This tale will be told in a meandering manner, inter-posing various side issues as they occur to me, in “stream of consciousness” style. Nevertheless, there will be a continuous thread that can be picked up from beginning to end.

Penrose says, in “Shadows of the Mind”, that voluntary movements and thoughts (“free will”) operate through quantum mechanisms; essentially through brain structures being able to sustain superposed states for a time rather than imme-diately flipping to one or the other. In terms of neurons, this means simultaneously firing and not-firing. This vio-lates a fundamental principle of logic, namely that a pro-position and its negation cannot be simultaneously both true; but such is the nature of quantum theory “weirdness”, as well as of “fuzzy logic”.

Penrose calculated that “the metabolic energy flux” (presumably in humans) would be sufficient to do this. (Why does it take energy? I don’t really know.)

Metabolic energy flux is different in different orga-nisms. I want to argue that, besides continuous gradations, there are also two sharp breaks (increases): one is from anaerobic to aerobic respiration, and the other is from exothermy (cold-blooded animals) to endo-thermy (warm-blooded animals).

Anaerobic metabolism occurs only in bacteria, i.e. pro-karyotes. (But all bacteria are not prokaryotes, some are aerobic, or the facultative in-betweens.) Archeobacteria and other early forms may metabolize methane or sulfur compounds (e.g. those at hydrothermal vents at spreading ridges on the ocean floor), but many use glycolysis: the breakdown of glu-cose to lactic or pyruvic acid, i.e. from 6-carbon to 3-carbon compounds. (This is sometimes called fermentation, and even a fungus like yeast – a eukaryote – may do it.) Glycolysis produces a relatively low energy flux, and so possibly bacteria and yeasts cannot maintain quantum super-position and cannot really “think”.

There was a tenfold (approximately) increase in the rate of energy production in the step-up to aerobic re-spiration, when the lactic or pyruvic acid (products of glycolysis) were further processed via the Krebs cycle right through to carbon dioxide and water. This could not happen until there was enough oxygen in the atmosphere. This oxygen came from photosynthesis; so until photosynthesis was inven-ted by some other prokaryotes (the cyanobacteria), aerobic respiuration, with its higher energy production rate, could not begin.

The Krebs cycle takes the 3-carbon compounds right to the 1-carbon stage (CO2). The hydrogen from its various stages is passed along by a “bucket brigade” of redox enzymes until it finally recombines with oxygen to form water. Hydrogen-oxygen recombination is a highly exothermic (energy producing) reaction, explosive under some condi-tions. However, in living cells it is done – oh, so gradually and delicately, so that it no longer resembles “burning”, although the final result is the same.

The redox cascade of enzymes reminds me of the series of downward locks on the Rideau Canal at both ends, in Ottawa beside the Chateau Laurier into the Ottawa river and at Kingston Mills into Lake Ontario; or the bigger ones on the Welland Canal from Lake Erie to Lake Ontario. The series of locks substitutes for a waterfall, like the one on the Rideau River in Ottawa beside the City Hall, or even more spectacularly, Niagara Falls. Similarly, the redox enzyme cascade of aerobic respiration substitutes for rapid burn-ing, or more spectacularly, for a powerful explosion.

The 3C Krebs cycle is also an ingenious way to slow down the sloughing off of carbon dioxide and hydrogen in gradual stages rather than all at once. It is mediated (as is the redox cascade) by the ATP-ADP reaction (or similar ones with nucleotides other than adenosine – the “A” of ATP) which then stores the energy in its high-energy phosphate bonds for future use in muscle action – or “thinking”.

Although these metabolic slowdowns, so necessary to prevent the organism from “burning up”, decrease the rate of energy production (the flux or power), there might be almost enough to sustain Penrose’s quantum superposition mainte-nance.

It is amazing that these nucleotides (like adenosine and others, the purines and pyrimidines), are the same ones that constitute the “rungs” in the DNA and RNA “ladders”. Freeman Dyson in “Infinite in All Directions” points out the connection: DNA and RNA may have originated at the dawn of life from an “accidental” polymerization of these energy-storing units. The nucleotides, instead of storing energy, came to store information. A different function; or is it really so different, if energy and information are deeply connected? (See my essay The Three Essences.)

