EVIDENCE FROM MOLECULAR BIOLOGY

Mendel's four basic laws of genetics, formulated from meticulous experimentation, sparked a revolution in biology as they finally provided biologists with a rational basis to quantify observations and investigate cause–effect relationships.

To relate observed effects to the events that caused them is one of mankind's strong mental abilities. By understanding their relationship, it allows us to remember recurrent events and estimate their likelihood and reproducibility. This usually works well if a cause and its effect are linked by a short chain of events, but the challenge increases with complexity. Living organisms in their natural environment are probably the most complex entities to study, and causes and effects are not usually linked in single linear chains of causalities but rather in large multi-dimensional and interconnected meshworks.

It is interesting to note that at that time chemistry and, in particular, biochemistry were not yet ready to participate in this newly emerging field, which would later become known as molecular biology. The predominant understanding of chemistry was concentrated on other aspects; it had reached a new peak as a research field and everybody was convinced that the future belonged to chemistry. The main laws of mass action and thermodynamics were established and solidly anchored in every chemist. As biological macromolecules—nucleic acids and proteins—became the topic of investigation, molecular biology and biochemistry found a common denominator. Now, the biochemists stood whole-heartedly behind 'molecular biology', newly defined as the biochemistry related to DNA and its expression into proteinsand focused their collective experience on investigating how genetic information is stored, transmitted and translated into phenotypes. Biochemists had long learned to examine reactions by dividing them into the smallest individual steps in chemical terms. Under given conditions, such as pH, temperature and salt concentrations, these elementary steps are absolutely reproducible. Known as 'Descartes' clockwork', such a one-dimensional, linear chain of elementary steps leading from cause to effect was for a long time the basic understanding of technical and scientific processes, including biological ones. As the name indicates, Descartes used the mechanical clock as a model in which every cog induces the movement of the next in a reproducible and predictable way. This model is still applicable to the majority of biochemical reactions. This reductionist approach to molecular biology proved to be extremely successful initially and helped to unravel many of the basic molecular and cellular processes. However, some biologists started realizing quite early that the immense complexity of living organisms could not be explained solely on the basis of a clockwork mechanism.