Copyright
Vernon L. (Vernon Lyman) Kellogg.

Darwinism to-day; a discussion of present-day scientific criticism of the Darwinian selection theories, together with a brief account of the principal other proposed auxilary and alternative theories of species-forming online

. (page 28 of 38)
Online LibraryVernon L. (Vernon Lyman) KelloggDarwinism to-day; a discussion of present-day scientific criticism of the Darwinian selection theories, together with a brief account of the principal other proposed auxilary and alternative theories of species-forming → online text (page 28 of 38)
Font size
QR-code for this ebook


cells was originally due to the absence of light, and that the change
has now become hereditary. The pigment-cells produced by the
action of light on the lower side are in all respects similar to-
those normally present on the upper side of the fish. If the dis-
appearance of the pigment-cells was due entirely to the variation
of the germ-plasm, no external influences could cause them to re-
appear; and if there were no hereditary tendency, the coloration
of the lower side of the flatfish would be rapid and complete."

Concerning Fischer's highly interesting experimental work, I
quote the following paragraph from Fuchs, H. (Biol. Centralbl.,

Fischer's ex- Vol. XXI, pp. 591-592, 1901; Fischer's own papers
periments with have been published in various biological journals,
butterflies* t jj e particular one recounting the results obtained

with Arctia caja in the Allg. Zeitschr. fur Entomologie, Vol.
VI, 1902) :

"Experimented Untersuchungen, ob es moglich sei, durch will-
kiirliche, geeignet gewahlte Veranderungen der 'ausseren Lebens-
bedingungen,' besonders der Temperaturverhaltnisse, im Tierreiche



OTHER THEORIES OF SPECIES-FORMING. 297-

Variationen bei den Arten hervorzurufen, wurden in den letzten
Decennien wiederholt angestellt; mit Vorliebe hat man sich dabei
als Versuchsobjekte die Schmetterlinge gewahlt : ich erinnere z.
B. an die schonen Versuche von Standfuss und E. Fischer. Das
Resultat war wie ja nach unseren heutigen Anschauungen iiber
den ziichtenden Einfluss der Faktoren der Aussenwelt auf alle
Organismen eigentlich kaum anders zu erwarten stand positiv.
Eine Fyage allerdings, an welche bei diesen Untersuchungen wohl
jeder der Forscher dachte, namlich : ob die auf solche Weise
erworbenen Eigenschaften und Abanderungen auch auf die eventu-
ellen Nachkommen iibertragen, also vererbt wurden oder doch
wenigstens werden konnten, blieb dabei einstweilen unentschieden.
Erst kiirzlich gelang es E. Fischer, auch fur dieses Postulat der
modernen Biologic einen vollgiltigen Beweis beizubringen. F. expe-
rimentierte mit Arctia caja, dem braunen Bar, der ja auch den
meisten Laien meist wohl unter dem Namen 'deutscher Bar'
bekannt sein durfte, ein erfahrungsgemass fur kiinstliche Varia-
tionsversuche besonders geeignetes Tier. Durch willkiirlich ge-
wahlte Temperaturveranderungen, und zwar durch intermittierende
Abkiihlungen bis auf 8 C, denen die Puppen wiederholt ausge-
setzt wurden, erzielte F. stark aberrative Falter, und zwar aberrativ
nicht nur beziiglich der 'Farbe und Zeichnung' wenn auch hier in
erster Linie. sondern auch beziiglich der Form, z. B. der Flugel
und der Beine. Dabei hebt F. ausdriicklich hervor, dass in letzterer
Hinsicht es sich nicht etwa um Verkruppelungen handelte, sondern
'die Fiisse waren kraftig und mit gut ausgebildeten Krallen
versehen.' Unter diesen Varietaten gelangen nun mehrfache
Kreuzungen ; die Puppen dieser Zucht wurden unter normalen
Bedingungen erhalten. Und siehe ! von den alsbald ausgeschliipften
Tieren zeigte eine nicht unerhebliche Anzahl die Variationen der
Eltern, und zwar im allgemeinen als Kombinationen aus den
veranderten Eigenschaften beider Eltern, so dass einige mehr dem
elterlichen Mannchen glichen, andere mehr dem elterlichen Weib-
chen. Es ist dieses also, wie F. sagt, ein experimenteller Beweis,
dass :

"i. die Art durch die Faktoren der Aussenwelt Veranderungen
erfahrt, und dass

"2. diese Veranderungen sich auf die Nachkommen iibertragen.

"Die Thatsache der Vererbung erworbener Eigenschaften steht
mithin fest, wenn wir auch iiber das Wesen der ratselhaften dabei
stattfindenden Vorgange, auf Grund dieser Untersuchungen, natiir-
lich absolut noch nichts sagen konnen."

