The logic of life : a history of heredity. The possible and the actual / François Jacob ; translated by Betty E. Spillmann.

  • François Jacob
Date:
1989
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Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: The logic of life : a history of heredity. The possible and the actual / François Jacob ; translated by Betty E. Spillmann. Source: Wellcome Collection.

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    mention a third one, biologists are no longer at ease. If molecular biology was able to develop so rapidly, this is largely because, in biology, information happens to be deter mined by simple linear sequences of building blocks, bases in nucleic acids and amino-acids in protein chains. Thus the genetic message, the relations between the primary structures, the logic of heredity, everything turned out to be one dimensional. Everything was simple. No wonder molecular biologists do not like to abandon this type of work, preferring instead to continue in the analysis of a one-dimensional world with protein and DNA sequencing. However, during the development of the embryo, the world is no longer merely linear. The one-dimensional se quence of bases in the genes determines in some way the production of two-dimensional cell layers that fold in a precise way to produce the three-dimensional tissues and organs that give the organism its shape, its properties and, as Seymour Benzer puts it, its four-dimensional behaviour. 11 How this occurs, however, is still a mystery. Biologists know in great detail the molecular anatomy of a human hand. They are completely ignorant of how the organism instructs itself to build that hand, what language it speaks to design a finger, what procedure it uses to sculpt a nail, how many genes are involved and how these genes interact. Development and cell differentiation can be viewed as involving a series of binary decisions, the outcome of each decision determining the possi bilities available for the following events. Sets of possibilities would thus be switched off at each fork. It is generally believed that such a process corresponds to a selective regulation of gene activity; but we do not even know the principles of the regulatory circuits that determine the number of cells, their distribution and movements, and the rates and direction of growth. We do not know the developmental tools of evolu tionary tinkering.
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