THE EFFECTS OF CHANGED CONDITIONS: ADAPTATION
In the attempt to conceive a process by which Evolution may have come
about, the first phenomenon to be recognized and accounted for is
specific difference. With that recognition the outline of the problem is
defined. The second prerogative fact is adaptation. Forms of life are
_on the whole_ divided into species, and these species _on the whole_
are adapted and fit the places in which they live. To many students of
Evolution, adaptation has proved so much more interesting and impressive
than specific diversity that they have preferred it to the first place
in their considerations.
Whether this is, as I believe, an inversion of the logical order or
not, there is one most serious practical objection to such preference,
that whereas specific diversity is a subject which can be investigated
both by the study of variation and by the analytical apparatus which
modern genetic science has developed, we have no very effectual means of
directly attacking the problems of Adaptation.
The absence of any definite progress in genetics in the last century was
in great measure due to the exclusive prominence given to the problem
of Adaptation. Almost all debates on heredity centered in that part of
the subject. No one disputes that the adaptation of organisms to their
surroundings is one of the great problems of nature, but it is not the
primary problem of descent. Moreover, until the normal and undisturbed
course of descent under uniform conditions is ascertained with some
exactness, it is useless to attempt a survey of the consequences of
external interference; nor as a rule can it be even possible to decide
with much confidence whether such interferences have or have not
definite consequences. Those, for example, who debated with enthusiasm
whether acquired characters are or are not transmitted were constantly
engaged in discussing occurrences which we now know to be ordinary
features of descent under uniform conditions, and the origin of
variations which were certainly not caused directly by circumstances at
all. In the absence of any factorial analysis, or of any conception of
what factorial composition means and implies, no one knew what varieties
might be expected from given parents. The appearance of any recessive
variety was claimed as a consequence of some treatment which might have
been applied to the parents. There was no possible standard of evidence
or means of controlling it, and thus the discussion was singularly
unfruitful. Before we can tell how the course of descent has departed
from the normal, we must know what the normal would have been if we
had let alone. We are still far from having such knowledge in adequate
measure, but it does now exist in some degree, and we are steadily
approaching a position from which we shall be able to form fairly
sound estimates of the true significance of evidence for or against
the proposition that environmental treatment can produce positive
disturbances in the physiological course of descent.
Thus described, the field for consideration is very wide. Though the
effects of changed conditions were especially studied in the hope of
solving the problem of adaptation by direct observation, that, as all
are now agreed, is but a part of a more general question. We must ask
not only do changed conditions produce an _adaptative_ response on the
part of the offspring, but whether they produce any response on the
part of the offspring at all. It is not in doubt that by violent means,
such as starvation or poisoning of the reproductive cells, effects of a
kind, stunting and deformity for instance, can be made evident, just as
similar effects may follow similar treatment during embryonic or larval
life. Apart from interferences of this class, are there any that may be
reasonably invoked as modifying the course of inheritance?
No epitome of the older evidence for the inheritance of adaptative
changes is here required. That has often been collected, especially
by Weismann, who exposed its weaknesses so thoroughly as to carry
conviction to most minds, and showed that whether the phenomenon
occurs or not, no one can yet prove that it does. Belief in these
transmissions, after being almost universally held, was with singular
unanimity abandoned. This change in opinion, though doing credit to the
faith of the scientific community in evidential reasoning, is the more
remarkable inasmuch as the strength of the idea was not derived from the
minute amounts of supposed facts now demolished. On the contrary, it was
really an instinctive deduction from a wide superficial acquaintance
with the properties of animals and plants. They _can_ accommodate
themselves to circumstances. They _do_ make responses sometimes
marvellously appropriate to demands for which they can scarcely have
been prepared. What more natural than to suppose that the permanent
adaptations have been achieved by inherited summation of such responses?
No one had actually been driven to believe in the inheritance of
adaptative changes because bitches which had been docked had been known
to give birth to tailless puppies, or because certain wheat in Norway
was alleged to have become acclimatized in a few generations. Evidence
of this kind was collected and produced rather as an ornamental appendix
to a proposition already accepted, and held to be plainly demonstrated
by the facts of nature. Looked at indeed in that preliminary and
uncritical way, the case is simply overwhelming. Those who desire to see
how strong it is should turn to Samuel Butler's _Life and Habit_, and
even if in reading they reiterate to themselves that no experimental
evidence exists in support of the propositions advanced, the misgiving
that none the less they may be true is likely to remain. Making every
deduction for the fact that the wonders of adaptation have been grossly
exaggerated, and that marvels of fitness and correspondence between
means and ends have grown out of mere anthropomorphic speculations,
there is much more left to be accounted for than can at all comfortably
be accepted as the product of happy accidents. So oppressive are these
difficulties that we can scarcely blame those who imagine that the study
of heredity is primarily directed to the problem of the transmission of
acquired characters, a preconception still almost universal among the
laity.
But since the belief in transmission of acquired adaptations arose
from preconception rather than from evidence, it is worth observing
that, rightly considered, the probability should surely be the other
way. For the adaptations relate to every variety of exigency. To supply
themselves with food, to find it, to seize and digest it, to protect
themselves from predatory enemies whether by offence or defence, to
counter-balance the changes of temperature, or pressure, to provide for
mechanical strains, to obtain immunity from poison and from invading
organisms, to bring the sexual elements into contact, to ensure the
distribution of the type; all these and many more are accomplished by
organisms in a thousand most diverse and alternative methods. Those are
the things that are hard to imagine as produced by any concatenation
of natural events; but the suggestions that organisms had had from the
beginning innate in them a power of modifying themselves, their organs
and their instincts so as to meet these multifarious requirements does
not materially differ from the more overt appeals to supernatural
intervention.
The conception, originally introduced by Hering and independently by
S. Butler, that adaptation is a consequence or product of accumulated
_memory_ was of late revived by Semon and has been received with some
approval, especially by F. Darwin. I see nothing fantastic in the notion
that memory may be unconsciously preserved with the same continuity
that the protoplasmic basis of life possesses. That idea, though purely
speculative and, as yet, incapable of proof or disproof contains
nothing which our experience of matter or of life at all refutes. On
the contrary, we probably do well to retain the suggestion as a clue
that may some day be of service. But if adaptation is to be the product
of these accumulated experiences, _they must in some way be translated
into terms of physiological and structural change_, a process frankly
inconceivable.
