the inheritance of newly acquired
modifications, such as those from the increased use or disuse of
a part, and even from mutilations if followed by disease. We have
abundant evidence how susceptible the reproductive system is to changed
conditions, in the many instances of animals rendered sterile by
confinement; so that they will not unite, or, if they unite, do not
produce offspring, though the confinement may be far from close; and
of plants rendered sterile by cultivation. But hardly any cases afford
more striking evidence how powerfully a change in the conditions of
life acts on the sexual elements than those already given, of plants
which are completely self-sterile in one country, and, when brought
to another, yield, even in the first generation, a fair supply of
self-fertilized seeds.
But it may be said, granting that changed conditions act on the sexual
elements, How can two or more plants growing close together, either in
their native country or in a garden, be differently acted on, inasmuch
as they appear to be exposed to exactly the same conditions?
EXPERIMENTS IN CROSSING.
[Page 447.]
In my experiments with _Digitalis purpurea_, some flowers on a wild
plant were self-fertilized, and others were crossed with pollen from
another plant growing within two or three feet distance. The crossed
and self-fertilized plants raised from the seeds thus obtained
produced flower-stems in number as 100 to 47, and in average height
as 100 to 70. Therefore, the cross between these two plants was
highly beneficial; but how could their sexual elements have been
differentiated by exposure to different conditions? If the progenitors
of the two plants had lived on the same spot during the last score
of generations, and had never been crossed with any plant beyond the
distance of a few feet, in all probability their offspring would
have been reduced to the same state as some of the plants in my
experiments--such as the intercrossed plants of the ninth generation
of _Ipomœa_, or the self-fertilized plants of the eighth generation of
_Mimulus_, or the offspring from flowers on the same plant; and in this
case a cross between the two plants of _Digitalis_ would have done no
good. But seeds are often widely dispersed by natural means, and one
of the above two plants, or one of their ancestors, may have come from
a distance, from a more shady or sunny, dry or moist place, or from
a different kind of soil containing other organic seeds or inorganic
matter.
THE STRUGGLE FOR EXISTENCE AMONG SEEDS.
[Page 449.]
Seeds often lie dormant for several years in the ground, and germinate
when brought near the surface by any means, as by burrowing animals.
They would probably be affected by the mere circumstance of having
long lain dormant; for gardeners believe that the production of double
flowers, and of fruit, is thus influenced. Seeds, moreover, which were
matured during different seasons will have been subjected during the
whole course of their development to different degrees of heat and
moisture.
It has been shown that pollen is often carried by insects to a
considerable distance from plant to plant. Therefore, one of the
parents or ancestors of our two plants of _Digitalis_ may have been
crossed by a distant plant growing under somewhat different conditions.
Plants thus crossed often produce an unusually large number of seeds;
a striking instance of this fact is afforded by the _Bignonia_, which
was fertilized by Fritz Müller with pollen from some adjoining plants
and set hardly any seed, but, when fertilized with pollen from a
distant plant, was highly fertile. Seedlings from a cross of this kind
grow with great vigor, and transmit their vigor to their descendants.
These, therefore, in the struggle for life, will generally beat and
exterminate the seedlings from plants which have long grown near
together under the same conditions, and will thus tend to spread.
PRACTICAL APPLICATION OF THESE VIEWS.
[Page 458.]
Under a practical point of view, agriculturists and horticulturists
may learn something from the conclusions at which we have arrived.
Firstly, we see that the injury from the close breeding of animals
and from the self-fertilization of plants does not necessarily
depend on any tendency to disease or weakness of constitution common
to the related parents, and only indirectly on their relationship,
in so far as they are apt to resemble each other in all respects,
including their sexual nature. And, secondly, that the advantages
of cross-fertilization depend on the sexual elements of the parents
having become in some degree differentiated by the exposure of their
progenitors to different conditions, or from their having intercrossed
with individuals thus exposed; or, lastly, from what we call in
our ignorance spontaneous variation. He therefore who wishes to
pair closely related animals ought to keep them under conditions as
different as possible.