To the above cases of the alleged inheritance of acquired charac-
ters I may add some account of certain experiments with the mul-



298 DARWINISM TO-DAY.

berry silkworm carried on by R. G. Bell and myself. (For detailed ac-
count of this work see Science, N. S., Vol. XVIII, pp. 741-748, 1903-)

"One of the races of the mulberry silkworm, Bombyx mori, has
been the subject of experiments directed toward a determination of
the exact quantitative relation which quantity and quality of food
bear to the development and variations of the individual insect and
its progeny. . . .

"The insect, Bombyx mori, has a complete metamorphosis, tak-
ing no food as an adult, so that the experimental control of the
Experiments feeding has been necessary only during the larval or
with silkworms, 'silkworm' stage. The larval life is subdivided into
five stages clearly set off from one another by the intervening
moults, of which there are normally four, and these substages have
been useful when an alteration of food conditions during a sharply de-
nned shorter time than the entire larval life was desirable. . . . The
change in quantity of food has consisted in altering the amount of
mulberry leaf served to the larvae, the control of which has been
secured as follows: It has been determined through experience with
normal larvae that each will consume a certain amount of food in
a certain number of hours (increasing in amount with the increas-
ing age and size of the larva), this amount representing the
optimum amount of food for the normal individual and necessitating
as many daily meals as are required to keep any but the moulting
larva constantly supplied with fresh food. This amount determined,
a tolerably definite small proportion of the optimum amount has
been allotted the individuals which were sentenced to short rations,
which, roughly speaking, might be listed as one-quarter the optimum
amount during earlier stages and one-eighth during the late larval
stages. This one-fourth, one-eighth, or whatever it may have been
numerically, was, at any rate, as small an amount of food as was
compatible with mere life. . . .

"These experiments have extended over a period of three years,
covering as many generations of the insect. The data gathered
(being the measurements, weight, and duration of each larva in each
of its five states; the time of spinning, weight of silk and weight
and duration of each pupa ; and the weight, size, pattern, and
fertility of female of each imago) furnish material, then, for a
study of the effects of under-feeding upon individuals during a
single generation (the 1903 generation or that of 1902 or 1901),
during two successive generations (1901-02 or 1902-03), and two
alternating generations (1901-1903) and during three generations
(1901703), a control lot having been carried for each experimental
lot so that what is modified may confidently be distinguished from
what is normal. .



OTHER THEORIES OF SPECIES-FORMING. 299

"In these variously-fed worms there exists a very definite and
constant relation between amount of food and size as indicated by
weight, the starveling individuals being consistently smaller than
the well-nourished, the lingering effects of this dwarfing being
handed down even unto the third generation, although the progeny
of the famine generation be fed the optimum amount of food; in
case the diminished nourishment is imposed upon three, or even
two successive generations, there is produced a diminutive, but
still fertile, race of Lilliputian silkworms, whose moths, as regards
wing expanse, might join the ranks of the micro-Lepidoptera
almost unremarked.

"In illustration may be quoted the typical or modal larval weights
for each of the lots of 1903 at the time of readiness to spin, which
marks the completion of the feeding and is, therefore, an advan-
tageous point for a summary of the results of the three years'
experimental feeding.

"The history of the eight lots referred to may be gathered from
an examination of the accompanying table, in which 'O' means
optimum amount of food and 'S' means short rations. The column
to the right indicates the relative rank of the various lots as judged
by the modes of frequency polygons erected to include all the
individual weights for each lot at spinning time.



Lot Number.


HISTORY OF LOTS.


Modal Rank.
1903.


igoi.
Grandparents.


1902.
Grandparents.


1903.


I



O

o



s
s
s
s




o

s
s
o
o

s
s




s
o
s



s
o
s


I
6
3
7

2

5
4

8


2


i




5


6


1


3





"We find that control lot I, consisting of normally-fed indi-
viduals of normal ancestry, holds first rank in weight, as was to be
expected. Second comes lot 5, whose grandparents experienced a
famine but whose parents as well as themselves enjoyed years of
plenty. Lots 2 and 3 have likewise had one ancestral generation on
short rations, and the fact that they are lighter in weight than lot



