In biology, epigenesis refers to the concept that organisms develop from cells. Organisms are made from spores and eggs that divide in many ways. Epigenesis produces a chain of events that leads to the development of the entire plant or animal. Each organism has a unique process of epigenesis but there are common steps that all organisms must undergo.
Genes are pieces of information used by the cell to control small cell changes. Cells use many genes all the time and some genes only a small amount of the time, this is called gene expression. Epigenesis uses gene expression as the main driving force behind cell differentiation, or cell changes. From the first cells of an organism, division causes cell differentiation and gene expression, which causes different types of cells to form.
Special cells, called stem cells, can change into different cell types depending on the environment the cell is in. Epigenesis is started by stem cells that come from the fertilized egg or spore. These first cell divisions produce stem cells that will use epigenesis to transform into billions of specific cell types.
Epigenesis is not simply a list of directions for the genetic program to build an organism with. The whole cell plays a role in gene expression with the use of special methods. Methylation, adding methane molecules to genes, is commonly used to suppress a gene, or turn it off. The environment also plays a key role in determining the gene expression because certain traits are only expressed under certain conditions. For example, working out produces more muscle cells because the workout lifestyle influences gene expression.
The ancient philosopher Aristotle was the first to document the process of epigenesis. He developed the idea from studying plants and animals, even though he had no access to modern tools. In his day, most people believed that god made everything. Aristotle fought this view and developed a surprisingly accurate model for the development process. He clearly understood that certain environmental factors would affect the growth process.
Modern biology has a good understanding of how organisms develop from conception. The process of gene expression and how it causes changes has been documented and studied at the molecular level. In 1939, Conrad Waddington defined epigenesis as the unfolding of the genetic program and this has led to many discoveries. The most startling is that the unfolding process is now related to many forms of cancer in humans.