* * * * *
[Page 459.]
As some kinds of plants suffer much more from self-fertilization than
do others, so it probably is with animals from too close interbreeding.
The effects of close interbreeding on animals, judging again from
plants, would be deterioration in general vigor, including fertility,
with no necessary loss of excellence of form; and this seems to be the
usual result.
It is a common practice with horticulturists to obtain seeds from
another place having a very different soil, so as to avoid raising
plants for a long succession of generations under the same conditions;
but, with all the species which freely intercross by the aid of insects
or the wind, it would be an incomparably better plan to obtain seeds
of the required variety, which had been raised for some generations
under as different conditions as possible, and sow them in alternate
rows with seeds matured in the old garden. The two stocks would then
intercross, with a thorough blending of their whole organizations, and
with no loss of purity to the variety; and this would yield far more
favorable results than a mere exchange of seeds. We have seen in my
experiments how wonderfully the offspring profited in height, weight,
hardiness, and fertility, by crosses of this kind. For instance,
plants of _Ipomœa_ thus crossed were to the intercrossed plants of
the same stock, with which they grew in competition, as 100 to 78 in
height, and as 100 to 51 in fertility; and plants of _Eschscholtzia_
similarly compared were as 100 to 45 in fertility. In comparison
with self-fertilized plants the results are still more striking;
thus cabbages derived from a cross with a fresh stock were to the
self-fertilized as 100 to 22 in weight.
Florists may learn, from the four cases which have been fully
described, that they have the power of fixing each fleeting variety
of color, if they will fertilize the flowers of the desired kind with
their own pollen for half a dozen generations, and grow the seedlings
under the same conditions. But a cross with any other individual of the
same variety must be carefully prevented, as each has its own peculiar
constitution. After a dozen generations of self-fertilization, it is
probable that the new variety would remain constant even if grown
under somewhat different conditions; and there would no longer be any
necessity to guard against intercrosses between the individuals of the
same variety.
MARRIAGES OF FIRST COUSINS.
[Page 460.]
With respect to mankind, my son George has endeavored to discover by
a statistical investigation whether the marriages of first cousins
are at all injurious, although this is a degree of relationship which
would not be objected to in our domestic animals; and he has come to
the conclusion from his own researches, and those of Dr. Mitchell,
that the evidence as to any evil thus caused is conflicting, but on
the whole points to its being very small. From the facts given in this
volume we may infer that with mankind the marriages of nearly related
persons, some of whose parents and ancestors had lived under very
different conditions, would be much less injurious than that of persons
who had always lived in the same place and followed the same habits of
life. Nor can I see reason to doubt that the widely different habits of
life of men and women in civilized nations, especially among the upper
classes, would tend to counterbalance any evil from marriages between
healthy and somewhat closely related persons.
DEVELOPMENT OF THE TWO SEXES IN PLANTS.
[Page 461.]
Under a theoretical point of view it is some gain to science to know
that numberless structures in hermaphrodite plants, and probably
in hermaphrodite animals, are special adaptations for securing an
occasional cross between two individuals; and that the advantages from
such a cross depend altogether on the beings which are united, or their
progenitors, having had their sexual elements somewhat differentiated,
so that the embryo is benefited in the same manner as is a mature plant
or animal by a slight change in its conditions of life, although in a
much higher degree.
Another and more important result may be deduced from my observations.
Eggs and seeds are highly serviceable as a means of dissemination,
but we now know that fertile eggs can be produced without the aid of
the male. There are also many other methods by which organisms can be
propagated asexually. Why then have the two sexes been developed, and
why do males exist which can not themselves produce offspring? The
answer lies, as I can hardly doubt, in the great good which is derived
from the fusion of two somewhat differentiated individuals; and with
the exception of the lowest organisms this is possible only by means
of the sexual elements, these consisting of cells separated from the
body, containing the germs of every part, and capable of being fused
completely together.