300 DARWINISM TO-DAY.

5 illustrates a general rule which obtains throughout the entire
company of experimental worms, namely, that the effects of famine
grow less evident the further removed the individuals are from its
occurrence in their ancestral history. Thus lot 5 is two generations
removed from the famine of 1901, while lot 3 has had but one
generation in which to recover its ancestral loss. Lot 2, which
has had a total of but one famine year the current year neverthe-
less ranks below lot 7, which has had two famine years in its
ancestry succeeded by plenty during the current year. 'Lot 2 also
ranks below lot 6, a fact which appears strange, considering that
lot 6 has suffered two generations of famine, including the current
year, which is the only famine year experienced by lot 2. In
explanation of this anomalous condition it is suggested that possibly
the larvae of lot 6 were better fitted for enduring and making the
best of hard conditions than were the individuals of lot 2, the
ancestors of the former lot having been selected two years ago
on a food-scarcity basis. This suggestion gathers support from an
inspection of the mortality notes, from which it appears that the
number of deaths for which the famine was probably a contributing
and not a primary cause in each lot which is for the first time
subjected to short rations is almost doubly greater than the num-
ber of deaths in lots which are descended from starved ancestors,
whether these ancestral famines occurred in successive or alternate
years. The figures indicate that a reduction of food is almost twice
as destructive upon the first generation which is subjected to it as
it is when visited on a second generation. Lot 4 follows lot 2 as
the seventh in rank and its position is in accord with the rule above
noted, its latest ancestral generation which enjoyed an optimum
amount of food during 1902 or 1903. Lot 8 holds lowest rank,
it and its ancestors having been subject to trying conditions through-
out the entire three years, during some one or two of which all
the other lots have enjoyed the best of food conditions. Thus it
appears that a generation of famine leaves its impression upon at
least the three generations which succeed it, yet the power of
recovery through generous feeding exhibited by the progeny of
individuals subjected to famine, is so extensive (witness lot 5)
that it appears probable that every trace left by the famine upon
the race would eventually disappear. It is even conceivable that the
ultimate result of the famine would be a strengthening of the race,
the famine having acted the part of a selective agent, preserving
only the strong.

"But although there is a large difference between the well fed
and the poorly fed, there persists, more obviously in late than in
early life, a very considerable discrepancy as to size among the



OTHER THEORIES OF SPECIES-FORMING. 301

individuals of each single lot whose environment, in so far as food,
temperature, room, humidity, etc., constitute it, is identical.

"For example, referring again to the weights at spinning time of
the larvae of 1903, it is true that, although each lot has a modal
class of weights to which the majority of its individuals belong and
about which the rest of the lot distributes itself rather symmetrically,
the extremes are surprisingly distant from one another. Thus in
lot i ,(th.e normal control lot) the extremes are 1,540 and 2,530
mg. ; in lot 2,* 800 and 1,402 mg. ; in lot 3, 1,180 and 2,170 mg. ;
in lot 4, 690 and 1,204 nig. ; in lot 5, 1,370 and 2,100 mg.

"That is to say, identical feeding has not made identical full-
grown larvae out of individuals which undoubtedly varied congeni-
tally at the start, those variations in embryo standing at birth in
the same relation to one another that they stand in the adults, hav-
ing merely been smaller and less readily discernible in early life,
although manifestly present in delicately measurable degree in the
earliest records made upon normal individuals. For example,
weight measurements taken immediately after the second moult,
range in one lot from 21 to 39 mg., or 60 per cent, of the modal
weight, while the weights in this same lot at spinning time, some
five weeks later, range from 534 to 2,080 mg., or 85 per cent, of
the mode for the lot. These embryonic but potentially large varia-
tions have simply 'grown up' along with the insect and are as truly
congenital in the adult as they were in the newly hatched larva.
This would seem to place quite conclusively in the category of
congenital variations some part of those variations (in size and pro-
portions of parts) which are commonly, and properly to some
degree, called acquired.

"That conditions of alimentation bear a directive relation to func-
tional activity, may be demonstrated by reference to the records of
the physiological functions of moulting, spinning, pupating, and
emerging, of the individuals of the experimental lots.

"An abnormal extension of the time needed for the metamor-
phosis follows upon a reduction of the food supply. The degree
of extension depends with the utmost nicety upon the amount of
food given the larvae. For example, among the 1901 generation of
silkworms, one control lot of twenty larvae was given the optimum
amount of food, a second lot of twenty larvae one-half this amount,
and a third lot of twenty larvae one-quarter of the amount. To
take the time of the fourth moulting as an illustration, the moulting
was begun by the first lot, which led the way by two and a half
days, at the end of which the second lot began to moult, while

* See table, next page, for the history of each lot.



3 02



DARWINISM TO-DAY.



the third lot was twenty-four hours behind the second. All the
individuals of the first lot had finished moulting on April 20, all
of the second on April 24, while the moulting in the third lot con-
tinued until April 29.

