Preformationism
Encyclopedia
In the history of biology
, preformationism (or preformism) is either the specific contention that all organism
s were created at the same time, and that succeeding generations grow from homunculi
, animalcule
s, or other fully formed but miniature versions of themselves that have existed since the beginning of creation, or, later and more generally, the notion (opposed to epigenesis
) that the form of living things in some sense preexists their development
.
Epigenesis
, then, in this context, is the denial of preformationism: the idea that, in some sense, the form of living things comes into existence. As opposed to "strict" preformationism, it is the notion that "each embryo or organism is gradually produced from an undifferentiated mass by a series of steps and stages during which new parts are added." (Magner 2002, p. 154) This word is still used, on the other hand, in a more modern sense, to refer to those aspects of the generation of form during ontogeny which are not strictly genetic; or, in other words, epigenetic
.
The historical ideas of preformationism and epigenesis, and the rivalry between them, are obviated by our contemporary understanding
of the genetic code
and its molecular basis
together with developmental biology
and epigenetics
.
is one of the earliest thinkers credited with ideas about the origin of form in the biological production of offspring. It is said that he originated "spermism", the doctrine that fathers contribute the essential characteristics of their offspring while mothers contribute only a material substrate. Aristotle
accepted and elaborated this idea, and his writings are the vector which transmitted it to later Europeans. Aristotle purported to analyse ontogeny in terms of the material, formal, efficient, and teleological causes (as they are usually named by later anglophone philosophy) – a view which, though more complex than some subsequent ones, is essentially more epigenetic than preformationist. Later, European physicians such as Galen
, Realdo Colombo
and Girolamo Fabrici would build upon Aristotle's theories, which were prevalent well into the 17th century.
In 1651 William Harvey
published On the Generation of Animals (Exercitationes de Generatione Animalium
), a seminal work on embryology
that contradicted many of Aristotle's fundamental ideas on the matter. Harvey famously asserted, for example, that ex ovo omnia--all animals come from eggs. Because of this assertion in particular, Harvey is often credited with being the father of ovist preformationism. However, Harvey's ideas about the process of development were fundamentally epigenesist. As gametes (male sperm and female ova) were too small to be seen under the best magnification at the time, Harvey's account of fertilization was theoretical rather than descriptive. Although he once postulated a "spiritous substance" that exerted its effect on the female body, he later rejected it as superfluous and thus unscientific. He guessed instead that fertilization occurred through a mysterious transference by contact, or contagion.
Harvey's epigenesis, more mechanistic and less vitalist than the Aristotelian version, was thus more compatible with the natural philosophy
of the time. Still, the idea that unorganized matter could ultimately self-organize into life challenged dominant Christian
theology of the time as well as the mechanistic
framework of Cartesianism
. Because of technological limitations, there was no available mechanical explanation for epigenesis. The groundbreaking scientific insights
provided by Galileo
and Descartes
seemed instead to support preformationism. It was simpler and more convenient to postulate preformed miniature organisms that expanded in accordance with mechanical laws. So convincing was this explanation that some naturalists claimed to actually see miniature preformed animals (animalcule
s) in eggs and miniature plants in seeds. In the case of humans, the term homunculus
was used.
in 1677 by Dutch microscopist Antonie van Leeuwenhoek, the epigenist theory proved more difficult to defend: how could complex organisms such as human beings develop from such simple organisms? Henceforth, Joseph de Aromatari, and then Marcello Malpighi
and Jan Swammerdam
made observations using microscopes in the late 17th century, and interpreted their findings to develop the preformationist theory. During two centuries, until the invention of cell theory
, preformationists would oppose epigenicists, and, inside the preformationist camp, spermists (who claimed the homonculus must come from the man) to ovists, who located the homonculus in the ova.
