28. Discovering the forces behind natural selection

Mayer’s important discovery of the difference between mechanical and nonmechanical chemical work is precisely the insight we have been looking for. It allows biological entities to create and exploit gradients and potentials … and it will even eventually allow us to separate the intrinsic from the extrinsic and measure a precise value for natural selection.

We cannot get to our destination without first appreciating that Newton’s system was established by, above all else, its ability to equate the kinetic and the potential energies. Therefore, without some similar concept of a potential within biology, there is little hope for similarly unifying and clarifying the biological sciences.

Figure 28: Biological Potentiation
 Biological Potentiation

The weight in Figure 28, attached to a spring, is filled with potentialities and actualities. It can oscillate up and down, and its properties are relatively easy to measure. A scientist can drop a weight from several different heights and observe that there is a straightforward relationship between the gravitational potential energy, UG, and height, h. The relationship UG = mgh is rapidly derived where m is mass and g is an expression for the strength of the gravitational field. The formula tells us the weight’s potential energy at every point on its oscillatory path.

The formula for potential energy seems easy enough, but it should not blind us to the realization that it depends on a prior knowledge based upon experience. We keep on dropping weights from different heights to spot the pattern … and we then keep on dropping weights to confirm that pattern. The given formula simply obviates the memorization of a vast database of values of potentialities versus actualities.

The spring’s kinetic energy, due to its motion, is the resultant of its above gravitational potential. It is an actualization of a potential, and simultaneously the potentiation of a future actuality. That kinetic energy’s expression at each point on its path, which is EK = mv2/2, can be derived in a fashion similar to the above. It is therefore not far behind. But this “book of nature” that tells us about these kinetic and potential energies still depends on prior knowledge and a succession of trials. It is also relatively easy to read. We can calculate values for potential and kinetic energies very simply. Because of those formulae, we do not need a “book of tables” for either property.

Although biology also has its transitions, potentialities, and actualities, biological phenomena do not seem nearly so predictable as the potential and kinetic energies. Inevitably, efforts are made, such as by Jørgensen and Fath (2004), to explain these thermodynamically:

The thermodynamic principles of ecology are proposed to explain growth and development observed in ecological systems. In general, growth means an increase in system size, while development is an increase in organisation independently of system size. … Everywhere in the universe there are structures and gradients resulting from growth and development processes cutting across all levels of organization. A gradient is understood as a difference in an intensive thermodynamic variable, such as temperature, pressure, altitude, or chemical potential. Growth is defined as an increase in a measurable quantity, often taken in ecology to be biomass …. (Jørgensen and Fath, 2004, p. 270).

Laudable as such attempts are, they do not result in what biology needs, which are potentials. When, for example, a doe or female deer is pregnant, she is literally pregnant with potentialities. Through being a pregnant female, she is filled with a set of potentialities that a buck or male deer is not, and never will be. But a young buck, approaching his first adult season is also “pregnant” with potentialities … and he is filled with them in a way that a doe simply is not, and never will be. What is of particular relevance to biology and ecology is that the buck actualizes his potentialities by going into rut. And again of relevance to biology is that when the doe’s fawn is eventually born, she not only ceases to be pregnant, she actualizes the potential to give birth that she once presented. And when the buck first impregnated the doe he, also, actualized potentialities that he previously possessed. All these potentials ceased as the actualities began.

Biological populations cannot be properly analysed without a rigorous and systematic method for measuring the events and issues involved in the succession of biological potentialities and actualities that mark out a biological cycle. As Brown et al state, they involve both mass and energy:

Energy is required to perform biological work, including acquiring and transforming material resources. Materials, both carbon compounds and elemental nutrients, are required to synthesize the chemical compounds that are the basis of all biological structures and functions. At all levels, from individual organisms to ecosystems, the processing of energy and materials is linked due to metabolic constraints (Brown et al, 2004).

Although biological phenomena do not seem nearly so predictable as potential and kinetic energy, they are not without their regularities. When, for example, we see a doe and/or a buck whose masses are about 20 and 30 kilogrammes respectively, we automatically consult a rough-and-ready ecological “book of deer.” This is our ecological knowledge, garnered from experience, of the biological trajectory pertinent to such animals, each of which is a set of molecular and chemical components. From that experience, we can guage their approximate ages and states of health. This is in fact a potentiality because we can also predict that if they each survive for long enough, then they will each approximately double their weights to the general adult size of 40 and 60 kilogrammes for the doe and the buck respectively.