It has been shown in the present volume that the offspring from the
union of two distinct individuals, especially if their progenitors
have been subjected to very different conditions, have an immense
advantage in height, weight, constitutional vigor and fertility over
the self-fertilized offspring from one of the same parents. And this
fact is amply sufficient to account for the development of the sexual
elements, that is, for the genesis of the two sexes.
It is a different question why the two sexes are sometimes combined
in the same individual, and are sometimes separated. As with many of
the lowest plants and animals the conjugation of two individuals,
which are either quite similar or in some degree different is a common
phenomenon, it seems probable, as remarked in the last chapter, that
the sexes were primordially separate. The individual which receives
the contents of the other, may be called the female; and the other,
which is often smaller and more locomotive, may be called the male;
though these sexual names ought hardly to be applied as long as the
whole contents of the two forms are blended into one. The object
gained by the two sexes becoming united in the same hermaphrodite form
probably is to allow of occasional or frequent self-fertilization,
so as to insure the propagation of the species, more especially in
the case of organisms affixed for life to the same spot. There does
not seem to be any great difficulty in understanding how an organism,
formed by the conjugation of two individuals which represented the two
incipient sexes, might have given rise by budding first to a monœcious
and then to an hermaphrodite form; and in the case of animals even
without budding to an hermaphrodite form, for the bilateral structure
of animals perhaps indicates that they were aboriginally formed by the
fusion of two individuals.
WHY THE SEXES HAVE BEEN RESEPARATED.
[Page 463.]
It is a more difficult problem why some plants, and apparently all
the higher animals, after becoming hermaphrodites, have since had
their sexes reseparated. This separation has been attributed by
some naturalists to the advantages which follow from a division of
physiological labor. The principle is intelligible when the same organ
has to perform at the same time diverse functions; but it is not
obvious why the male and female glands, when placed in different parts
of the same compound or simple individual, should not perform their
functions equally well as when placed in two distinct individuals. In
some instances the sexes may have been reseparated for the sake of
preventing too frequent self-fertilization; but this explanation does
not seem probable, as the same end might have been gained by other and
simpler means, for instance, dichogamy. It may be that the production
of the male and female reproductive elements and the maturation of
the ovules was too great a strain and expenditure of vital force for
a single individual to withstand, if endowed with a highly complex
organization; and that at the same time there was no need for all the
individuals to produce young, and consequently that no injury, on the
contrary, good, resulted from half of them, or the males, failing to
produce offspring.
COMPARATIVE FERTILITY OF MALE AND FEMALE PLANTS.
[The Different
Forms of
Flowers,
page 290.]
Thirteen bushes (of the spindle-tree) growing near one another in a
hedge consisted of eight females quite destitute of pollen, and of five
hermaphrodites with well-developed anthers. In the autumn the eight
females were well covered with fruit, excepting one which bore only a
moderate number. Of the five hermaphrodites, one bore a dozen or two
fruits, and the remaining four bushes several dozen; but their number
was as nothing compared with those on the female bushes, for a single
branch, between two and three feet in length, from one of the latter,
yielded more than any one of the hermaphrodite bushes. The difference
in the amount of fruit produced by the two sets of bushes is all the
more striking, as from the sketches above given it is obvious that the
stigmas of the polleniferous flowers can hardly fail to receive their
own pollen; while the fertilization of the female flowers depends on
pollen being brought to them by flies and the smaller _Hymenoptera_,
which are far from being such efficient carriers as bees.
I now determined to observe more carefully during successive seasons
some bushes growing in another place about a mile distant. As the
female bushes were so highly productive, I marked only two of them with
the letters A and B, and five polleniferous bushes with the letters C
to G. I may premise that the year 1865 was highly favorable for the
fruiting of all the bushes, especially for the polleniferous ones, some
of which were quite barren, except under such favorable conditions.