Dutch microscopist Antonie van Leeuwenhoek was one of the first to observe spermatozoa. He described the spermatozoa of about 30 species, and thought he saw in semen, "all manner of great and small vessels, so various and so numerous that I do not doubt that they be nerves, arteries and veins...And when I saw them, I felt convinced that, in no full grown body, are there any vessels which may not be found likewise in semen." (Friedman 76-7)
Leeuwenhoek discovered that the origin of semen was the testicles and was a committed preformationist and spermist. He reasoned that the movement of spermatozoa was evidence of animal life, which presumed a complex structure and, for human sperm, a soul. (Friedman 79)
In 1694, Nicolaas Hartsoeker, in his Essai de Dioptrique concerning things large and small that could be seen with optical lenses, produced an image of a tiny human form curled up inside the sperm, which he referred to in the French as petit l'infant and le petit animal. This image, depicting what historian now refer to as the homunculus
, has become iconic of the theory of preformationism, and appears in almost every textbook concerning the history of embryological science.
Philosopher Nicolas Malebranche
was the first to advance the hypothesis that each embryo could contain even smaller embryos ad infinitum
, like a Matryoshka doll
. According to Malebranche, "an infinite series of plants and animals were contained within the seed or the egg, but only naturalists with sufficient skill and experience could detect their presence." (Magner 158-9) In fact, Malebranche only alleged this, observing that if microscopes enabled us to see very little animals and plants, maybe even smaller creatures could exist. He claimed that it was not unreasonable to believe that "they are infinite trees in only one seed," as he stated that we could already see chicken in eggs, tulips in bulbs, frogs in eggs. From this, he hypothethized that "all the bodies of humans and animals," already born and yet to be born, "were perhaps produced as soon as the creation of the world."
Ova
were known in some non-mammalian species, and semen
was thought to spur the development of the preformed organism contained therein. The theory that located the homonculus in the egg was called ovism. But when spermatozoa were discovered, a rival camp of spermists sprang up, claiming that the homunculus must come from the male. In fact, the term "spermatozoon," coined by Karl Ernst von Baer
, means "seed animals."
With the discovery of sperm and the concept of spermism came a religious quandary. Why would so many little animals be wasted with each ejaculation of semen? Pierre Lyonet said the wastage proved that sperm couldn't be the seeds of life. Leibniz supported a theory called panspermism that the wasted sperm might actually be scattered (for example, by the wind) and generate life wherever they found a suitable host.
Leibniz also believed that “death is only a transformation enveloped through diminution,” meaning that not only have organisms always existed in their living form, but that they will always exist, body united to soul, even past apparent death.
In the 18th century, some animalculists thought that an animal's sperm behaved like the adult animal, and recorded such observations. Some, but not all, preformationists at this time claimed to see miniature organisms inside the sex cells. But about this time, spermists began to use more abstract arguments to support their theories.
Jean Astruc
, noting that parents of both sexes seemed to influence the characteristics of their offspring, suggested that the animalcule came from the sperm and was then shaped as it passed into the egg. Buffon and Pierre Louis Moreau also advocated theories to explain this phenomenon.
Preformationism, especially ovism, was the dominant theory of generation during the 18th century. It competed with spontaneous generation
and epigenesis
, but those two theories were often rejected on the grounds that inert matter could not produce life without God's intervention.
Some animals' regeneration
capabilities challenged preformationism, and Abraham Trembley
's studies of the hydra
convinced various authorities to reject their former views.
Lazaro Spallanzani experimented with regeneration and semen, but failed to discern the importance of spermatozoa, dismissing them as parasitic worms and concluding instead that it was the liquid portion of semen that caused the preformed organism in the ovum
to develop.
, an epigenicist, was an 18th-century exception who argued for objectivity and freedom from religious influence on scientific questions .
Despite careful observation of developing embryos, epigenesis suffered from a lack of a theoretical mechanism of generation. Wolff proposed an "essential force" as the agent of change, and Immanuel Kant
with Johann Friedrich Blumenbach
proposed a "developing drive" or Bildungstrieb, a concept related to self-organization
.