To attempt any representation of heredity as a product of memory is,
moreover, to substitute the more obscure for the less. Both are now
inscrutable; but while we may not unreasonably aspire to analyse
heredity into simpler components by ordinary methods of research, the
case of memory is altogether different. Memory is a mystery as deep
as any that even psychology can propound. Philosophers might perhaps
encourage themselves to attack the problem of the nature of memory by
reflecting that after all the process may in some of its aspects be
comparable with that of inheritance, but the student of genetics, as
long as he can keep in close touch with a profitable basis of material
fact, will scarcely be tempted to look for inspiration in psychical
analogies.
For a summary of the recent evidence I may refer the reader to Semon's
paper[1] where he will find a collection of these observations described
from the standpoint of a convinced believer. At the outset one cannot
help being struck by the fact that of the instances alleged, very few,
even if authentic, show the transmission of acquired modifications
which can in any sense be regarded as adaptative, and many are examples
not so much of a transmission of characters produced in the parents as
of variation induced in the offspring as a consequence of treatment
to which the parents were submitted, the parents themselves remaining
apparently unmodified. No one questions the great importance of evidence
of this latter class as touching the problem of the causes of variation,
but it is not obvious why it is introduced in support of the thesis that
acquired characters are inherited.
It is most difficult to form a clear judgment of the value of the
evidence as a whole. To doubt the validity of testimony put forward
by reputable authors is to incur a charge of obstinacy or caprice;
nevertheless in matters of this kind, where the alleged phenomena are,
if genuine, of such exceptional significance, belief should only be
extended to evidence after every possible source of doubt has been
excluded. We believe such things when we must, but not before. At the
very least we are entitled to require that confirmatory evidence should
be forthcoming from independent witnesses. So far as I have seen, this
requirement is satisfied in scarcely any of the examples that have been
lately published, and until it is, judgment may reasonably be suspended.
In some cases, however, the facts are not doubtful. Standfuss, by
subjecting pupae of _Vanessa urticae_ to cold, produced the now
well-known temperature-aberrations in which the dark pigment is greatly
extended. He put together in a breeding-cage 32 males and 10 females
showing this modification in various degrees. Two of these females died
without leaving young. Seven produced exclusively normal offspring. From
the eighth female 43 butterflies were bred, and of these there were four
(all males) which to a greater or less extent exhibited the aberrational
form.[2] The mother of this family was the most abnormal of the 10
females originally put in.
Fischer's experiment with _Aretia caja_ was on similar lines. From
pupae which had been frozen almost all the moths which emerged showed
aberrational markings. A pair of these mated and produced 173 young
which pupated. Those which emerged early were all normal, but of those
which emerged late, 17 had in various degrees abnormal markings like
those of the parents.[3] In neither of these examples is there any
question as to the facts. Both observers have great experience and give
full details of their work.
As regards _Vanessa urticae_, however, it must be recalled that Fischer
himself showed that in Nymphalids somewhat similar aberrations could be
produced both by heat and by cold, and even by centrifuging the pupae.
Frl. von Linden produced a transitional form of the same aberration
in _V. urticae_ by the action of carbonic acid gas.[4] It is highly
probable that the appearance is due to a morbid change, perhaps an
arrest of development, which may be brought about by a great diversity
of causes. In the experiments the cause probably was a diseased
condition of the tissues of the mother herself. She had been subjected
to freezing sufficiently severe to prevent the proper development of
the pigments and some of the ovarian cells presumably suffered also.
It will be observed that the only specimens which were affected were
the offspring of the most abnormal female, and of them only four out of
forty-three showed any change.
The same interpretation probably applies to the cases in _Arctia caja_.
In this species the markings are well known to be liable to great
variation. As Barrett says, even in nature individuals are rarely quite
alike, and an immense number of strange forms occur in collections.[5]
These are greatly sought after by some collectors, especially in
England, where they fetch high prices at auctions, and it is notorious
that most of them come from Lancashire and the West Riding of Yorkshire.
It is commonly supposed that the breeders of that district subject them
to abnormal conditions, and especially to unnatural feeding, but I know
no clear evidence that this is true. From whatever cause it is certain
that the natural pattern is, in some strains at all events, very easily
disturbed.
The elaborate experiments of Schröder with _Abraxas grossulariata_ are
difficult to follow and are complicated by the fact that the series
which was submitted to abnormal temperatures was derived from an
abnormal original pair. From the evidence given it is not clear to me
whether the temperature had a distinct effect. This insect, like _Arctia
caja_, produces an immense number of variations (especially in the
amount of the black pigment) and as most of these are, I believe, reared
in domestication for sale, it is highly probable that the species is
easily influenced by cultural conditions.
Schröder describes two other experiments which have been accepted
by Semon and other supporters of the view that acquired characters
are transmitted. In the first, _Phratora vitellinae_, a phytophagous
beetle living on the undersides of leaves, was used. It naturally
feeds on _Salix fragilis_, a species without a felt, or tomentum, on
the underside of the leaves. Larvae were transferred to another willow
(near _S. viminalis_) which has the undersides of the leaves felted. The
larvae took readily to the new food, pushing the tomentum before them as
they gnawed the leaves. They came to maturity and when they were about
to lay their eggs they were given a free choice between _S. fragilis_
and the tomentose species. The greater number of ovipositions, 219,
took place on _fragilis_, and there were 127 on the tomentose bush,
which we are told was six times as large as the _fragilis_. The larvae
from _fragilis_ were next put on the tomentose species and reared on
it. When they became imagines they were similarly given their choice,
with the result that there were 104 ovipositions on the tomentose
species and only 83 on _fragilis_. In the next generations there were 48
ovipositions on the tomentose and 11 on _fragilis_. Finally the fourth
generation made 15 ovipositions on the tomentose and none on _fragilis_.
