CHAPTER EIGHT

SEMANTIC BIOLOGY

A new wiew of life

Genetics was born in the first years of 1900 with the discovery that hereditary characters are carried by molecules which are physically present on chromosomes. These molecules of heredity – the genes – are responsible for the visible structures of the organisms but do not enter into those structures, which means that in every cell there are molecules which determine the characteristics of other molecules. In 1909, Wilhelm Johannsen concluded that this distinction is similar to the difference which exists between a project and its physical implementation, and represents therefore a dichotomy of the living world which is as deep as the Cartesian dichotomy between mind and body.
In order to distinguish the two types of molecules Johannsen called them genotype and phenotype, but such a dualism was almost universally rejected. At that time it was thought that proteins were responsible for both the visible structures and the hereditary characters, and all features seemed therefore reducible to a single type of molecules. The reality of the genotype-phenotype distinction was experimentally proved only in the 1940s and 50s, when molecular biology discovered that genes are chemically different from proteins, and, above all, when it became clear that genes carry linear information whereas proteins function through their three-dimensional structures.
The genotype-phenotype duality is therefore a dichotomy which divides non only two different biological functions (heredity and metabolism), but also two different physical quantities (information and energy). It is at the same time the most simple and the most general way of defining a living system, and has become the founding paradigm of modern biology, the scheme which has transformed the energy-based biology of the 19th century into the information-based biology of the 20th.