"As in the matter of weight, this retarding of the functions, by
means of a reduced food supply, affects not only the immediate
generation which is subjected to the famine, but the lingering effects
of it may be traced in the progeny of the dwarfed individuals at
least unto the third generation, even though two years of plenty
follow the one year of famine. The conditions which obtain in
each lot of individuals of the 1903 generation at spinning time are
shown in the accompanying table, which is based upon polygons
erected to include all the individuals in each lot.







RANK OF 1903 LOTS AS TO PROMPTNESS




HISTORY OF LOTS


IN SPINNING.


Lot






When Two-thirds of Each Lot


Num-
ber.






were Spinning.




1901.

Grand-
parents.


IQ02.

Parents.


1903.


Earliest
Spinner.


Date.


In Order
of Rank.


Latest
Spinner.


2












s


5


May 12
!! * 5


4


I
4


3 - ..-


o


s


o


2




2


3


4





s


s


4


" 26


5


5


5


s





o


3


" *3


2


2


6. ...


s


o


s


6


" 29


6


7


7


s


s





6


" 22


3


5


8


s


s


s


7


' 30


7


6



"This period in the life of the silkworms is particularly advan-
tageous for consideration here, because it marks the completion
of the feeding, so that the individuals of under-fed ancestry have
been given the best chance to recover, while those subject to altered
food conditions, had had the benefit of the alteration during the
entire food-taking period of life.

"In the table. 'O' means optimum amount of food, and 'S' means
short rations. To the right of the history of the lots is a section
showing the rank of the lots as to the extreme time limits of the
spinning time (emphasised congenital differences again), with a
safer criterion, as to their relative promptness, in the column be-
tween the extremes a column of figures intended to show the rela-
tive promptness with which a two-thirds majority of the larvae



OTHER THEORIES OF SPECIES-FORMING. 303

in each lot arrives at the spinning time, this proportion being taken
to represent the typical condition for the lot. The order in which
the lots are arranged in this column corresponds in a general way
with that prevalent for the weights at spinning time, and the
generalisations indulged in there may, with few exceptions, be
applied here. The lots which were well fed during the 1903
generation are ahead of all of those given short rations in 1903,
whatever ancestry they may have had. Lot I leads here as in the
matter of weight. Lots 3 and 5 tie for second place, having held
second and third places in weight. Lots 2 and 4 stand in the
same relation to one another that they held as to weight. Con-
trary to the weight relation, lot $ follows lot 2 at the spinning a
fact which illustrates again the general rule that two generations
of famine are more disastrous than one, but does not lend support
to the notion of natural selection on a food scarcity basis as pre-
viously suggested. Lot 8, which has had no relief from famine
during the entire three years, brings up the rear at the spinning,
as might be expected.

"This check upon functional activity exercised by diminished nour-
ishment affects the moulting, the time for the commencement of
spinning, and the issuing time for the adults, but the time spent
in the spinning of the cocoon, from its beginnings in the threads
of the supporting net to its apparent completion when the cocoon
becomes opaque, is practically identical for under-fed and well-
fed individuals. A reason for this exception to the tardy habits
of the under-fed is to be found in the fact that the under-fed
larvae produce less silk (less in size, thickness, and weight) than the
well-fed, thus accomplishing more meager results in the same
amount of time. That the individuals sentenced to short rations
should produce less silk than their well-fed neighbours is certainly
to be expected, silk not being made without leaves any more
readily than bricks without straw.

"Not only do short rations protract the time appointed for the
spinning, moulting, etc., but they appear to have a more striking
effect upon the actual occurrence of the moulting. The normal
number of moults for the silkworm larva is four. Five moults
have occurred for most of the individuals belonging to the under-
fed lots of 1902 and 1903, whereas none of the well-fed individuals
has undergone a fifth moult. It would seem, therefore, that the
occurrence of a fifth moult may be fairly ascribed to a reduction of
food; at least a fifth moult very frequently accompanies it and has
suggested the possibility that the enforced fasting of the under-
fed larva in the intervals between meals may have the same
physiological effect as the normal fasting which precedes the normal



3 o 4 DARWINISM TO-DAY.

moulting, during which time the so-called 'moulting fluid' is
secreted. That this effect may accumulate throughout the life-
time of the larva until the larva is actually forced to indulge in the
extravagance (of strength, feeding time, and body wall material)
of an additional moult is conceivable and will justify a further
test.

"As to the life-and-death selection due to famine, it may be
said, in addition to the previous discussion of mortality among
the experimental silkworms, that while lots subjected to two years
of famine (themselves in one year, their parents in the year before)
were fertile in so far as number of young hatched is concerned, it
was found to be exceedingly difficult to rear from them a 1903
generation. Indeed, at the time of the second moulting there were
but nineteen individuals (and tolerably vigorous larvae they were)
alive in the lot which had experienced two years of famine, al-
though every individual of the 149 hatched was carefully preserved
and royally fed a fact which goes to prove that the equipment at
birth of many of these larvae was inadequate.