The difficulty about such experiments is obviously that one has no
assurance that the change of instinct, in so far as there is any,
may not be a mere consequence of the captivity. It must, besides, be
extremely difficult to arrange the experiment so that there is really
an equal choice between the two bushes, when one stands beside the
other. Przibram, in quoting this case, considers that as the tomentose
bush was about six times as large as the _fragilis_, some indication of
the relative attractiveness of the two may be obtained by dividing the
ovipositions on the larger bush by six, but I imagine the matter must be
much more complex.
Schröder's second example is not more convincing, in my opinion, though
Semon regards it as one of the most important pieces of evidence. It
concerns a leaf-rolling moth, _Gracilaria stigmatella_, the larva of
which is said normally to make its house by bending over the _tips_ of
the sallow leaves on which it feeds. Schröder placed larvae on leaves
from which the tips had been cut, and these larvae made their houses by
rolling over the _sides_ of the leaves. Their offspring were again fed
on leaves without tips, and as before, they rolled in the leaf-margins
either on one side or both. The offspring of this second generation were
then fed on entire leaves. There were 19 houses made by these (?19)
larvae, and of them 15 were normal, made by folding down the tips of
the leaves, while 4 were abnormal, made by rolling in the leaf-margins.
Schröder says that in nature he has only twice seen abnormal houses; but
it is clearly essential not only that the frequency of such variability
in nature should be thoroughly examined, but also that we should know
whether when the species is bred in captivity these irregularities of
behaviour do or do not occur when the larvae are fed on uninjured leaves.
The famous case of Schübeler's wheat is revived by Semon. The story will
be familiar to most readers of the literature of the subject. Briefly
it is that annuals, especially wheat and maize, raised from seed in
Central Europe take more time in coming to maturity and ripening than
similar plants raised in Norway, where the summer days are much longer.
The received account is that he imported seed especially of maize and
of wheat from Central Europe to Norway and found that in successive
years the period of growth and ripening was increasingly reduced. After
two generations seed of the accelerated wheat was sent back to Breslau
where it was grown, and was found to ripen rather more slowly than in
Norway, but much more quickly than the original stock had done. The
facts recorded by Schübeler[6] are that he received seed from Eldena,
which is on the Baltic near Greifswald. The variety is described as
"_100 tägiger Sommer Weizen_," but no more exact record of its behaviour
in Germany is given. This wheat, grown at Christiania in 1857, took
103 days to harvest. Its seed was again grown in Christiania in 1858,
and took 93 days, and sown again in 1859 it took only 75 days, 28 days
less than in the first year of cultivation in Norway. Seed of the 1858
crop was sent to Breslau, and grown there by Roedelius in 1859; it
took 80 days. Evidently before such a record can be used as proving an
inheritance of acquired characters numbers of particulars should be
forthcoming. The view that Johannsen has taken is that the result was
probably due to unconscious selection of the earlier individuals among a
population consisting of many types of various compositions. Some effect
may no doubt be ascribed to that cause, but I cannot think that alone
it would account for the results. My impression is rather that they
were produced by differences in the cultivation and especially in the
seasons. Research of an elaborate character would be necessary in order
to eliminate the various sources of error, and nothing of the kind has
been done; nor does Semon allude to these difficulties in prominently
adducing Schübeler's evidence. A difference of even three weeks in time
of harvesting may easily be due to variation in the season. It would in
any case be difficult to analyse the meteorological conditions, and to
decide how much effect in postponing or accelerating the harvest might
be due to cold days, to cloudy days, to wet weather, to fluctuations in
average temperature, to hot days, and other such incidents occurring at
the different periods of growth, even if they were specially watched
while the experiments were in progress, and at this distance of time
such analysis is practically impossible. Without careful simultaneous
control-experiments this evidence is almost worthless. The director of
the Meteorological Office[7] has, however, kindly sent me some details
of the weather at Breslau from 1857 to 1860, and I notice that as a
matter of fact July, 1859, was an exceptionally hot month, _having an
average of 2.67° C. above the mean_ for the twenty years 1848-1867. June
in that year was slightly (0.31° C.) below the mean and May slightly
above it (0.18° C.). August was also abnormally hot, 2.35° C. above the
average. The Breslau wheat was sown on _May 19_ and harvested on August
6. There was a cold spell from May 11 to 14, which this wheat escaped,
as it was sown on May 19. In the other years the cold spell came much
later. These elements of the weather may possibly have done something to
hurry the ripening in 1859. It unfortunate that we are not told how long
similar wheat from Breslau seed took to ripen in that year.
As regards the Norway cultivations we have the average monthly
temperatures recorded by Schübeler, though he does not discuss them
in connection with this special problem. It is quite clear that 1857,
in which the period was 103 days, was an exceptionally cold summer,
especially as regards the months of June and July, but though there
was, so far as the temperature records go, no great difference between
1858 and 1859, the year 1859, in which the period of ripening was the
shortest, was somewhat colder in Norway than 1858. But we have the
further difficulty that there were ten days difference in sowing, for
in 1858 the sowing was made on May 14, and in 1859 on May 24. With
all these possibilities uncontrolled, and indeed unconsidered, I am
surprised that Semon should claim these experiments as one of the chief
supports for his views.
Schübeler's other allegations respecting the influence of climate on
plants grown in various places and especially at different elevations
in Norway have been destructively criticised by Wille[8] to whose paper
readers interested in the subject should refer.
Before the appearance of Wille's criticisms Wettstein[9] made a
favourable reference to Schübeler's work, accepting his conclusion. He
states also that he has himself made analogous experiments with flax,
finding that the length of the period of development and a series of
morphological characters show an adaptation to local conditions, and
that on transference of seed to other conditions the previous effects
are maintained. No details, however, are given, and I do not know if
anything more on the subject has appeared since. The other examples
cited by Wettstein, such as the observations of Cieslar on forest-trees
and those of Jakowatz on gentians seem to me open to all the usual
objections applicable to evidence of this kind. Such work, to be of any
value for the purpose to which it is applied, must be preceded by a
study of the normal heredity and of the variations of the species.
