The Theories
Pangenesis
In 1868 Charles Darwin proposed Pangenesis, a developmental theory of heredity. He suggested that all cells in an organism are capable of shedding minute particles he called gemmules, which are able to circulate throughout the body and finally congregate in the gonads. These particles are then transmitted to the next generation and are responsible for the transmission of characteristics from parent to offspring. If any cells of the parent undergo changes as a result of environmental change, they will consequently transmit modified gemmules to their offspring. Soon after Darwin's pangenetic theory was published, Francis Galton designed a series of blood transfusion experiments on differently pigmented rabbits to test its validity. He found no evidence in support of the existence of Darwin's gemmules and the concept of Pangenesis was largely abandoned.
Epigenetics
In the science of genetics, epigenetics is the study of cellular and physiological phenotypic trait variations that result from external or environmental factors that switch genes on and off and affect how cells express genes. Hence, epigenetic research seeks to describe dynamic alterations in the transcriptional potential of a cell. These alterations may or may not be heritable, although the use of the term epigenetic to describe processes that are not heritable is controversial. Unlike genetics based on changes to the DNA sequence (the genotype), the changes in gene expression or cellular phenotype of epigenetics have other causes, thus use of the prefix epi- (Greek: επί- over, outside of, around).
Vitalism
Vitalism is a theory that the characteristics and behaviors of life forms are expressed by a “vital force” and not biophysical means. Vitalism has a long history in medical philosophies – and it has ties to the four humors. It is sometimes referred to as a “life spark” and even as the soul. In the Eastern traditions it is essentially the same thing as “qi” or “chi”, which is heavily tied in to oriental medicinal methods.