This ecological “book of deer” we consult will probably never be reduced to a mathematical formula, but year after year, does and bucks repeat the same kinds of interactions, of potentialities, and of actualities. These also have a certain air of regularity and predictability. The “book of Brassica rapa”, the “book of deer”, the “book of gravitational potential” and the “book of kinetic energy” are all written by experiment and/or experience, and the precise formulae used in the seemingly easy potential and kinetic energy cases does not belie the similarity of their origins.

Thermodynamicists worked hard at formulating their subject consequent to the discoveries made by Mayer, Joule and others. They of course wanted to emulate the spectacularly successful model provided by Galileo, Newton, and others. But unfortunately, developing the same kind of language was considerably more challenging. It was eventually achieved by the German physicist Hermann von Helmholtz, and also by the US physical chemist Josiah Gibbs. The “book” of the Helmholtz and the Gibbs energies they provided is not as intuitively easy to “read” as are a spring and gravity, but it is no less predictable. The relevant potentialities show themselves in the actualities of the pressures and the volumes of thermodynamic systems.

In 1854 Helmholtz, working independently, came to the same realization as Mayer about the conservation of energy, and published his own treatise on the subject. When a system has expanded, then its Helmholtz energy, which is its ability to do work, has declined because its pressure has decreased while its volume has increased. That work is the actualization of its previous potential as measured by the Helmholtz energy named in his honour. Helmholtz gave the now accepted explanation for the interaction between pressure and volume, P and V. He gave clear definitions of internal energy, U, available work, A, and other such concepts. The Helmholtz energy is that part of any system’s stock of energy that is capable of doing mechanical work, and in the manner of equivalency regarding mechanical work and the constant pressure piston described above, and as Mayer had noted before him (Callen, 1985; Encyclopaedia Britannica, 2002; Atkins, 1990; Fowler, 2008).

Although Black’s earlier work on latent energies and phase transitions was seminal, theoretical gaps remained. Gibbs later addressed himself to what had by then become one of the major outstanding problems in physics and chemistry: accounting for these phase changes and transitions first highlighted by Black. Black had already given a method for determining phase change enthalpies. The ‘Gibbs energy’—which is how it is formalized—is a measure of chemical potential and reactivity (Atkins, 1990).

Thanks to Gibbs, it is now straight forward to procure, for example, three flasks of given size and fill them with gases, one of oxygen, O2, and two of water, 2H2. We can now combine them under appropriate conditions, and ignite a spark. A considerable amount of measurable energy is given off in an exothermic reaction; and an equally measurable amount of water is given off in the well-known chemical reaction 2H2 + O2 = 2H2O. That energy can, in principle, be used to do work through its changes in pressure and volume. These interact in predictable ways with temperature, the total heat energy, and the chemical configurations all evolved in the reaction. We can now write those mass and energy values in a book or set of tables. Then the next time anyone else tries this, they can first consult our tables. When they “read” the book we give them—which is also a “book of nature”, albeit a less convenient one—they can predict the result for those same potentialities and conditions. The Gibbs energy is a measure of the potential reaction enthalpy—i.e. the pent-up chemical energy—contained in the bonds of the molecules in the flasks when they are in their initial state. That Gibbs energy can now be assigned to those molecules, and it accurately predicts their behaviour, their work, and their heat energy as evidenced in their Helmholtz energies, which is a sum of all energies. The Gibbs and the Helmholtz energies may again not be as intuitively obvious, but they are nevertheless real, measurable, and predictable. They also allow us to express biological potentials.

If a buck and a doe are each going to double in mass, then they must—in Mayer’s terms—engage in a given quantity of mechanical chemical work. All the molecules concerned must be pulled into each of the buck and doe, and they must be pulled in against the force to retain them constantly exerted by the environment. This activity to increase the net number of molecules in each is thus a constant pressure, CP, situation. Since it is mechanical chemical energy, it involves pressure and volume and we can measure it—molecule by molecule—through the Helmholtz energy.

The developmental changes the buck and doe must then undergo, consequent to the above acquisition of molecules, are changes in chemical configuration and in chemical bond energy. They do not incur the expenses of acquisition. The number of molecules in the buck and the doe remains invariant. This is a nonmechanical form of chemical energy. These development changes therefore occur in a constant volume, CV, situation. And since it is a nonmechanical form of energy, we can measure it—again molecule by molecule—through its Gibbs energy. And these two—the Helmholtz and the Gibbs energies—are the potentials and the forces that drive all biological creatures … and that therefore drive their natural selection.