Most of the recent writers (Semon, Przibram, etc.) on the inheritance
of acquired characters accept the story of Brown-Séquard's guinea pigs,
which are said to have inherited a liability to peculiar epileptiform
attacks induced in their parents by various nervous lesions.
The question has been often debated and several observers have repeated
the experiments with varying results, some failing to confirm
Brown-Séquard, others finding evidence which in various degrees
supported his conclusions. Recently a new and especially valuable paper
has been published by Mr. T. Graham Brown[10] which goes far towards
settling this outstanding question. He states that "the Brown-Séquard
phenomenon is nothing more or less than a specific instance of the
scratch-reflex," and it is due to a raised excitability of the mechanism
of this reflex. This raised excitability is the character acquired as a
consequence, for instance, of the removal of part of one great sciatic
nerve. The nature of this raised excitability and its causation are
discussed and elucidated, but this part of the work is not essential
to the present consideration. Mr. Graham Brown in his summary of
conclusions remarks that it is very difficult to see how this condition
of raised excitability can be transmitted to the offspring, and this
comment which might be made in reference to any of the alleged cases
certainly applies with special cogency to the present example.
He then calls special attention to three observations:
1. That guinea pigs which had a "trophic" change in the foot, as a
result of division of the great sciatic nerve, have repeatedly been seen
to nibble the feet of other guinea pigs which had this change in the
foot from the same causes.
2. That accidental injury to the toes may be followed by the
Brown-Séquard phenomenon in an otherwise normal animal.
3. That in several instances the young of guinea pigs which exhibited
the phenomenon have been noticed to have one or more toes eaten off by
the mother.
Brown-Séquard noticed that almost all his animals in which the great
sciatic was divided acquired the "epilepsy" and nibbled those parts of
their feet in which sensation had been lost. Of the offspring of such
animals he found that a very small proportion exhibited a malformation
of the feet, and of these some showed the "epilepsy." The proportion
which showed the "epilepsy" was one to two per cent. of the offspring.
Morgan[11] is quoted by Graham Brown as having suggested that the
loss of toes in the offspring may have been due to mutilation by the
mother, following his experience in a case in which the tails of mice
in succeeding litters were thus devoured, and there can be little doubt
that in this suggestion lies the clue to the explanation of the whole
mystery. Graham Brown concludes that it may be supposed with every
degree of probability that the "transmission" was due to injuries
inflicted upon the young by their parents. With this conclusion most
people will now be disposed to agree, and we may hope that we shall
hear the last of this curious myth--to the elucidation of which a vast
quantity of research has been devoted.
The series of experiments made by Kammerer with various Amphibia have
attracted much attention and have been acclaimed by Semon and other
believers in the transmission of acquired characters as giving proof of
the truth of their views. With respect to these observations the chief
comment to be made is that they are as yet unconfirmed. Many of the
results that are described, it is scarcely necessary to say, will strike
most readers as very improbable; but coming from a man of Dr. Kammerer's
wide experience, and accepted as they are by Dr. Przibram, under whose
auspices the work was done in the Biologische Vesuchsanstalt at Vienna,
the published accounts are worthy of the most respectful attention.
The evidence relates chiefly to three distinct groups of occurrences:
1. Modification in _Alytes obstetricans_, the Midwife Toad, affecting
both the structure and the mode of reproduction, induced by compulsory
change of habits.
2. Modification in the mode of reproduction of _Salamandra atra_ and
_maculosa_ induced by compulsory change of habits.
3. Modification in the colour of _Salamandra maculosa_ induced by change
in the colour of the soil on which the animals were kept.
1. I will take first the case of _Alytes_,[12] because it is the most
definite example, and because it is the case which most readily admits
of repetition and verification.
The habits of _Alytes obstetricans_ are well known. The animals copulate
on land. As the strings of eggs leave the female they are entangled by
the hind legs of the male, and being adhesive they stick to him and
undergo their development attached to his back and legs. The number of
eggs varies from 18 to 86, a number much smaller than is usual in toads
and frogs which lay their eggs in water. The eggs are large and full of
yolk.
There are two breeding seasons, one about April and the other about
September, and a winter hibernation. Not only animals brought in from
outside, but their offspring reared in domestication maintain these
normal habits in confinement, if the temperature does not exceed 17° C.
(pp. 499 and 534).
If, however, the temperature be artificially raised and kept at 25-30°
C., the males do not attach the eggs to themselves when spawning occurs
on land but let them lie. The adhesion of the eggs is said to be
hindered by the comparatively rapid drying of their surfaces.
More usually in the high temperatures the animals _take to the water_
and copulate there. The eggs are ejected into the water, and as their
gelatinous coverings immediately swell up, they do not stick to the
males.
The offspring thus derived from the parents subjected to heat for one
breeding-period only, whether they were laid in water or on land, did
not show departures from the normal type.
Kammerer states next, however, that in subsequent breeding-periods the
same parents frequently take to the water to breed, though they have
become quite accustomed to the heated chamber; and furthermore that if
such animals, having thus lost their instinct to brood their young, be
transferred to ordinary temperatures they do not readily reassume their
normal habits, but for several breeding seasons--at least four--will
take to the water. These parents lay from 90 to 115 eggs, which are
small and contain little yolk, and the larvae, on hatching, breathe with
their embryonic gills until they are absorbed instead of being broken
off as normally.
The offspring thus abnormally developed when they mature are said never
to brood their eggs. If they are derived from the earlier spawnings of
their parents, before, that is to say, the parents had been submitted
to the changed conditions long enough to transmit their effects, they
lay on land; but if they are derived from the later spawnings, they
lay in the water. These changes of habit are manifested without the
continued application of the abnormal experimental conditions, and, as I
understand the account, in normal conditions of temperature.
If the abnormal experimental conditions are continued, the toads always
lay in water, and their eggs become progressively smaller and more
numerous. The larvae in the fourth generation acquire three pairs of
gills instead of one pair, and are in other respects also different from
the normal form.
