The transformation from non-living to living requires two steps. First, environmental sources must provide the energy needed to add an atom or two (also taken from the environment) to a molecular complex. This changes the molecule, as it now has one or more additional atoms and a little bit more energy (the amount needed to attach the extra atoms). In the second step, this process is reversed; the added atoms and energy have to be returned to the environment—otherwise nothing more than a chemical activity is occurring (or the entity is growing, see below). Movements within the fluid environment surrounding the molecule would bring new nutrients, and the process would repeat. (Fluid environments, liquid or gas, are vital to life’s beginnings because life needs a continuous supply of energy and raw materials to survive. A point of interest: the complex would be slowly propelled and could stumble upon its own supplies, if its configuration ejected surplus atoms repeatedly in one direction.)
(Where supplies exist to form one kind of molecular complex [see Possible Origins Of Life On Earth concerning life’s beginning], other kinds of biotic complexes might also arise. Once this happens, the most efficient process would sweep up available resources. Environmental variations would favour the formation of different complexes, however. Thus, right at life’s beginning, natural selection seems inevitable.)
Occasionally, different atoms may have become permanently attached to the original molecular complex. Adding extra atoms to any molecule changes its properties; most changes would presumably prevent the complex from continuing its energy processing, and it would “die.” However, some additions would not cause “death” and would thereby enlarge the complex, which might eventually grow big enough to split apart or replicate. However, it is not growing, nor even reproducing, that hallmarks life; it is the particular kind of energy transformations that extract from “without” to utilize “within,” while the totality within retains its overall identity. Homeostasis first arose at life’s beginning, and remains a fundamental property of life, equal in stature to life’s ability to process energy.
Only one such molecule needed to form for life to begin. However, it is likely that conditions permitting the formation of the first self-sustaining molecular complex occurred in many places. If so, then many such molecules, identical or differing slightly one from another, could have formed more or less simultaneously.
The first bounded, self-sustaining, molecular complexes might not have been able to grow and split. Many might have formed only to be broken apart by external forces after existing for a period of time. Nevertheless, this situation would provide opportunities for molecular alterations to occur, and thus a variety of molecular structures to have arisen. Eons probably passed before such complexes became capable of self-replication.
Replication requires a means whereby each internal physical/chemical process is duplicated in the replicated entity. A bacterium reproduces by binary fission, whereby its single chromosome replicates and the bacterium splits into two. Some one-celled animals and plants also simply duplicate each internal component then split apart (amoebae, for example, replicate this way). At some time, one or more of the prototype living molecular complexes must have developed the ability to replicate (and probably did so by growing, then fissioning).
We can now expand upon the point made in The Behaviour Of Living Things in this chapter: life assertively reaches for and grabs hold of new territory because it needs the energy this territory contains to continue living. Life began as an energy-exploiting process and continued in that manner. It later developed the ability to replicate and hence to evolve in the sense we use that word. Subsequent beneficial mutations conferred an increasing ability to exploit different environmental energy niches, leading, slowly but inexorably, to the complexities of the many different life forms we see all around us today.
The phenomenon of life turns out to be just the behaviour of a bunch of complex molecules, co-operating within one body in order to exploit the many various environments inside and outside that body, to obtain the energy they need to sustain and replicate themselves. The whole body is said to be “living,” but it is so only because each one of its constituent processing molecular complexes is living. In essence, biology is chemistry-in-action, and chemistry is physics-in-action. Feynman knew, decades ago, that life’s basis had to be this simple.
- Attaching atoms to, or releasing atoms from, a molecular complex invariably results in the loss of some energy to the environment; thus the complex cannot simply reuse the same energy it has just released. (It would be a perpetual-motion machine were this not so.)
- It is likely that this process is ongoing, continually occurring on Earth even today at sub-life levels in fluid environments of sufficient complexity. However, energy-enriched molecules, of any kind, living or dead, make excellent fodder for omnipresent bacteria and therefore would not survive very long.
- Freeman Dyson, in Origins of Life (Cambridge: Cambridge University Press, 1999) hypothesized that life began twice; once as a metabolic (or energy-processing) entity, and once as a replicating entity, with the two forms later uniting.
I cannot understand how an entity could replicate without an energy-processing mechanism being involved. (A virus is a replicating entity, but (in many people’s opinion) it is not a living one. It has to control its host’s energy-exploiting mechanisms before it might be said to be living.)
- See page 20 of Richard P. Feynman’s book, Six Easy Pieces (Reading Massachusetts: Addison-Wesley Publishing Company, 1995). Although based upon a series of lectures first presented in 1963, their originality still makes this book very enjoyable reading.