Cell Theory, Specificity and
Reproduction, 1837–1870
Staffan Müller-Wille
University of Exeter
[email protected]
What I am going to talk about ...
• Schwann‘s Cell Theory and the Idea of
Specificity
• Darwin‘s Theory of Pangenesis as a
Theory of Reproduction
• Mendel‘s Laws, Cell Theory, and
Specificity
• Semi-Autonomy and Modularity
1
The Cell as Unit of Life
• The cell is habitually addressed as the
structural, functional, and developmental
unit of life.
• Jan Sapp’s “three tenets” of cell theory:
– “all plants and animals are made of cells”
– “cells possess all the attributes of life
(assimilation, growth, reproduction)”
– “all cells arise from division of preexisting
cells” (Sapp, 2003, p. 75).
2
The Cell as Reproductive Unit of
Life
• All organisms run through life cycles, including a
single-cell stage of minimal life.
• Thinking in terms of life cycles and generations
was the crucial precondition for the emergence
of notions of biological inheritance in the midnineteenth century (Parnes, 2007).
• It ‘was not until the watershed period of the
1880s [that] cytological advances were brought
to bear directly on heredity’ (Churchill, 1987).
The late Arrival of the Cell
• It ‘was not until the watershed period of the
1880s [that] cytological advances were brought
to bear directly on heredity’ (Churchill, 1987).
• Cell theory a rather recent achievement of
biology; Edmund Beecher Wilson’s pivotal The
Cell in Development and Heredity (1896).
• Categories like whole/part, vitalism,
epigensis/preformation difficult to apply prior to
1900.
3
Johann Friedrich Blumenbach, “About
human races and pig races”, 1789
Pepsin
• ‘It emerges from my
experiments with artificial
digestion, that no single,
universal medium of
dissolution exists, but that
the materials that are
effective [in digestion] are
different for each different
foodstuff’
(Schwann, 1836)
4
Schwann 1838 (1847)
Schwann 1838 (1847)
5
Schwann 1838 (1847)
Schwann 1838 (1847)
6
Huxley‘s Critique of 1853
• Denies that the ‘primary histological
elements (cells) […] stand in the relation of
causes or centres to organization and the
“organizing force”’ – opens possibility of
transmutation (von Baer).
• Developmental differentiation of cells
results ‘from the operation of some
common determining power, apart from
them all’.
Schwann 1838 (1847)
7
Huxley‘s Critique of 1853
• ‘[T]he “vis essentialis” appears to have
essentially different and independent ends
in view – if we for the nonce speak
metaphorically’ (Huxley, 1853).
• Vitality ‘a “superadded” phenomenon,
acting externally on inherently inert matter’
or ‘a more immanent power, intimately
associated with organization’ (Sloan,
1986)
Any variation which is not inherited is unimportant for us. But
the number and diversity of inheritable deviations of structure,
both those of slight and those of considerable physiological
importance, is endless. Dr. Prosper Lucas's treatise, in two
large volumes, is the fullest and the best on this subject. No
breeder doubts how strong is the tendency to inheritance: like
produces like is his fundamental belief: doubts have been
thrown on this principle by theoretical writers alone. When a
deviation appears not unfrequently, and we see it in the father
and child, we cannot tell whether it may not be due to the
same original cause acting on both; but when amongst
individuals, apparently exposed to the same conditions, any
very rare deviation … appears in the parent … and it
reappears in the child, the mere doctrine of chances almost
compels us to attribute its reappearance to inheritance.
C. Darwin, The Origin of Species, 1859 (my emphasis)
8
Any variation which is not inherited is unimportant for us. But
the number and diversity of inheritable deviations of structure,
both those of slight and those of considerable physiological
importance, is endless. Dr. Prosper Lucas's treatise, in two
large volumes, is the fullest and the best on this subject. No
breeder doubts how strong is the tendency to inheritance: like
produces like is his fundamental belief: doubts have been
thrown on this principle by theoretical writers alone. When a
deviation appears not unfrequently, and we see it in the father
and child, we cannot tell whether it may not be due to the
same original cause acting on both; but when amongst
individuals, apparently exposed to the same conditions,
any very rare deviation … appears in the parent … and it
reappears in the child, the mere doctrine of chances almost
compels us to attribute its reappearance to inheritance.
C. Darwin, The Origin of Species, 1859 (my emphasis)
Every one would wish to explain to himself, even in
an imperfect manner, how it is possible for a
character possessed by some remote ancestor
suddenly to reappear in the offspring; how the effects
of increased or decreased use of a limb can be
transmitted to the child; how the male sexual element
can act not solely on the ovule, but occasionally on
the mother-form; how a limb can be reproduced on
the exact line of amputation, with neither too much
nor too little added; how the various modes of
reproduction are connected, and so forth. I am aware
that my view is merely a provisional hypothesis or
speculation; but until a better one be advanced, it
may be serviceable by bringing together a multitude
of facts which are at present left disconnected by any
efficient cause. As Whewell, the historian of the
inductive sciences, remarks:—"Hypotheses may
often be of service to science, when they involve a
certain portion of incompleteness, and even of error."
Under this point of view I venture to advance the
hypothesis of Pangenesis, which implies that the
whole organisation, in the sense of every separate
atom or unit, reproduces itself. Hence ovules and
pollen-grains,—the fertilised seed or egg, as well as
buds,—include and consist of a multitude of germs
thrown off from each separate atom of the organism.