Respecting the _Alytes_ bred in this way Kammerer makes the very
striking statement that _the males in the third generation_ (p. 535)
_have roughened swellings on their thumbs and that in the fourth
generation_ (pp. 516 and 535) _these swellings develop black pigment_.
Together with the appearance of this secondary sexual character there
is hypertrophy of the muscles of the fore-arm. To my mind this is
the critical observation. If it can be substantiated it would go far
towards proving Kammerer's case. _Alytes_, among toads and frogs, is
peculiar in that the males do not develop these lumps in the breeding
season, and the fact may no doubt be taken to be correlated with the
breeding habits, copulation occurring on land and not in water as is
usual with Batrachians. It is to be expressly noticed that these lumps
on the thumbs or arms of male toads and frogs are not merely pigmented
swellings, but are pads bearing numerous minute horny black spines,
which are used in holding the females in the water. The figures which
Kammerer gives (Taf. XVI, figs. 26 and 26a) are quite inadequate, and as
they merely indicate a dark patch on the thumbs it is not possible to
form any opinion as to the nature of the structure they represent.
The systematists who have made a special study of Batrachia appear to
be agreed that _Alytes_ in nature does not have these structures; and
when individuals possessing them can be produced for inspection it
will, I think be time to examine the evidence for the inheritance of
acquired characters more seriously. I wrote to Dr. Kammerer in July,
1910, asking him for the loan of such a specimen[13] and on visiting
the Biologische Versuchsanstalt in September of the same year I made
the same request, but hitherto none has been produced. In matters of
this kind much generally depends on interpretations made at the time
of observation; here, however, is an example which could readily be
attested by preserved material. I notice with some surprise that in a
later publication on the same subject no reference to the development of
these structures is made (see below).
The statements here given represent but a small part of Kammerer's
papers on the subject. He gives much further information as to the
course of the experiments, especially in regard to the fate of the eggs
laid on land and the aberrations induced in them by treatment. The
ramifications of the experiments are, however, very difficult to follow,
and as I am not sure that I have always understood them I must refer the
reader to the original.
More recently Kammerer has published[14] a most curious account of
experiments in crossing his modified and abnormal _Alytes_, derived from
the water-eggs, with normal individuals.
In the first case the cross was made between a _normal female_ and an
_abnormal male_. The offspring were normal in their habits. In the next
generation bred from these almost exactly a quarter showed the abnormal
instinct.
The reciprocal cross was made between an _abnormal female_ and a _normal
male_. In this case the offspring were abnormal in their behaviour; but
the second generation bred from them showed three quarters abnormal and
one quarter normal.
Certain details as to numbers and sexes of the various families bred
in the course of this amazing experiment are given in a subsequent
publication.[15] This later paper goes somewhat fully into the question
of the difference in behaviour between the normal and modified
individuals, describing the ways in which the males and females
possessing the acquired character could be recognised from the males and
females which were normal, but in this account I find no reference to
the development of the "_Brunftschwielen_"--the horny pads on the hands
of the males. As these structures would be of special value in such a
diagnosis the omission of any allusion to them calls for explanation.
Kammerer claims the evidence as proof of Mendelian segregation in
regard to an acquired character, the first example recorded. Pending a
repetition of the experiments there is no more to be said.
2. _The Mode of Reproduction of Salamandra atra and
maculosa._[16]--_Salamandra maculosa_, the common lowland form, with
yellow bands or spots, deposits its young in water, generally as
gill-bearing tadpoles, with a wide, swimming tail, though occasionally
they are born still enclosed in the egg-capsule out of which they soon
hatch. Spawning extends over a considerable period, often many weeks,
and during the season one female may bear more than 50 young.
_S. atra_, the black Alpine form, produces its young on land. They are
born without gills, ready to breathe air, and with the rounded tail
of the adult. These differences may, as Kammerer says, naturally be
regarded as adaptations to the Alpine conditions. Moreover, the female
bears _only two_ young in a season, and this reduction in the number
must be taken to be a consequence or condition of viviparity. There are
many eggs in the ovary, but all except the two which are destined to
develop degenerate and form a yolk-material on which these two survivors
feed.
Kammerer gives a long account of the various conditions to which he
subjected both species. The treatment was complicated in many ways, but
the essential statements are, as regards _S. maculosa_, that when no
water was provided in which the young might be born, they were dropped
on land, larger and in a later stage of development and of a darker
colour than is normal; that the larvae so born gradually diminished
in number until only two were deposited in each breeding-period;
that dissection showed that the other ova degenerated to form a
yolk-material. The larvae so produced reached maturity. The summary of
results describes their behaviour, stating that they produced:
(_a_) _In water_, either (1) _very_ advanced, large-headed larvae 45
mm. long (instead of 25-30 mm.) with gills already reduced, which had
awkward, embryo-like movements, and in some few days metamorphosed
into small perfect salamanders; or (2) moderately advanced, properly
proportioned larvae, 40-41 mm. long, provided with large gills of (at
first) intrauterine character, which were reduced during aquatic life.
(_b_) _On land_, small (26 mm. long) larvae with rudimentary gills,
having the body rounded instead of being flattened from above downwards,
and an elongated narrow head, which were unable to live in deep water.
These larvae changed to the salamander colour in 10-12 days, and after
four weeks metamorphosed into salamanders 29 mm. long.
(_c_) In the foregoing cases the experimental conditions were not
continued, or in other words, basins of water were provided in which
they could spawn. But if the experimental conditions are continued,
these _Salamandra maculosa_ which were born newt-like (viz., not in a
larval condition), are themselves newt-bearing from the first time they
give birth, using the dry land, and bringing forth only two young, the
normal number for the births of _S. atra_. These young are 40-41 mm.
long, and are dark-coloured, resembling greatly the normal new-born _S.
atra_.
This epitome of the observations illustrating the inheritance of
acquired characters has been very widely quoted, and may not unnaturally
be taken to summarize a wide experience of the modified animals.
Reference to the details given in the same paper shows that, as alleged,
each of the four types of behaviour enumerated was witnessed _once_ only
in the case of each of four females, no two agreeing with each other.
