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Cell Theory, Specificity and Reproduction, 1837–1870

Staffan Müller-Wille

University of Exeter

S.E.W.Mueller-Wille@exeter.ac.uk

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

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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).

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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.

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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)

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Schwann 1838 (1847)

Schwann 1838 (1847)

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Schwann 1838 (1847)

Schwann 1838 (1847)

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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)

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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)

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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

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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

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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)

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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)

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‘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)

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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

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