Naturalists of the late 18th century and the 19th century embraced Wolff's philosophy, but primarily because they rejected the application of mechanistic development, as seen in the expansion of miniature organisms. It wasn't until the late 19th century that preformationism was discarded in the face of cell theory
. Now scientists "realized that they need not treat living organisms as machines, nor give up all hope of ever explaining the mechanisms that govern living beings." (Magner 173)
When John Dalton
's atomic theory
of matter superseded Descartes' philosophy of infinite divisibility
at the beginning of the 19th century, preformationism was struck a further blow. There simply wasn't enough space at the bottom of the spectrum to accommodate infinitely stacked animalcules, without bumping into the constituent parts of matter. (Gee 43)
History of biology
The history of biology traces the study of the living world from ancient to modern times. Although the concept of biology as a single coherent field arose in the 19th century, the biological sciences emerged from traditions of medicine and natural history reaching back to ayurveda, ancient Egyptian...
, preformationism (or preformism) is either the specific contention that all organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s were created at the same time, and that succeeding generations grow from homunculi
Homunculus
Homunculus is a term used, generally, in various fields of study to refer to any representation of a human being. Historically, it referred specifically to the concept of a miniature though fully formed human body, for example, in the studies of alchemy and preformationism...
, animalcule
Animalcule
Animalcule is an older term for a microscopic animal or protozoan. Some better-known animalcules include:* Actinophrys, and other heliozoa, called sun animalcules...
s, or other fully formed but miniature versions of themselves that have existed since the beginning of creation, or, later and more generally, the notion (opposed to epigenesis
Epigenesis
Epigenesis may refer to:* Epigenesis , describes morphogenesis and development of an organism* By analogy, a philosophical and theological concept, part of the concept of spiritual evolution* The Epigenesis, a 2010 album by Melechesh...
) that the form of living things in some sense preexists their development
Ontogeny
Ontogeny is the origin and the development of an organism – for example: from the fertilized egg to mature form. It covers in essence, the study of an organism's lifespan...
.
Epigenesis
Epigenesis
Epigenesis may refer to:* Epigenesis , describes morphogenesis and development of an organism* By analogy, a philosophical and theological concept, part of the concept of spiritual evolution* The Epigenesis, a 2010 album by Melechesh...
, then, in this context, is the denial of preformationism: the idea that, in some sense, the form of living things comes into existence. As opposed to "strict" preformationism, it is the notion that "each embryo or organism is gradually produced from an undifferentiated mass by a series of steps and stages during which new parts are added." (Magner 2002, p. 154) This word is still used, on the other hand, in a more modern sense, to refer to those aspects of the generation of form during ontogeny which are not strictly genetic; or, in other words, epigenetic
Epigenetics
In biology, and specifically genetics, epigenetics is the study of heritable changes in gene expression or cellular phenotype caused by mechanisms other than changes in the underlying DNA sequence – hence the name epi- -genetics...
.
The historical ideas of preformationism and epigenesis, and the rivalry between them, are obviated by our contemporary understanding
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
of the genetic code
Genetic code
The genetic code is the set of rules by which information encoded in genetic material is translated into proteins by living cells....
and its molecular basis
Nucleic acid
Nucleic acids are biological molecules essential for life, and include DNA and RNA . Together with proteins, nucleic acids make up the most important macromolecules; each is found in abundance in all living things, where they function in encoding, transmitting and expressing genetic information...
together with developmental biology
Developmental biology
Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis", which is the process that gives rise to tissues, organs and anatomy.- Related fields of study...
and epigenetics
Epigenetics
In biology, and specifically genetics, epigenetics is the study of heritable changes in gene expression or cellular phenotype caused by mechanisms other than changes in the underlying DNA sequence – hence the name epi- -genetics...
.