As to the number of the males or their habits nothing is said. The first
female, _a_ (1), bore five young; the second, _a_ (2), bore two, of
which one was a partial albino; the third, _b_, produced four young; and
the fourth, _c_, two as already stated.
In the case of _c_ the details show that the female gave birth
immediately after being transferred from the open-air terrarium to
one indoors, which contained no basin of water. This is the example
of the consequences which follow on a continuance of the experimental
conditions.[17]
As regards _S. atra_ the converse is reported. Various means were
used to induce them to eject their young prematurely in water, such
as massaging the sides of the mothers, or raising the temperature to
25° or 30° C., with various degrees of success. But afterwards it was
found that specimens collected wild at an elevation of about 1,000
metres responded to much simpler treatment, and gave birth prematurely
in water when they were kept in a large shallow basin of water not so
deep but that they could everywhere touch the bottom with their feet and
keep their heads above the surface. With specimens collected at higher
elevations this treatment was inoperative, and the suggestion is made
that _S. atra_ at the lower confines of its habitat partakes more of the
nature of _maculosa_ than do the individuals from greater heights; for
Kammerer argues that pools suitable for breeding must be more uncommon
at those elevations than they are lower down.
In the earlier paper[18] Kammerer states that newly caught females
of _S. atra_ often give birth in the water, and show an undoubted
preference for doing so. He describes also how he once saw several
females, wild in their natural habitat, lay their young in a rain-puddle
at 1,800 metres elevation, but the larvae thus born were fully formed.
When the deposition of the young as larvae has become "habitual"[19]
with _S. atra_, three to nine larvae may be produced at one spawning
period, from 35 to 45 mm. long, with gills at most 8 mm. long, and a
tail-fin 2-3 mm. broad. Such larvae are generally coffee-brown, or grey
(instead of black), and show other minor differences.
The summary states that when grown to maturity they become in their turn
larva-bearing, and go into the water to bring forth. Their young are
more than two (3 to 5 being the numbers observed) with a length of 33-40
mm. or of 21-23 mm. at birth. They are light grey, spotted (mottled with
lighter and darker colour), have relatively short gills (8 to 9 mm.
at most) and a broad tail-fin (3 mm. wide). At metamorphosis they are
relatively long (44 mm.) and one of them had some yellow pigment.
Here again this summary is, as a matter of fact, describing the
behaviour of two mothers, of which one produced three, and the other
five young.
To my mind these experiments suggest that the reproductive habits
of both species, if closely observed, will be found to be subject
to considerable variation, and I think it not impossible that each
species is, especially in confinement, capable of being a good deal
deflected from its normal behaviour. Moreover, there seems to me no
great improbability in the idea that there is an interdependence
between the number of young and the stage of maturity in which they
are born. But, at the same time, the case as told by Kammerer strikes
me as proving too much. If each species is so sensitive to conditions
that the normal procedure is gravely modified in one generation, and
if that modification can reappear in a pronounced form in the next
generation without a renewal of the disturbing conditions, it becomes
extremely difficult to understand how the regularity which each species
is believed to display in nature can be maintained. Surely both species
might be expected to be in confusion. From a passage in Kammerer's
earlier paper (1904, p. 55) on the subject, I infer that he also would
expect considerable irregularity in the natural behaviour, but that he
has not investigated the point.[20]
3. _Modification of the Colour of Salamandra maculosa induced by Change
in the Colour of the Soil on which the Animals were kept._--Kammerer
speaks of this as the most convincing of all his experiments on the
transmission of acquired characters. So far, however, no full account of
them has been published.[21] The statement is that when salamanders are
kept in yellow surroundings the yellow markings gradually in the course
of years increase in amount relatively to the black ground colour.
Conversely by keeping the animals on black garden soil, the yellow may
be greatly diminished in quantity until it largely disappears. (The
account in _Natur_ adds that very moist conditions also favour the
increase of yellow, and that with less moist conditions the yellow
diminishes.) From each kind, the (induced) yellower and the (induced)
blacker, a second generation was raised, on soil of neutral colour, and
each family was later divided into two parts, half being put on black
and half on yellow ground.
As regards the offspring of those which had lived on _black_ soil no
positive result had been reached up to the date of publication, but it
is stated that these young resembled their parents in having the yellow
distributed in _irregular spots_.
As regards the offspring of those which had lived on yellow soil the
account follows up the story of that part of the offspring which were
put on yellow soil again. It is stated that these, though derived from
parents with irregular spots, _developed the yellow as longitudinal
bands_.
This account is given with slight differences of expression in the
three places to which I have referred. On returning from Vienna in
1910 I consulted Mr. G. A. Boulenger in reference to the subject, and
he very kindly showed me the fine series from many localities in the
British Museum, and pointed out that in nature the colour-varieties
can be grouped into two distinct types, one in which the yellow of
the body is irregularly distributed in spots and one in which this
yellow is arranged for the most part in two longitudinal bands which
may be continuous or interrupted. _The spotted form is, as he showed
me, an eastern variety, and the striped form belongs to western
Europe._ Mr. E. G. Boulenger[22] has since published a careful account
of the distribution of the two forms. The spotted he regards as the
typical form, var. _typica_, and for the striped he uses the name
var. _taeniata_. The typical form occupies eastern Europe in general,
including Austria and Italy, extending as far west as parts of eastern
France. The var. _taeniata_ is found all over France, excepting parts of
the eastern border, Belgium and western Germany, Spain and Portugal. Of
the very large series examined there was only one specimen (Lausanne)
which could not with confidence be referred to one or other of the
two varieties. Mr. E. G. Boulenger points out that both varieties
inhabit very large areas, and live on soils of most different colours
and compositions. Both are liable to variations in the amount and the
shade of the yellow, but that any suggestion that _taeniata_ belongs
especially to yellow soils and _typica_ to black soils is altogether
inadmissible. He expresses surprise that Kammerer should not allude to
these peculiarities in the geographical distribution of the two forms.