The season of 1864 was unfavorable. In 1863 the female A produced “some
fruit”; in 1864 only nine; and in 1865 ninety-seven fruit. The female
B in 1863 was “covered with fruit”; in 1864 it bore twenty-eight; and
in 1865 “innumerable very fine fruits.” I may add that three other
female trees growing close by were observed, but only during 1863, and
they then bore abundantly. With respect to the polleniferous bushes,
the one marked C did not bear a single fruit during the years 1863
and 1864, but during 1865 it produced no less than ninety-two fruit,
which, however, were very poor. I selected one of the finest branches
with fifteen fruit, and these contained twenty seeds, or on an average
1·33 per fruit. I then took by hazard fifteen fruit from an adjoining
female bush, and these contained forty-three seeds; that is, more than
twice as many, or on an average 2·86 per fruit. Many of the fruits
from the female bushes included four seeds, and only one had a single
seed; whereas, not one fruit from the polleniferous bushes contained
four seeds. Moreover, when the two lots of seeds were compared, it was
manifest that those from the female bushes were the larger. The second
polleniferous bush, D, bore in 1863 about two dozen fruit, in 1864 only
three very poor fruit, each containing a single seed; and in 1865,
twenty equally poor fruit. Lastly, the three polleniferous bushes, E,
F, and G, did not produce a single fruit during the three years 1863,
1864, and 1865.
EFFECT OF CLIMATE ON REPRODUCTION.
[Page 293.]
A tendency to the separation of the sexes in the cultivated strawberry
seems to be much more strongly marked in the United States than in
Europe; and this appears to be the result of the direct action of
climate on the reproductive organs. In the best account which I have
seen, it is stated that many of the varieties in the United States
consist of three forms, namely, females, which produce a heavy crop
of fruit; of hermaphrodites, which “seldom produce other than a very
scanty crop of inferior and imperfect berries”; and of males, which
produce none. The most skillful cultivators plant “seven rows of female
plants, then one row of hermaphrodites, and so on throughout the
field.” The males bear large, the hermaphrodites mid-sized, and the
females small flowers. The latter plants produce few runners, while the
two other forms produce many; consequently, as has been observed both
in England and in the United States, the polleniferous forms increase
rapidly and tend to supplant the females. We may therefore infer that
much more vital force is expended in the production of ovules and fruit
than in the production of pollen.
CAUSES OF STERILITY AMONG PLANTS.
[The Different
Forms of
Flower,
page 345.]
If the sexual elements belonging to the same form are united, the
union is an illegitimate one, and more or less sterile. With dimorphic
species two illegitimate unions, and with trimorphic species twelve are
possible. There is reason to believe that the sterility of these unions
has not been specially acquired, but follows as an incidental result
from the sexual elements of the two or three forms having been adapted
to act on one another in a particular manner, so that any other kind
of union is inefficient, like that between distinct species. Another
and still more remarkable incidental result is that the seedlings from
an illegitimate union are often dwarfed and more or less completely
barren, like hybrids from the union of two widely distinct species.
AN “IDEAL TYPE” OR INEVITABLE MODIFICATION?
[Fertilization
of Orchids
by Insects,
page 245.]
It is interesting to look at one of the magnificent exotic species
(orchids), or, indeed, at one of our humblest forms, and observe
how profoundly it has been modified, as compared with all ordinary
flowers--with its great labellum, formed of one petal and two petaloid
stamens; with its singular pollen-masses, hereafter to be referred to;
with its column formed of seven cohering organs, of which three alone
perform their proper function, namely, one anther and two generally
confluent stigmas; with the third stigma modified into the rostellum
and incapable of being fertilized; and with three of the anthers no
longer functionally active, but serving either to protect the pollen
of the fertile anther or to strengthen the column, or existing as mere
rudiments, or entirely suppressed. What an amount of modification,
cohesion, abortion, and change of function do we here see! Yet hidden
in that column, with its surrounding petals and sepals, we know that
there are fifteen groups of vessels, arranged three within three, in
alternate order, which probably have been preserved to the present
time from being developed at a very early period of growth, before the
shape or existence of any part of the flower is of importance for the
well-being of the plant.