epigenesis

…in the proper environment; the epigenesis school believed that the egg is initially undifferentiated and that development occurs as a series of steps. Prominent supporters of the preformation doctrine, which was widely held until the 18th century, included Malpighi, Swammerdam, and Leeuwenhoek. In the 19th century, as criticism of preformation…

…was in line with his epigenetic idea—basic to embryology ever since—that development proceeds from simple to complex, from homogeneous to heterogeneous.

Epigenetics, the study of the chemical modification of genes and gene-associated proteins, has since offered an explanation for how certain traits developed during an organism’s lifetime can be passed along to its offspring.

Although this epigenetic process is now accepted as characterizing the general nature of development in both plants and animals, many questions remain to be solved. The French physician Marie François Xavier Bichat declared in 1801 that differentiating parts consist of various components called tissues; with the subsequent…

A notion that was widespread among pioneer biologists in the 18th century was that the fetus, and hence the adult organism that develops from it, is preformed in the sex cells. Some early microscopists even imagined that they saw a tiny homunculus, a diminutive…