He suggests further that it is more likely that some mistake occurred in
Kammerer's observations than that the east European _typica_ should, in
the course of a generation, have been transformed into the west European
_taeniata_ by the influence of yellow clay soil.
In his last paper on the subject Kammerer states incidentally[23] that
he has found the _striped form recessive to the spotted_. No evidence
for this statement is given, and I have not found any other reference
to crosses effected between the two natural types. If, however, this
representation is correct, it is conceivable that the production of
_taeniata_ from _typica_ was in fact the re-appearance of a recessive
form. The plate which Kammerer gives in illustration of his modified
parent figures a single animal at four stages, and though it is
certainly more like the spotted than the striped form, it has a certain
suggestion of the striped arrangement, such as I can well imagine being
produced in the heterozygote.[24]
In continuation[25] of the experiments on the colour of _S. maculosa_
Kammerer publishes an account of elaborate experiments in grafting
ovaries of the various forms, modified and unmodified, into each other,
and describes the offspring which followed. Before pursuing this part of
the inquiry I am disposed to wait until the earlier steps have been made
much more secure than they yet are.
More recently Kammerer has published similar statements in regard to the
inheritance of characters induced in various lizards by keeping them in
abnormal temperatures, high and low. The changes induced affected in
some species the colours, in others the reproductive habits. Respecting
these examples I feel the same scepticism that I have indicated in
regard to the others, somewhat heightened by the fact that insufficient
evidence is given both regarding the behaviour of these various species
in captivity when not subjected to abnormal temperatures, and in the
wild state.
Respecting this part of the evidence Mr. G. A. Boulenger has lately
published a criticism[26] from which I extract the following passages.
Referring to a previous note[27] on the question of the melanism of the
various insular forms of _Lacerta muralis_ he writes: "I also alluded
(_l. c._) to the theories that have been propounded to explain the
melanism of various insular forms. This is a subject which has been
lately taken up by Dr. Kammerer at the Biologische Versuchsanstalt in
Vienna, and he claims to have produced nigrinos artificially by a very
strong elevation of the temperature, accompanied by extreme dryness. Dr.
Werner[28] has already opposed his own experiments to those of Kammerer,
artificial melanism having been produced by him in _Lacerta oxycephala_
by keeping two very light specimens from Ragusa for a whole summer
in very damp conditions. Neither is Kammerer's theory in accordance
with the distribution of the black lizards, as pointed out by Werner.
Kammerer also finds that those forms which are known to produce melanic
races in a state of nature, lend themselves more readily than the others
to the success of his experiments. But he shows himself misinformed
when he states that the variety called _Lacerta fiumana_ belongs to the
category of those of which black forms are not known. He overlooks the
fact, first pointed out by Scherer in 1904, and which I can confirm,
that the black lizard from Melisello near Lissa in the Adriatic is
unquestionably derived from the lizard from Lissa, which he correctly
regards as not separable from _L. fiumana_...."
"Another colour modification which Dr. Kammerer states that he obtained
by raising the temperature is the assumption by the female of the
typical _Lacerta muralis_ of the bright red colour of the lower parts
which often distinguishes the male from the female, and which was not
shown by the individuals of the latter sex kept by him under normal
conditions. He quotes various authorities to show that the lower parts
are never red in the females, but he has omitted to consult others who
say the contrary. Thus Bedriaga (1878 and 1879) remarks that a so-called
var. _rubriventris_ of the typical wall lizard has the lower parts red
in both sexes."[29]
In reading such papers as those of Semon or Kammerer the thought
uppermost in my mind is that to multiply illustrations of supposed
transmission of acquired characters is of little use until some one
example has been thoroughly investigated. If we had certain assurance
that even a single unimpeachable case could be repeated at will, the
whole matter would assume a more serious aspect. If, for instance,
Kammerer were able to show us _Alytes_ males with horny pads on their
hands, it would be something tangible; still more, if the experiment
were repeated by others until no doubt remained that the offspring
of _Alytes_ which had bred in water for some three generations did
acquire these pads and that they could transmit these novelties to
descendants raised in normal conditions. Till evidence of this kind is
published by at least two independent observers investigating similar
material, I find it easier to believe that mistakes of observation or
of interpretation have been made than that any genuine transmission of
acquired characters has been witnessed.
Meanwhile there is no denying that the origin of adaptational features
is a very grave difficulty. With the lapse of time since evolutionary
conceptions have become a universal subject of study that difficulty
has, so far as I see, been in nowise diminished. But I find nothing in
the evidence recently put forward which justifies departure from the
agnostic position which most of us have felt obliged to assume.[30]
APPENDIX TO CHAPTER IX.
Professor G. Klebs, as is well known to students of evolutionary
phenomena, has for several years been engaged in investigations relating
to the inheritance of acquired characters. In his many publications
on the subject the issue has always been represented as more or less
uncertain.
Desiring to know how the matter now stands according to Professor Klebs'
present judgment I wrote to him asking him to favour me with a brief
general statement. This he most kindly sent in a letter dated 8th July,
1912.
As such a statement will be read with the greatest interest by all who
are watching the progress of these studies I obtained permission to
publish it as follows:
8. Juli 1912
Ihre liebenswurdige Anfrage will ich sehr gern
beantworten, obwohl ich sie nicht so beantworten kann wie ich
erwünschte. Ihr Skepticismus in der Frage der Uebertragung
erworbener Charactere auf die Nachkommen ist nur zu berechtigt.
Meine Versuche mit Veronica sind _nicht_ beweisend, da es mir
bisher nicht gelungen ist eine einigermasse konstante Varietät
mit verlaubten Inflorescenze zu erzeugen. In Bezug auf mein
Semper vivum bin ich allerdings noch heute der Meinung dass
die starke künstliche Veränderung der Blüte einen Einfluss auf
einzelnen Nachkommen gehabt hat. Ich habe seither nichts darüber
veröffentlicht: die Mehrzahl der anormalen gefüllten Blüten war
leider steril. Von einem weniger veränderten Exemplar erhielt
ich einige Sämlinge, aber sie haben noch nicht geblüht. Es kann
sich in diesem Falle nur um eine _Nachwirkung in der ersten
Generation_ handeln, vergleichbar jenen Fällen in denen Samen von
Bäumen aus den hohen Alpen in der Ebene gewisse Nachwirkungen
zeigen. Aber es ist bisher kein sicherer. Fall bekannt in den
der kunstliche herbeigeführte Charakter _mehrere Generationen
hindurch unter der gewöhnlichen "normalen" Bedingungen_
übertragen worden ist.