Philosophical development
PythagorasPythagoras
Pythagoras of Samos was an Ionian Greek philosopher, mathematician, and founder of the religious movement called Pythagoreanism. Most of the information about Pythagoras was written down centuries after he lived, so very little reliable information is known about him...
is one of the earliest thinkers credited with ideas about the origin of form in the biological production of offspring. It is said that he originated "spermism", the doctrine that fathers contribute the essential characteristics of their offspring while mothers contribute only a material substrate. Aristotle
Aristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...
accepted and elaborated this idea, and his writings are the vector which transmitted it to later Europeans. Aristotle purported to analyse ontogeny in terms of the material, formal, efficient, and teleological causes (as they are usually named by later anglophone philosophy) – a view which, though more complex than some subsequent ones, is essentially more epigenetic than preformationist. Later, European physicians such as Galen
Galen
Aelius Galenus or Claudius Galenus , better known as Galen of Pergamon , was a prominent Roman physician, surgeon and philosopher...
, Realdo Colombo
Realdo Colombo
Realdo Colombo was an Italian professor of anatomy and a surgeon at the University of Padua between 1544 and 1559.- Early life and education :Matteo Realdo Colombo or Renaldus Columbus, was born in Cremona, Lombardy to an apothecary named Antonio Colombo...
and Girolamo Fabrici would build upon Aristotle's theories, which were prevalent well into the 17th century.
In 1651 William Harvey
William Harvey
William Harvey was an English physician who was the first person to describe completely and in detail the systemic circulation and properties of blood being pumped to the body by the heart...
published On the Generation of Animals (Exercitationes de Generatione Animalium
William Harvey
William Harvey was an English physician who was the first person to describe completely and in detail the systemic circulation and properties of blood being pumped to the body by the heart...
), a seminal work on embryology
Embryology
Embryology is a science which is about the development of an embryo from the fertilization of the ovum to the fetus stage...
that contradicted many of Aristotle's fundamental ideas on the matter. Harvey famously asserted, for example, that ex ovo omnia--all animals come from eggs. Because of this assertion in particular, Harvey is often credited with being the father of ovist preformationism. However, Harvey's ideas about the process of development were fundamentally epigenesist. As gametes (male sperm and female ova) were too small to be seen under the best magnification at the time, Harvey's account of fertilization was theoretical rather than descriptive. Although he once postulated a "spiritous substance" that exerted its effect on the female body, he later rejected it as superfluous and thus unscientific. He guessed instead that fertilization occurred through a mysterious transference by contact, or contagion.
Harvey's epigenesis, more mechanistic and less vitalist than the Aristotelian version, was thus more compatible with the natural philosophy
Natural philosophy
Natural philosophy or the philosophy of nature , is a term applied to the study of nature and the physical universe that was dominant before the development of modern science...
of the time. Still, the idea that unorganized matter could ultimately self-organize into life challenged dominant Christian
Christian
A Christian is a person who adheres to Christianity, an Abrahamic, monotheistic religion based on the life and teachings of Jesus of Nazareth as recorded in the Canonical gospels and the letters of the New Testament...
theology of the time as well as the mechanistic
Mechanism (philosophy)
Mechanism is the belief that natural wholes are like machines or artifacts, composed of parts lacking any intrinsic relationship to each other, and with their order imposed from without. Thus, the source of an apparent thing's activities is not the whole itself, but its parts or an external...
framework of Cartesianism
Cartesianism
Cartesian means of or relating to the French philosopher and mathematician René Descartes—from his name—Rene Des-Cartes. It may refer to:*Cartesian anxiety*Cartesian circle*Cartesian dualism...