C. Darwin, The variation of animals and plants under
domestication, v.2, 1868
9
Every one would wish to explain to himself, even in
an imperfect manner, how it is possible for a
character possessed by some remote ancestor
suddenly to reappear in the offspring; how the effects
of increased or decreased use of a limb can be
transmitted to the child; how the male sexual element
can act not solely on the ovule, but occasionally on
the mother-form; how a limb can be reproduced on
the exact line of amputation, with neither too much
nor too little added; how the various modes of
reproduction are connected, and so forth. I am aware
that my view is merely a provisional hypothesis or
speculation; but until a better one be advanced, it
may be serviceable by bringing together a multitude
of facts which are at present left disconnected by any
efficient cause. As Whewell, the historian of the
inductive sciences, remarks:—"Hypotheses may
often be of service to science, when they involve a
certain portion of incompleteness, and even of error."
Under this point of view I venture to advance the
hypothesis of Pangenesis, which implies that the
whole organisation, in the sense of every
separate atom or unit, reproduces itself. Hence
ovules and pollen-grains,—the fertilised seed or egg,
as well as buds,—include and consist of a multitude
of germs thrown off from each separate atom of the
organism.
C. Darwin, The variation of animals and plants under
domestication, v.2, 1868 (my emphasis)
This principle of Reversion is the most wonderful of
all the attributes of Inheritance. It proves to us that
the transmission of a character and its
development, which ordinarily go together and
thus escape discrimination, are distinct powers;
and these powers in some cases are even
antagonistic, for each acts alternately in successive
generations. Reversion is not a rare event,
depending on some unusual or favourable
combination of circumstances, but occurs so
regularly with crossed animals and plants, and so
frequently with uncrossed breeds, that it is evidently
an essential part of the principle of inheritance.
C. Darwin, The variation of animals and plants
under domestication, v.2, 1868
10
Physiologists agree that the whole organism
consists of a multitude of elemental parts, which
are to a great extent independent of each other.
Each organ, says Claude Bernard, has its proper life,
its autonomy; it can develop and reproduce itself
independently of the adjoining tissues. The great
German authority, Virchow, asserts still more
emphatically that each system, as the nervous or
osseous system, or the blood, consists of an
"enormous mass of minute centres of action...Every
element has its own special action, and even though
it derive its stimulus to activity from other parts, yet
alone effects the actual performance of its
duties...Every single epithelial and muscular fibre-cell
leads a sort of parasitical existence in relation to the
rest of the body...Every single bone-corpuscle really
possesses conditions of nutrition peculiar to itself."
C. Darwin, The variation of animals and plants under
domestication, v.2, 1868 (my emphasis)
Physiologists agree that the whole organism consists
of a multitude of elemental parts, which are to a great
extent independent of each other. Each organ, says
Claude Bernard, has its proper life, its autonomy; it
can develop and reproduce itself independently of the
adjoining tissues. The great German authority,
Virchow, asserts still more emphatically that each
system, as the nervous or osseous system, or the
blood, consists of an "enormous mass of minute
centres of action...Every element has its own
special action, and even though it derive its stimulus
to activity from other parts, yet alone effects the
actual performance of its duties...Every single
epithelial and muscular fibre-cell leads a sort of
parasitical existence in relation to the rest of the
body...Every single bone-corpuscle really possesses
conditions of nutrition peculiar to itself."
C. Darwin, The variation of animals and plants under
domestication, v.2, 1868 (my emphasis)
11
Rudolf Virchow, „Der Staat und die Ärzte“, 1849
•
The organism is “a kind of societal institution, an institution of a social kind”
•
But: “The State will certainly never be an organism, but only a complex of
organisms. The so-called state organism thrives best, where the
development of the individual is most guranteed.“
Whether each of the innumerable autonomous
elements of the body is a cell or the modified product
of a cell is a more doubtful question, even if so wide a
definition be given to the term, as to include cell-like
bodies without walls and without nucleus. … But
when an organism undergoes a great change of
structure during development, the cells, which at
each stage are supposed to be directly derived from
previously-existing cells must likewise be greatly
changed in nature; this change is apparently
attributed by the supporters of cellular doctrine to
some inherent power which the cells possess,
and not to any external agency.”
C. Darwin, The variation of animals and plants under
domestication, v.2, 1868 (my emphasis)
12
‘It is almost universally admitted that cells, or the
units of the body, propagate themselves by selfdivision or proliferation, retaining the same nature,
and ultimately becoming converted into the various
tissues and substances of the body. But besides this
means of increase I assume that cells, before their
conversion into completely passive or “formed
material”, throw off minute granules or atoms, which
circulate freely through the system, and when
supplied with proper nutriment multiply by selfdivision, subsequently becoming cells like those from
which they derived’
C. Darwin, The variation of animals and plants under
domestication, v.2, 1868 (my emphasis)
‘Turning now to Inheritance: if we suppose a
gelatinuous, homogenous Protozoon to vary and
assume a reddish colour, a minute separated atom
would naturally, as it grew to full size, retain the same
size; and we should have the simplest form of
inheritance’ ’
C. Darwin, The variation of animals and plants under
domestication, v.2, 1868 (my emphasis)
13
The fertilised germ of one of the higher animals,
subjected as it is to so vast a series of changes
from the germinal cell to old age,—incessantly
agitated by what Quatrefages well calls the
tourbillon vital,—is perhaps the most wonderful
object in nature. It is probable that hardly a change
of any kind affects either parent, without some mark
being left on the germ. But on the doctrine of
reversion, as given in this chapter, the germ
becomes a far more marvellous object, for, besides
the visible changes to which it is subjected, we
must believe that it is crowded with invisible
characters, proper to both sexes, to both the right
and left side of the body, and to a long line of male
and female ancestors separated by hundreds or
even thousands of generations from the present
time; and these characters, like those written on
paper with invisible ink, all lie ready to be evolved
under certain known or unknown conditions.
C. Darwin, The variation of animals and plants
under domestication, v.2, 1868
14
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