Auf der andere Seite sind diese negativen Resultaten nicht
entscheidend. Denn wie wenig ist in dieser Beziehung überhaupt
ernstlich versucht worden! Und zweifellos geht die Sache nicht so
einfach.
Ich versuche es mit anderen Pflanzen weil ich der Meinung bin
dass es möglich sein müsse wenigstens solche neuen Varietäten zu
erzeugen, wie sie die Gartenvarietäten entsprechen.
Aber bis jetzt leider sind die Versuche nicht gelungen, weder
mir noch irgend einem anderen.
FOOTNOTES:
[1] Semon, R., Der Stand der Frage nach der Vererbung erworbener
Eigenschaften, published in _Fortschr. der naturw. Forschung._, Bd. 11,
1910.
[2] Standfuss, M., _Denks. Schweiz. naturf. Ges._, XXXVI, 1898, p. 32.
[3] Fischer, E., _Allg. Ztschr. f. Entomologie_, Bd. VI, 1901.
[4] Out of 12 pupae treated 8 died and of the 4 survivors, one only was
affected. See M. v. Linden, _Archiv. Rassen. u. Gesells._, 1904, I.
[5] For illustrations see _Oberthur's Études d'Entom._, 1896, where many
of these curious aberrations are represented; also Barrett, _Lepid.
Brit. Islands_, II, pp. 71 and 72.
[6] Schübeler, F. C., _Die Culturpflanzen Norwegens_, 1862, especially
pp. 24 and 28.
[7] I am obliged to him and to Dr. E. Gold for much trouble taken to
answer my questions. Some idea of the kind of weather indicated by an
average of 2.76° C. above the mean may be got from a comparison with the
year 1911, which most people will remember as one of the hottest summers
they have known. The July of that year was in east and southeast England
about 4° F. above the mean but 2.67 C. means about 4.8° F. above the
mean. At Greenwich July, 1859, was about 6.5° F. above the average.
[8] Wille, N., _Biol. Cbltt._, XXV, 1905, p. 521.
[9] Wettstein, R. von. _Der Neo-marckismus u. seine Beziehungen zum
Darwinismus_, Jena, 1903.
[10] T. Graham Brown, _Proc. Roy. Soc._, 1912, vol. 84, B, p. 555. This
paper gives full reference to the previous literature of the subject.
[11] Morgan, T. H., _Evolution and Adaptation_, New York, 1903.
[12] Kammerer's chief paper on this subject is in _Arch. f. Entwm._,
1909, XXVIII, p. 447, and it is to this that the paginal references in
the present text relate. His previous paper appeared, _ibid._, 1906,
XXII, p. 48. An account of his further experiments with _Alytes_ is
given in _Natur_, 1909-10, Heft 6, p. 95.
[13] In reply to my letter Dr. Kammerer who was then away from home
very kindly replied that he was not quite sure whether he had killed
specimens of _Alytes_ with "_Brunftschwielen_" or whether he only
had living males of the fourth generation, but that he would send
illustrative material.
[14] Kammerer, P., _ Natur_, 12 December, 1909, Heft 6, p. 95, repeated
in _12 Flugschrift d. Deutsch Ges. f. Züchtungskunde_, Berlin, 1910.
[15] _Festschrift zum Andenken an Gregor Mendel_, being vol. XLIX of the
_Verh. Naturf. Ver. in Brünn_, 1911, p. 98.
[16] Kammerer's chief papers on this subject are _Archiv fur Entwm._,
XVII, 1904, and _ibid._, XXV, 1907. An epitome of results is also given
by him in _12 Flugschrift d. Deutsch. Ges. f. Züchtungskunde_, Berlin,
1910.
[17] "_Bei Fortdauer der Versuchsbedingungen sind als Vollmolche
geborene Salamandra maculosa_ gleich bei der ersten Geburt _abermals
voll molchgebärend_, benutzen zum Geburtsakt das trockene Land,
und zwar unter Erreichung der (bei _Salamandra atra_ normalen)
_Embryonen-Zweizahl_," Kammerer, 1907, p. 49.
[18] 1904, p. 56.
[19] Throughout Kammerer's papers this is used almost as a technical
term. It means, I presume, that the feature was manifested more than
once.
[20] It should be stated that the papers contain a quantity of detail,
especially descriptive of the state of the larvae, which I have not
attempted to represent, but the account here given contains all that
seemed essential to an understanding of the more important features of
the account.
[21] The first appeared in _Natur_, 1909-10, Heft 6, p. 94; and the
second, which contains coloured plates of the animals, in the lecture
already referred to, _12 Flugschr. d. Deut. Ges. f. Züchtungkunde_,
Berlin, 1910, p. 26. In the paper in _Mendel Festschrift_, 1911, the
subject is continued, but no more is added as to this part of the
experiment.
[22] E. G. Boulenger, _Proc. Zool. Soc._, 1911, p. 323.
[23] _Mendel Festschrift_, 1911, p. 84.
[24] _12 Flugschrift. Deut. Ges. Züchtungskunde_, 1910, Fig. 15, _P.
Reihe_.
[25] _Mendel Festschrift_, 1911, p. 83.
[26] Field, 1912, 30 March.
[27] _Ibid._, 1904, p. 863.
[28] _Mitth. Naturw. Ver. a. d. Univ. Wien_, 1908, p. 53.
[29] As to the variations of _Lacerta muralis_ in Western Europe and
North Africa see Boulenger, G. A., _Trans. Zool. Soc._, 1905, vol. XVII,
p. 351.
[30] As to the experiments of Klebs relating to the transmission of
acquired characters, see Appendix.