“Oh”, said Goldilocks, “this bowl of porridge is too hot. And this one is too cold. But that one is just right.” And she ate it all up. Then one bed was too hard, the second one was too soft, but the third one was just right. So she curled up in it and went to sleep.
As with Goldilocks and the Three Bears, so it is with our Three Sister Planets. Venus is too hot and has a tremendous greenhouse effect with its CO 2 -rich atmosphere; Mars is too cold with hardly any atmosphere at all; but the Earth is just right. Goldilocks would like it here, as we all do.
It seems that Goldilocks tends to avoid extremes, prefers to sail right down the middle. In this, the little girl is representative of life in general. Life thrives on Earth because of its middle position. But life also prefers middle positions on many other scales. Let us review a few of them.
Life must avoid the extremes of boiling and freezing; i.e. it seeks the middle range of the temperatures at which water is a liquid at atmospheric pressure. (The latter is an Earth-bound concept, but never mind.) The optimum is about 25 degrees C. The range of air and water temperatures suitable for life then has to stay between about -40 and +40 degrees C. This range is rather narrow, and Earth temperature has probably been regulated for billions of years by Gaian mechanisms to stay within this range.
The requirement, implied above, that water must be in the liquid state can be seen as another generalization: life is between the extreme rigidity of a solid and the extreme tenuousness of a gas, mainly in the flexible but stable state of matter characterized as liquid. Solids and gases are utilized by life processes, e.g. skeletal support and breathing by lungs; but most of the process goes on in liquid or semi-liquid phases, aqueous or oily.
Being between water and oil phases is another dimension of life. Oil and water do not mix, of course, so they form two distinct liquid phases. Life not only utilizes both phases, but actively exploits phenomena at the interface of the two. Some parts of proteins are hydrophilic and other parts are lipophilic (or hydrophobic), which helps to determine the structure and function of these building blocks of life. Cell membranes are hydrophilic on both inner and outer surfaces and lipophilic inside, being composed of a bilayer of fatty acids with their polar groups pointing outwards into the aqueous media in both extra-cellular and intra-cellular space. In general, polar groups (with either electric charges or electric dipoles) are hydrophilic (e.g. COOH or NH 2 ), purely covalent groups like long hydrocarbon chains are lipophilic.
Another set is between highly oxidized and highly reduced compounds. With respect to carbon compounds, this means between carbon dioxide and methane. Between CO 2 and CH 4 , life is on the average about CH 2 O, just about halfway. That is the level of glucose, and biochemical processes fluctuate around that state of oxidation. The valence of carbon is +4 in CO 2 and -4 in CH 4 . Although the bonds are covalent rather than electrovalent, the shared electron pair is closer to oxygen than to carbon in a C-O bond and closer to carbon than to hydrogen in a C-H bond. The in-between oxidation states of carbon could then be +3, +2, +1, 0 (as in formaldehyde or glucose), -1, -2, -3, as well as various fractional states. In multi-carbon compounds like ethanol, the overall oxidation number is an average; e.g. in ethanol, one of the two carbons is in a -3 state and the other one is -1, the average being -2. On the whole, we can say that carbon-based life (the only form we know) moves in a broad redox band between CO2 and CH4.
Various other redox systems are also active in life processes; e.g. the central iron atom in hemoglobin is in the Fe+3 state in the oxygenated form and in the Fe+2 state in the reduced form; this enables hemoglobin to function as an oxygen-transporting molecule.
Again, life does best in the middle range between extreme acidity and extreme alkalinity, in a pH range between 6 and 8. Maintaining the pH of the blood at a steady middle-range value is one of the prototypes of homeostasis.
Carbon itself is in the middle (in a left-to-right sense) of the periodic table of the elements. The metals are on the left and the non-metals on the right. Extreme metals (like sodium) tend to combine with extreme non-metals (like chlorine) with an electrovalent bond, as in sodium chloride. Carbon, as an element in the middle, tends to form covalent bonds with non-metals, as well as with itself – hence the ability of carbon to form long chains and rings, and therefore large enough molecules to introduce enough complexity to support life.
Under carbon in the periodic table is silicon, which possibly will get to support a new form of life if computers prove to be capable of artificial intelligence. But this is really based on a different property of silicon, not its ability to bond with itself like carbon. However, this property of silicon is again a “middle” property, namely semiconductivity. As the name indicates, semiconductors like silicon are halfway between electrical conductors (mainly metals) and electrical insulators (mainly non-metals).