. Because of technological limitations, there was no available mechanical explanation for epigenesis. The groundbreaking scientific insights
Scientific revolution
The Scientific Revolution is an era associated primarily with the 16th and 17th centuries during which new ideas and knowledge in physics, astronomy, biology, medicine and chemistry transformed medieval and ancient views of nature and laid the foundations for modern science...
provided by Galileo
Galileo Galilei
Galileo Galilei , was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations and support for Copernicanism...
and Descartes
René Descartes
René Descartes ; was a French philosopher and writer who spent most of his adult life in the Dutch Republic. He has been dubbed the 'Father of Modern Philosophy', and much subsequent Western philosophy is a response to his writings, which are studied closely to this day...
seemed instead to support preformationism. It was simpler and more convenient to postulate preformed miniature organisms that expanded in accordance with mechanical laws. So convincing was this explanation that some naturalists claimed to actually see miniature preformed animals (animalcule
Animalcule
Animalcule is an older term for a microscopic animal or protozoan. Some better-known animalcules include:* Actinophrys, and other heliozoa, called sun animalcules...
s) in eggs and miniature plants in seeds. In the case of humans, the term homunculus
Homunculus
Homunculus is a term used, generally, in various fields of study to refer to any representation of a human being. Historically, it referred specifically to the concept of a miniature though fully formed human body, for example, in the studies of alchemy and preformationism...
was used.
Elaboration of preformationism
After the discovery of spermatozoaSpermatozoon
A spermatozoon is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote...
in 1677 by Dutch microscopist Antonie van Leeuwenhoek, the epigenist theory proved more difficult to defend: how could complex organisms such as human beings develop from such simple organisms? Henceforth, Joseph de Aromatari, and then Marcello Malpighi
Marcello Malpighi
Marcello Malpighi was an Italian doctor, who gave his name to several physiological features, like the Malpighian tubule system.-Early years:...
and Jan Swammerdam
Jan Swammerdam
Jan Swammerdam was a Dutch biologist and microscopist. His work on insects demonstrated that the various phases during the life of an insect—egg, larva, pupa, and adult—are different forms of the same animal. As part of his anatomical research, he carried out experiments on muscle contraction...
made observations using microscopes in the late 17th century, and interpreted their findings to develop the preformationist theory. During two centuries, until the invention of cell theory
Cell theory
Cell theory refers to the idea that cells are the basic unit of structure in every living thing. Development of this theory during the mid 17th century was made possible by advances in microscopy. This theory is one of the foundations of biology...
, preformationists would oppose epigenicists, and, inside the preformationist camp, spermists (who claimed the homonculus must come from the man) to ovists, who located the homonculus in the ova.
Dutch microscopist Antonie van Leeuwenhoek was one of the first to observe spermatozoa. He described the spermatozoa of about 30 species, and thought he saw in semen, "all manner of great and small vessels, so various and so numerous that I do not doubt that they be nerves, arteries and veins...And when I saw them, I felt convinced that, in no full grown body, are there any vessels which may not be found likewise in semen." (Friedman 76-7)
Leeuwenhoek discovered that the origin of semen was the testicles and was a committed preformationist and spermist. He reasoned that the movement of spermatozoa was evidence of animal life, which presumed a complex structure and, for human sperm, a soul. (Friedman 79)
In 1694, Nicolaas Hartsoeker, in his Essai de Dioptrique concerning things large and small that could be seen with optical lenses, produced an image of a tiny human form curled up inside the sperm, which he referred to in the French as petit l'infant and le petit animal. This image, depicting what historian now refer to as the homunculus
Homunculus
Homunculus is a term used, generally, in various fields of study to refer to any representation of a human being. Historically, it referred specifically to the concept of a miniature though fully formed human body, for example, in the studies of alchemy and preformationism...
, has become iconic of the theory of preformationism, and appears in almost every textbook concerning the history of embryological science.
Philosopher Nicolas Malebranche
Nicolas Malebranche
Nicolas Malebranche ; was a French Oratorian and rationalist philosopher. In his works, he sought to synthesize the thought of St. Augustine and Descartes, in order to demonstrate the active role of God in every aspect of the world...
was the first to advance the hypothesis that each embryo could contain even smaller embryos ad infinitum
Ad infinitum
Ad infinitum is a Latin phrase meaning "to infinity."In context, it usually means "continue forever, without limit" and thus can be used to describe a non-terminating process, a non-terminating repeating process, or a set of instructions to be repeated "forever," among other uses...
