1. a person who believes in or advocates preformationism, the theory that organisms develop from miniature, fully-formed versions of themselves that exist from the beginning.
Usage: historical; biology

1. of, relating to, or characteristic of preformationism or preformationists.
Usage: historical; biology

Examples

• Seventeenth-century preformationists believed that a fully-formed human existed inside the egg or sperm.
• The preformationist theory was eventually disproven by advances in microscopy and embryology.
• Leeuwenhoek was among the early preformationists who thought they observed tiny humans in sperm cells.
• Preformationist ideas dominated biological thought until the epigenetic theory gained acceptance.
• Modern embryology has completely rejected preformationist explanations of development.