"The fact that some larvae of starved ancestry have exhibited a
superiority over their fellows, in surviving and recovering from
hard conditions, is testimony for the existence of individual varia-
tions which cannot be defined anatomically, and yet which serve as
'handles' for natural selective agents. Such variations might be
called physiological variations, since it seems that the surviving
larvae must be those which are in best trim physiologically. These
larvae are able to make the most of the food offered to them. If
competition were allowed, they would probably be the individuals
which would cover the area most rapidly, securing whatever food
there might be. But under our experimental conditions there was
no competition allowed and yet certain precocious individuals made
more grams of flesh and more yards of silk, than other larvae
furnished with the same amount of raw material under like con-
ditions ; that this was due to the possession by the former of certain
congenital qualities of adaptability can scarcely be doubted.

"As to the fertility of the variously fed lots, in so far as number
of eggs produced is a measure of fertility, our records already
demonstrate the fact that the better nourished are the more fertile.
Furthermore, the economy in this matter practised by the starve-
lings is not merely numerical, quality as well as quantity of eggs
being affected. In witness of this point may be recalled the story
of the dying 1903 generation, produced from eggs of the starvelings
of 1901 and 1902, which would seem to offer conclusive evidence
that a famine suffered by the parents works its way into the germ-
cells so that most of their progeny have but a poor birthright."



OTHER THEORIES OF SPECIES-FORMING. 305

For special discussions of the inheritance of acquired characters,
see the following : Roth, E., "Die Thatsachen der Vererbung," 1885 ;
Ziegler, E., "Konnen erworbene pathologische Eigenschaften ver-
erbt werden und wie entstehen erbliche Krankheiten und Missbil-
dungen," 1886; Rohde, F., "Uber den gegenwartigen Stand der
Frage nach der Entstehung und Vererbung individuellen Eigen-
schaften und Krankheiten," 1896 ; Osborn, H. F., "Are Acquired
Variations Inherited," 1890; Elliott, D. G., "The Inheritance of
Acquired Characters," Auk, Vol. IX, pp. 77-104, 1892; Packard, A.
S., "On the Inheritance of Acquired Characters in Animals with
Complete Metamorphosis," Proc. Amer. Acad. Science, pp. 331-
370, 1894; Ritter, W. E., "On the Nature of Heredity and
Acquired Characters, and the Question of the Transmissibility of
these Characters," 1900; Wettstein, R. von, "Der Neo-Lamarckis-
mus und seine Beziehungen zum Darwinismus," 1903; Detto, Carl,
"Theorie der direkten Anpassung," 1904 (good bibliography of
papers on plant adaptations) ; Lendenfeld, R. V., "Variation and
Selection," Biol. Centralbl, Vol. XXIII, p. 489 ff., and p. 563 ff.,
1903; Pauly A., "Darwinismus und Lamarckismus," 1905; Lotsy,
J. P., "Vorlesungen uber Descendenztheorien," Vol. I, chap, xii,
1906; Wheeler, W. M., "The Polymorphism of Ants," Bull, of
Amer. Mus. Nat. Hist., Vol. XXIII, pp. 1-93, Plate I-VI, January,
1907 (see especially pp. 50-90). Certain writers of sociologic and
philosophic interests, have discussed especially the possibility of the
inheritance of acquired mental capacities or qualities in man ; ex-
pressing a belief in such inheritance are Buchner, "Die Macht der
Vererbung und ihr Einfluss auf der moralischen und geistigen
Fortschritt der Menschheit," 1882, and Hartmann, E. V., "Philo-
sophic des Unbewussten," loth ed. ; against such an inheritance is
Rawitz, B., "Urgeschichte, Geschichte, und Politik," 1903. Most
important of all the discussions of the inheritance of acquired char-
acters are those of Weismann, Spencer, and Eimer.

A recent American champion of Lamarckism is Caspar L. Red-
field, in whose writings ("Control of Heredity," 1903, "Evolution

Eedfield's of the Setter," in American Field, 1904 and 1905, and
position. "Breeding of the Trotter," in The Horseman, 1905)

is urged the doctrine that acquired mental and dynamic qualities are



Online LibraryVernon L. (Vernon Lyman) KelloggDarwinism to-day; a discussion of present-day scientific criticism of the Darwinian selection theories, together with a brief account of the principal other proposed auxilary and alternative theories of species-forming → online text (page 28 of 38)