-
1
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
-
2
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 preexistingcells” (Sapp,
2003, p. 75).
-
3
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 mid-nineteenth 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.
-
4
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)
-
5
Schwann 1838 (1847)
Schwann 1838 (1847)
-
6
Schwann 1838 (1847)
Schwann 1838 (1847)
-
7
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)
-
8
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)
-
9
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
-
10
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
-
11
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)
-
12
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)
-
13
‘It is almost universally admitted that cells, or the units of
the body, propagate themselves by self-division 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 self-division,
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)
-
14
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
-
15
-
16