Preformationism

Preformationism is the theory that all organisms were created at the same time, and that succeeding generations grow from homunculi, animalcules, or other fully-formed but miniature versions of themselves that have existed since the beginning of creation.

In the case of humans, philosophers and theologians have conjectured that every individual existed as a homunculus in Adam's testicles (spermism) or Eve's ovaries (ovism).

Epigenesis, in contrast, is based on the idea 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) Magner, Lois. "A History of the Life Sciences". New York: Marcel Dekker, Inc, 2002]

Philosophical development

Pythagoras was one of the first to elaborate a theory of generation, the biological production of offspring. He advocated a patrocline theory whereas males contributed the essential characteristics of their offspring while females contributed only a material substrate. Pythagorus' theory heavily inspired Aristotle, who elaborated both upon preformation and epigenesis, two distinct theories of generation. Subsequent theorists such as Galen, Realdo Colombo and Girolamo Fabrici built upon Aristotle's theories, which were prevalent well into the 17th century.

In 1651 William Harvey published "On the Generation of Animals" ("De Generatione"), a seminal work on embryology that contradicted many of Aristotle's fundamental ideas on the matter. However, Harvey couldn't support his ideas on epigenesis with evidence of a convincing mechanism of generation because animal gametes were too small to be seen without a microscope, and hormones were unknown. Although Harvey 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 reformationist theories seemed to be compatible with natural philosophy at the time and to require less-radical hypotheses than epigenesis did.clarifyme Epigenesis also suffered from perceived disharmony with dominant Christian theology because it suggested that unorganized matter could generate life without the need for God's intervention.

The groundbreaking scientific insights provided by Galileo and Newton, and Cartesianism provided a mechanistic framework that seemed to support preformationism. Because of technological limitations, there was no available mechanical explanation for epigenesis. It was simpler and more convenient to postulate preformed miniature organisms that expanded in accordance with mechanical laws. Some naturalists claimed to actually see miniature preformed animals (animalcules) in eggs and miniature plants in seeds.The term homunculus was used in the discussion of conception and birth.

Elaboration of preformationism

After the discovery of spermatozoa 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)Friedman, David M. A Mind of Its Own: A Cultural History of the Penis. New York: The Free Press, 2001]

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 produced an image of tiny men inside the sperm, which he called "animalcule" or "homunculus."

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." [ Nicolas Malebranche, "De la recherche de la vérité" (The Search After Truth), book I, chapter VI, first section (1674-1675) ]

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. [Smith, Justin Erik. “Leibniz’s Preformationism: Between Metaphysics and Biology.”Analecta Husserliana, the Yearbook of Phenomenological Research. Volume LXXVII. (2002) 161-192.]

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.

Criticisms and cell theory

Caspar Friedrich Wolff, an epigenicist, was an 18th-century exception who argued for objectivity and freedom from religious influence on scientific questions Fact|date=September 2007.

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)Gee, Henry. Jacob’s Ladder: The History of the Human Genome. New York: W.W. Norton & Company, Inc, 2004]

References

* Clara Pinto Correia, "The Ovary of Eve: Egg and Sperm Preformation", Chicago: University of Chicago Press, 1997. ISBN 0-226-66952-1

See also

*Biogenesis

External links