An Astronaut’s Dilemma 11“9x6” b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity(7) Life is a system capable of mutation and variations in succeeding
generations (genetic definition).
(8) Life is a system capable of creating order out of disorder (thermo-
dynamic definition).
(9) Life is a network of information systems (cybernetic definition).
And then there is the “seven-pillar” definition of life, also known as
“PICERAS”, an acronym for: program, improvisation, compartmental-
ization, energy, regeneration, adaptability, and seclusion.^3
There is also a thoughtful definition given by Perret in 1952, which
says: “Life is a potentially self-perpetuating system of linked organic
reactions, catalyzed stepwise and almost isothermally by complex and
specific organic catalysts which are themselves produced by the system.”^4
No doubt, the above definitions and descriptions all fit life observed
on Earth. But what about other forms of life that might exist in other
parts of the universe? They could be drastically different. For example,
they might derive their energy source not from sunlight but from other
thermodynamic systems. They might be based on silicon rather than
carbon. They might use arsenic rather than phosphorus. They might
have a hydrogen-bond rather than covalent-bond backbone. They might
thrive in high pressure/temperature, or in very acidic or alkaline condi-
tions. They might have a metabolism based on an organic solvent other
than water. They might even exist entirely in solid or gaseous form. Or,
they might have an entirely different genetic system.^5
To accommodate all the possibilities of life, on Earth and else-
where, here is a general, all-inclusive definition: Life is a self-assembled
(spontaneous, growth), self-organized (order, compartmentation, dif-
ferentiation), self-programmed (information-laden), self-optimized
(steady-state internal milieu, homeostasis), self-sustaining (metabolism,
maintenance, repair, regeneration), semi-enclosed (plasma membrane),
complex molecular system (matter-based), made up of interactive, hier-
archical components and networks (cybernetic, auto-regulation), sup-
ported energetically by thermodynamic disequilibrium (obeys 2nd law
of thermodynamics), carrying out a unified, holistic,^6 self-propelled,