, like a Matryoshka doll
Matryoshka doll
A matryoshka doll is a Russian nesting doll which is a set of wooden dolls of decreasing size placed one inside the other. The first Russian nested doll set was carved in 1890 by Vasily Zvyozdochkin from a design by Sergey Malyutin, who was a folk crafts painter at Abramtsevo...
. According to Malebranche, "an infinite series of plants and animals were contained within the seed or the egg, but only naturalists with sufficient skill and experience could detect their presence." (Magner 158-9) In fact, Malebranche only alleged this, observing that if microscopes enabled us to see very little animals and plants, maybe even smaller creatures could exist. He claimed that it was not unreasonable to believe that "they are infinite trees in only one seed," as he stated that we could already see chicken in eggs, tulips in bulbs, frogs in eggs. From this, he hypothethized that "all the bodies of humans and animals," already born and yet to be born, "were perhaps produced as soon as the creation of the world."
Ova
Ovum
An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization...
were known in some non-mammalian species, and semen
Semen
Semen is an organic fluid, also known as seminal fluid, that may contain spermatozoa. It is secreted by the gonads and other sexual organs of male or hermaphroditic animals and can fertilize female ova...
was thought to spur the development of the preformed organism contained therein. The theory that located the homonculus in the egg was called ovism. But when spermatozoa were discovered, a rival camp of spermists sprang up, claiming that the homunculus must come from the male. In fact, the term "spermatozoon," coined by Karl Ernst von Baer
Karl Ernst von Baer
Karl Ernst Ritter von Baer, Edler von Huthorn also known in Russia as Karl Maksimovich Baer was an Estonian naturalist, biologist, geologist, meteorologist, geographer, a founding father of embryology, explorer of European Russia and Scandinavia, a member of the Russian Academy of Sciences, a...
, means "seed animals."
With the discovery of sperm and the concept of spermism came a religious quandary. Why would so many little animals be wasted with each ejaculation of semen? Pierre Lyonet said the wastage proved that sperm couldn't be the seeds of life. Leibniz supported a theory called panspermism that the wasted sperm might actually be scattered (for example, by the wind) and generate life wherever they found a suitable host.
Leibniz also believed that “death is only a transformation enveloped through diminution,” meaning that not only have organisms always existed in their living form, but that they will always exist, body united to soul, even past apparent death.
In the 18th century, some animalculists thought that an animal's sperm behaved like the adult animal, and recorded such observations. Some, but not all, preformationists at this time claimed to see miniature organisms inside the sex cells. But about this time, spermists began to use more abstract arguments to support their theories.
Jean Astruc
Jean Astruc
Jean Astruc was a professor of medicine at Montpellier and Paris, who wrote the first great treatise on syphilis and venereal diseases, and also, with a small anonymously published book, played a fundamental part in the origins of critical textual analysis of works of scripture...
, noting that parents of both sexes seemed to influence the characteristics of their offspring, suggested that the animalcule came from the sperm and was then shaped as it passed into the egg. Buffon and Pierre Louis Moreau also advocated theories to explain this phenomenon.
Preformationism, especially ovism, was the dominant theory of generation during the 18th century. It competed with spontaneous generation
Spontaneous generation
Spontaneous generation or Equivocal generation is an obsolete principle regarding the origin of life from inanimate matter, which held that this process was a commonplace and everyday occurrence, as distinguished from univocal generation, or reproduction from parent...
and epigenesis
Epigenesis
Epigenesis may refer to:* Epigenesis , describes morphogenesis and development of an organism* By analogy, a philosophical and theological concept, part of the concept of spiritual evolution* The Epigenesis, a 2010 album by Melechesh...
