What is this thing called ‘Life?’ One popular game in the relevant area of philosophy is to provide robust counter examples, which reveal failures in operational definitions of life. Failed attempts include physiological, metabolic, biochemical, genetic and thermodynamic definitions of life, all of which face problems. For example, a metabolic definition finds it hard to exclude fire (which grows and reproduces via chemical reactions), a biochemical definition does not exclude enzymes (which are biologically functional but not living systems), while a thermodynamic definition does not exclude mineral crystals (which create and sustain local order and may reproduce).
Erwin Schr?¶dinger, who dabbled in biology and philosophy by presenting a series of lectures on negentropy and molecular information, reduced the challenges of defining life to a much simpler series of principles. He inquired whether life is based on the laws of physics, because the construction and function of living matter may require a new level of description.
As Schr?¶dinger observed, the theoretical physicist deals with statistical approximations of matter and energy, but at such massive numbers of electrons and protons that variation and uniqueness among them appears canceled out. Not so with the biologist, who deals with molecules of far, far greater diversity. How do organisms cope with such apparent chaos, and how do they transmit that organization with such high fidelity, from generation to generation?
In What is Life?, Schr?¶dinger introduced the idea of an “aperiodic crystal” that contained genetic information in its configuration of covalent chemical bonds. In the 1950′s this idea both stimulated enthusiasm for discovering the genetic molecule and could be seen (in retrospect) as having been a well-reasoned theoretical prediction of what biologists should have been looking for during their search for the genetic material. Francis Crick attributed his interest in DNA to having read this book.
What is necessary for a reading of What is Life?, and indeed any understanding of molecular biology, is recognition of how biology transcends the physical realm. Yes, biology operates according to the laws of physics, but physics alone cannot recapitulate life. Ernst Mayr, in What Makes Biology Unique describes the autonomy of biology in much the same sense. That is, new phenomenon emerge in living organisms that could never be anticipated by physics alone. Or at least not until we understand life and its emergent properties better.
And no one has better described these aspects of life than Schr?¶dinger, to my knowledge, in the sixty-four years since the book was published.