Some time ago, I read Nature's Destiny, a book by Michael Denton, in which he argues that the laws of nature are finely tuned for the support of life as it exists on earth, but not just life in general—human life.
He draws heavily from those things with which man has direct experience. He presents one compelling example after another, and one which is absolutely eloquent in its simplicity and accessibility is Fire and the Dimensions of the Human Body.*
What was Adam's direct experience with the sun, moon and stars? As far as observationally from his point of view, there was a greater light, a lesser light, and tiny pinpoints for the purpose of signs, seasons, days, and years.
In other words, they have meaning and purpose, and it is discernible in their appearance to the unaided eye, as viewed from earth.
*[O]ur ability to handle and manipulate fire is also critically dependent on the basic design and dimensions of the human body being close to what they are. Our ability to handle fire is no trivial ability because it was only through the use of fire that technological advance 'was possible. Through fire came metallurgy and metal tools and eventually chemical knowledge. Because metals are the only natural conductors of electricity, the discovery of electromagnetism and electricity, even the development of computers, are all in the last analysis the result of our ancient conquest of fire.
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That fire is itself a remarkable phenomenon has already been noted. That the chemical reaction between carbon and oxygen is manageable at all is the result of the relative chemical inertness of the carbon atom and dioxygen at ambient temperatures . . . It is only because of the slowness of the combustion of wood that fire can be handled by a large terrestrial organism on a planet like the earth.
Because the smallest sustainable fire is about 50 centimeters across, only an organism of approximately our dimensions and design-about 1.5 to 2 meters in height with mobile arms about 1 meter long ending in manipulative tools-can handle fire. An organism the size of an ant would be far too small because the heat would kill it long before it was as close as several body lengths from the flames. Even an organism the size of a small dog would have considerable difficulties in manipulating a fire. So we must be at least the size we are to use fire, to utilize metal tools, to have a sophisticated technology, to have a knowledge of chemistry and electricity and explore the world. It would appear that man, defined by Aristotle in the first line of his Metaphysics as a creature that "desires understanding," can only accomplish an understanding and exploration of the world, which Aristotle saw as his destiny, in a body of approximately the dimensions of a modern human.
Would an upright bipedal primate much larger than a modern human be feasible? Probably not. The design of a bipedal primate of, say, twice our height and several times our weight would be problematical to say the least. As it is, our upright stance puts severe strain on our lower back, especially on the vertebral discs. Such a gigantic primate would almost certainly require thicker legs, suffer severe spinal problems, and be less nimble than modern man, and certainly no more capable of building a fire. Being the size we are is also essential in another way. It is very unlikely that a brain the size of a bee's, which contains less than a million nerve cells, would be large enough to support intelligence remotely like that of man . . . .
The handling of fire would also be very difficult in an organism without a highly developed sense of vision. And again, only a relatively large organism can possess a high-acuity eye. It turns out, then, that to utilize fire we need to be approximately the size we are for several reasons: to be able to physically manipulate the actual fire itself, to have a brain sufficiently large to support the intelligence required to control that physical manipulation, and to have an eye to see the fire. As well, we need to have manipulative organs somewhat close to the design of arms and hands in modern humans.
Fire and the Size of the Earth
There are some intriguing coincidences related to our biological design and our ability to utilize fire. A carbon-based organism of our size and design possessing an upright bipedal posture is only feasible on a planet of approximately the size and mass of the earth. It is the size of the earth (or more specifically, its total mass) which determines the strength of its gravitational field. This in turn limits the maximum size of large terrestrial organisms like ourselves. If the earth had only twice the diameter, its gravitational field would be eight times stronger and a large upright bipedal creature like ourselves would not be feasible. In a very important sense, then, the earth's size is fit for the design of a bipedal animal of the dimensions of a man and therefore fit for our ability to handle fire.
But this is not all. As we saw in chapter 4, if a planet is to possess a stable hydrosphere and atmosphere fit for life, it must of necessity also possess a mass and consequently a gravitational field very close to that of the earth and undergo the same geophysical evolution. As we saw, its gravity must be strong enough to retain the heavier elements but weak enough to permit the initial loss of the lighter volatile elements, such as hydrogen and helium. Consequently, earth's mass is also fit for the evolution of an atmosphere sim¬ilar to roday's, in density and composition, containing oxygen and therefore capable of sustaining fire.
So the mass of the earth is not only fit for an atmosphere capable of sustaining a complex biosphere and supporting fire, it is also fit for an organism of the weight, size, and dimension capable of utilizing it. The use of fire is of course dependent on additional environmental factors--on the availability of wood, for example, and relatively dry conditions. Unless these additional factors were also favorable, then despite all the physical and mental adaptations which makes us Homosapiens and despite the fitness of the earth as an abode for carbon-based life, neither fire, metallurgy, chemistry, nor any scientific progress would have been possible.