After this long digression, back to the original story. Aerobic respiration, with its tenfold speed in energy production, could not have come about until the arrival of photosynthesis, which provided the oxygen. But would this higher energy flux be sufficient for thought, free will, and consciousness? Perhaps, perhaps not. Penrose does not say, and I don’t know how he did the calculation for humans. There might be enough energy in these aerobic systems for some occasional, but not sustained, quantum superposition or tunnelling (an alternative quantum mechanism).

Even human consciousness, according to Dennett, is punctilistic, not continuous: like viewing a series of “stills” on a movie film and perceiving them as motion. (Could this somehow be the origin of our sense of time as an irreversible and unspeedable flow beyond our control?)

But let us proceed to the second upgrade in the rate of energy production, which occurred in the transition from exothermic animals (those whose temperature is the same as that of the environment and fluctuates with it, in daily night-and day terms and seasonal cycles) to endothermic animals (who maintain a constant body temperature consi-derably above that of the environment). This transition happened independently in birds and in mammals. (It is unknown in phyla other than vertebrates.) Birds and mammals can generally move faster than fishes, amphibians, and reptiles (though the status of dinosaurs is in dispute), and they are not so dependent on the weather or the ambient temperature in general, so that some (like owls) can be nocturnal. (Fishes can move relatively fast because of their rigid body shape and the properties of water as a medium; and snakes can slither and frogs can hop, because of func-tional peculiarities.) (Insects can move fast in spite of being exothermic, because of their small size and weight.)

Can birds and mammals also “think” better? They do take better care of their young, which takes some thinking. The mammalian brain is generally thought to be an upgrade from the reptilian brain. (In humans the cortex is an additional layer.)

Now let us look at the other four kingdoms of life besides animals, especially the plants. Plants have aerobic respiration, but of course no endothermy. They practice photosynthesis along with aerobic respiration, which in the overall result (but not in the detailed mechanism) is the opposite process; but in the presence of sunlight (by day), photosynthesis is faster than respiration.

Photosynthesis, while deriving most of the energy from sunlight, also requires some expenditure of metabolic energy for its “dark phase” of sugar synthesis. This would subtract somewhat from the aerobic metabolic energy flux, as would the plants’ other chemical syntheses of a prodigious variety of terpenes, alkaloids, and aromatics, many of them useful in human medicine, but some dangerous as poisons or habit-forming drugs. One might say that, while animals excel in locomotion, plants (and some fungi) specialize in chemical synthesis instead.

Plants sometimes have slow locomotion, like turning leaves toward the sun as it moves across the sky, or flowers closing up at night and opening at dawn. However, they usually don’t have fast locomotion (except for carnivorous plants like the Venus flytrap), because they are attached to the soil by their roots. Some early marine animals, some still surviving today, are also sedentary or sessile: e.g. corals and sea anemones. Non-experts sometimes wonder why they are not classed as plants rather than animals. (The terms “anemone” and “sea Cucumber” reflect such doubts.) Similar, why are carnivorous plants like the Venus flytrap not classed as animals?

These doubts in the popular mind show how deeply ingrained are our ideas about plants being sedentary and animals having fast locomotion. But biologists use different traits in their classifications.

In any case, plants have no muscles and no nervous systems. While the actin and myosin that compose muscles in animals exist within all cells (internal organelles such as microtubules and microfilaments are present in the cells of all five kingdoms of life, sometimes making cilia and flagella move in locomotion of bacteria and protists), in plants they do not form the macroscopic structures we know as muscles.

Excitability (irritability) exists in all kingdoms of life as well, but neurons as specific excitable structures exist only in animals.

Back to our main story. Warm-blooded animals (mammals and birds) presumably have enough metabolic power (defined as the rate of energy production per unit time) to use quantum superposition for a voluntary steering of events, usually called free will.

Free will is an important part of consciousness, but not all of it; there is also introspection and a sense of self and a sense of others as similar to oneself. Self-awareness apparently originated in the primates with some apes, like the chimpanzee and the orangutan (see article in Discover, November 1996, by Sarah Richardson, citing work by Daniel Povinelli), but awareness of others as oneself is peculiar to Homo sapiens, and can be seen as the basis of human ethical systems based on compassion. Language is probably important in our sense of others, as we experience communication of the “I – Thou” type, in the terminology of Martin Buber.

We are beginning to understand the physical basis of “degrees of consciousness” in different life forms. Although there are some sharp upgrades and changes in slope, there is a continuous line without breaks in the evolution of mind from matter. “Emergence” is a more apt concept at some points, but there is a smooth ascent nevertheless.