In the history of biology, preformationism (or preformism) is the idea that organisms develop from miniature versions of themselves. Instead of assembly from parts, preformationists believe that the form of living things exist, in real terms, prior to their development. It suggests that all organisms were created at the same time, and that succeeding generations grow from homunculi that have existed since the beginning of creation.
Pythagoras 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.
The groundbreaking scientific insights provided by Galileo and Descartes seemed 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 (animalcules) in eggs and miniature plants in seeds.
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. This image, depicting what historian now refer to as the homunculus, has become iconic of the theory of preformationism. Hartsoeker 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.”
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.
Preformationism 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.