While carbon is in the middle of the short period Li (lithium) to F (fluorine) (atomic numbers 3 to 8), the transition metals, (like Fe (iron) which functions in hemoglobin, Cu (copper) in the blood of crustaceans, Mg (magnesium) in chlorophyll, Zn (zinc) in a transcription promoter, and others are in the middle in the longer 18-member periods further down. As indicated by the examples, some of the transition metals function as parts of enzymes and other biological catalysts, particularly because of the variability of their oxidation states, i.e. multiple valence. This is why we need traces of these transition elements as “minerals” in our diets.
Turning now to mental states, life runs between hyper-activity and catatonia, in an equilibrium between mania and depression. An accidental disturbance of this equilibrium may produce an oscillation between the extremes: manic-depressive or “bipolar” disease. It is as if a single attractor split into two attractors, just prior to chaos. A healthy state of mind shows only a mild oscillation (like a thermostat), if any at all. There is a similar equilibrium between chronic anxiety and placidity, between phrenetic political activism and apathy, between frenzy and drowsiness. Many of these polar opposites are linked to levels of particular neurotransmitters in the brain, such as serotonin and adrenalin, high levels usually tending to overactivity and deficiencies to underactivity. With respect to the neurotransmitter dopamine, an excess is linked to schizophrenia (and sometimes to chorea), while a deficiency is linked to Parkinson’s disease. It seems that at one extreme there is too much muscle movement and at the other extreme too little of it.
The above can be further generalized. In chorea there is too little inhibition of spontaneous involuntary movements, while in Parkinsonism there is too much inhibition even of voluntary movement. This stimulation vs. inhibition polarity is the very basis of all neural mechanisms. Connections at synapses between neurons can be either excitatory or inhibitory, and both are necessary for proper balance.
Similarly, our bodies have two kinds of autonomous (involuntary) nervous systems: the sympathetic, which stimulates (e.g. constricts blood vessels, increases the heart rate – like adrenalin in the fight-or-flight reflex); and the parasympathetic, which has the opposite effects. It seems that the two systems keep each other in balance. “Checks and balances” are built in, to prevent overstepping the limits of Goldilocks’ middle band where healthy life resides.
Let us turn briefly now to politics. The polarity between activism and apathy has already been mentioned. The trouble with extreme activism is that it might lead to too much conflict, and possibly violence. This it would do by producing a bi-modal distribution of political views within a nation, which means polarization; this is like a bifurcation in a cusp catastrophe diagram. (See essay on “Swallowtail and Butterfly”.) This situation would be prone to wide swings from one extreme political regime to another at consecutive elections (or revolutions if the system is not democratic), with resultant instability. The opposite of extreme activism, namely extreme apathy, also has dire results: a docile population will passively accept dictatorship and tyranny; democracy would be impossible, the result probably being oppression and deprivation of basic human rights. A healthy political system, one which avoids the extremes of disorder and violence, on the one hand, and injustice on the other, is again Goldilocks’ middle range. There we could hope to realize the values of order, peace and justice simultaneously.
Political opposition movements must also avoid their Scylla and Charybdis; i.e. avoid too much zeal (never trust the government to cooperate with it) while also avoiding cooptation (i.e. trust the government too much). The political parties in Palestine in Jesus’ time were called the Zealots and the Herodians (who cooperated with King Herod, who was subservient to Rome, thus hoping to obtain independence from Rome by this route). They are the prototypes for streams of thought in many contemporary movements. In our time, we fluctuate in our treatment of oppressive regimes: apartheid South Africa, China, Burma, Nigeria, Cuba… ; is it better to engage in punitive economic sanctions or “constructive engagement”?
One more example will suffice: In the Green Party of Germany, there are two factions: the Fundis (adhering to fundamentals and keeping them pure by not cooperating with other parties) and the Realos (“realists” who do cooperate with others in order to obtain political power and achieve at least some of their aims). In peace plans, ecological improvement plans, or indeed any reform plans, this tension is often felt: (1) should we make the plan far-reaching enough to be truly effective if implemented, although such a plan probably will not be acceptable and therefore not implemented; or (2) should we formulate a plan which has a chance of being accepted and implemented, but which would not be completely effective because it does not go far enough. The desirable middle ground is very difficult to find, as any social reformer knows; yet that is where true effectiveness dwells.
Goldilocks developed a feeling for what is “just right” by experimenting and rejecting extremes. It is impossible to define that golden middle ground in the abstract, especially in politics and psychology. (In biochemistry, the experiments were performed by nature aeons ago.) So we end up zig-zagging somewhat, like a thermostat, between the permissible limits. We go through a stormy “crisis” when approaching the frenzy limit, and follow by a quiet plateau when headed for the catatonic limit. (Cf. essay “The Rise and Run” ) Radicals and conservatives should take their turns at the helm. But we must beware of those limits. Those who exceeded them are with us no more.