, but those two theories were often rejected on the grounds that inert matter could not produce life without God's intervention.
Some animals' regeneration
Regeneration (biology)
In biology, regeneration is the process of renewal, restoration, and growth that makes genomes, cells, organs, organisms, and ecosystems resilient to natural fluctuations or events that cause disturbance or damage. Every species is capable of regeneration, from bacteria to humans. At its most...
capabilities challenged preformationism, and Abraham Trembley
Abraham Trembley
Abraham Trembley was a Swiss naturalist. He is best known for being the first to study freshwater polyps or hydra and for being among the first to develop experimental zoology...
's studies of the hydra
Hydra (genus)
Hydra is a genus of simple fresh-water animal possessing radial symmetry. Hydras are predatory animals belonging to the phylum Cnidaria and the class Hydrozoa. They can be found in most unpolluted fresh-water ponds, lakes, and streams in the temperate and tropical regions and can be found by...
convinced various authorities to reject their former views.
Lazaro Spallanzani experimented with regeneration and semen, but failed to discern the importance of spermatozoa, dismissing them as parasitic worms and concluding instead that it was the liquid portion of semen that caused the preformed organism in the ovum
Ovum
An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization...
to develop.
Criticisms and cell theory
Caspar Friedrich WolffCaspar Friedrich Wolff
Caspar Friedrich Wolff was a German physiologist and one of the founders of embryology.-Life:Wolff was born in Berlin, Brandenburg. In 1230 he graduated as an M.D...
, an epigenicist, was an 18th-century exception who argued for objectivity and freedom from religious influence on scientific questions .
Despite careful observation of developing embryos, epigenesis suffered from a lack of a theoretical mechanism of generation. Wolff proposed an "essential force" as the agent of change, and Immanuel Kant
Immanuel Kant
Immanuel Kant was a German philosopher from Königsberg , researching, lecturing and writing on philosophy and anthropology at the end of the 18th Century Enlightenment....
with Johann Friedrich Blumenbach
Johann Friedrich Blumenbach
Johann Friedrich Blumenbach was a German physician, physiologist and anthropologist, one of the first to explore the study of mankind as an aspect of natural history, whose teachings in comparative anatomy were applied to classification of what he called human races, of which he determined...
proposed a "developing drive" or Bildungstrieb, a concept related to self-organization
Self-organization
Self-organization is the process where a structure or pattern appears in a system without a central authority or external element imposing it through planning...
.
Naturalists of the late 18th century and the 19th century embraced Wolff's philosophy, but primarily because they rejected the application of mechanistic development, as seen in the expansion of miniature organisms. It wasn't until the late 19th century that preformationism was discarded in the face of cell theory
Cell theory
Cell theory refers to the idea that cells are the basic unit of structure in every living thing. Development of this theory during the mid 17th century was made possible by advances in microscopy. This theory is one of the foundations of biology...
. Now scientists "realized that they need not treat living organisms as machines, nor give up all hope of ever explaining the mechanisms that govern living beings." (Magner 173)
When John Dalton
John Dalton
John Dalton FRS was an English chemist, meteorologist and physicist. He is best known for his pioneering work in the development of modern atomic theory, and his research into colour blindness .-Early life:John Dalton was born into a Quaker family at Eaglesfield, near Cockermouth, Cumberland,...
's atomic theory
Atomic theory
In chemistry and physics, atomic theory is a theory of the nature of matter, which states that matter is composed of discrete units called atoms, as opposed to the obsolete notion that matter could be divided into any arbitrarily small quantity...
of matter superseded Descartes' philosophy of infinite divisibility
Infinite divisibility
The concept of infinite divisibility arises in different ways in philosophy, physics, economics, order theory , and probability theory...
at the beginning of the 19th century, preformationism was struck a further blow. There simply wasn't enough space at the bottom of the spectrum to accommodate infinitely stacked animalcules, without bumping into the constituent parts of matter. (Gee 43)