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Remarkably, Humans Are Just the Right Size to Make and Master Fire

Michael Denton
Photo credit: fir0002 flagstaffotos [at] gmail.com.

Editor’s note: We are pleased to present a series adapted from biologist Michael Denton’s book, Fire-Maker: How Humans Were Designed to Harness Fire and Transform Our Planet, from Discovery Institute Press. Find the whole series here. Dr. Denton’s forthcoming book, The Miracle of the Cell, will be published in September.

One need only recall how difficult it is to start a fire using traditional frictional methods (such as rubbing two pieces of wood together), even with the superb manipulative abilities of the human hand, to grasp the uniqueness of our ability among all organisms on Earth to make and master fire. No other organism possesses an organ remotely as capable of initiating a fire. On the possession of the hand alone are we uniquely endowed to be the fire-maker. 

But no matter how wonderfully crafted our hand and upright stance, they would be of no avail unless we were the right size.1 To handle fire, develop metallurgy, make tools for mining ores and hewing wood, and to carry out the innumerable manipulative tasks associated with the development of technology, we need to be approximately the size we are. It is only because our size is fit for the task of fire making that man has successfully followed the long technological journey from the campfires of the ancient African Savannah to the 21st century. And our being the right size to be a fire-maker is itself only possible because a host of basic additional physical and biological parameters are exactly as they are. 

Dimensions and Design

Only an organism of approximately our dimensions and android design — about 1.5 to 2 meters in height with mobile arms about one meter-long ending in manipulative tools — can readily handle fire. An android organism the size of an ant would be far too small because the heat would kill it long before it was even several body-lengths from the flames. Even an organism the size of a small dog one tenth the dimensions of a modern adult human, 20 centimeters tall, possessed of our android design and all our unique anatomical adaptions, would face enormous difficulties in attempting to manipulate fire. Although the recently discovered species of diminutive humans Homo floresiensis2 did use fire, it seems likely that a species any smaller than their reported height of 3.5 feet would have difficulty in maintaining a sufficiently hot fire and building the types of kilns necessary for metallurgy.

In a fascinating article some time ago in the American Scientist entitled “The Size of Man,” the author W. F. Went pointed out that small organisms like “ants or small rodents would have to keep too far away” and “would be unable to bring up enough wood to keep the fire going.”3 In sum, “fire… is only possible with a sufficiently large mass of combustible material which happens to be just correct for use by agents or devices on a scale of human dimensions.”4

Manipulation of the actual fire aside, our size is also critical in carrying out the peripheral activities of building and using fire and for developing metallurgy such as chopping and carrying wood, or mining the materials from which fire can extract the useful metals. As Went commented: “A 3-ft man could neither cut lumber nor excavate a mine in solid rock… Man has adjusted his activities to his particular size; this happened to be sufficient for exploiting fire, hunting larger animals, cutting and splitting wood, and mining minerals.”5 (Emphasis added.)

Stephen Jay Gould alluded to the same point: “Kinetic energy, in some situations, increases as length raised to the fifth power.And he goes on to confess “a special sympathy for the poor dwarfs who suffer under the whip of cruel Alberich in Wagner’s Das Rheingold. At their diminutive size, they haven’t a chance of extracting, with mining picks, the precious minerals that Alberich demands.” Hu Berry made the same point: “Ants cannot use tools like, for example, a hammer because an ant-sized hammer will have too little kinetic energy to drive an ant-sized nail.”7 Organisms significantly smaller than ourselves, even possessed of our android design, lacking the power to hew wood or mine metal ores, would not only be unable to manipulate an actual fire — they would be unable to habitually procure large blocks of wood to fuel the fire and could not mine for metal ores. Neither fire nor metallurgy would be possible. 

Perhaps a Giant, Then?

But would a bipedal primate of our android design but much larger than modern humans be feasible? Probably not. Even as we are, we pay a price for our bipedal posture. For one thing we suffer a number of orthopedic problems. The design of a bipedal primate of, say, twice our height would be severely constrained by gravity and structurally problematic to say the least. Because mass (and weight) increases as L cubed while the strength of bone and the power of muscles increases by L squared, increasing the width of limbs and the size of muscles faces diminishing returns. J. B. S. Haldane made this point with characteristic lucidity in his essay “On Being the Right Size”: 

Consider a giant man sixty feet high — about the height of Giant Pope and Giant Pagan in the illustrated Pilgrim’s Progress of my childhood. These monsters were not only ten times as high as Christian, but ten times as wide and ten times as thick, so that their total weight was a thousand times his, or about eighty to ninety tons. Unfortunately the cross-sections of their bones were only a hundred times those of Christian, so that every square inch of giant bone had to support ten times the weight borne by a square inch of human bone. As the human thigh-bone breaks under about ten times the human weight, Pope and Pagan would have broken their thighs every time they took a step. This was doubtless why they were sitting down in the picture I remember. But it lessens one’s respect for Christian and Jack the Giant Killer.8

Further Problems with Being Too Big

In addition to the gravitational constraint, there are kinetic energy constraints on being too big, as was pointed out again by F. W. Went in the American Scientist

Consideration of kinetic energy shows us another fundamental difference between the macro-world of man and the micro-world of insects and small creatures. The numerical values of kinetic energy actually give us a good clue as to the optimal size of man. A 2 m tall man, when tripping, will have a kinetic energy upon hitting the ground 20-100 times greater than a small child who learns to walk. This explains why it is safe for a child to learn to walk; whereas adults occasionally break a bone when tripping, children never do. If a man were twice as tall as he is now, his kinetic energy in falling would be so great (32 times more than at normal size) that it would not be safe for him to walk upright. Consequently man is the tallest creature which could walk on two legs [an ostrich is the only comparable species but it is about the same height as man]. The larger mammals can become taller, because they are more stable on their four legs.9

Steven Vogel makes the same point: “Tripping is a potential danger to cows, horses, and the like… we run a similar risk even at a lower body mass; the upright posture of humans gives us an unusually great height relative to our [body] mass.”10

There is no escape by envisaging a giant man like Pope or Pagan on a smaller planet where gravity and kinetic forces might present less of a challenge. Worlds significantly smaller than the Earth, where gravitational and kinetic constraints are less, tend to lose their atmospheres and precious oxygen, as discussed earlier in this series.

In short, there are compelling physical reasons why we must be approximately the size we are, to use fire and to possess sufficient strength to mine for ores and hew wood, develop metallurgy, construct metal tools, develop a sophisticated technology, 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,12 can only accomplish an understanding and exploration of our particular world, the universe with the laws of nature as they are, in an android body of approximately the dimensions of a modern human. 

Next, “Just the Right Strength.”

Notes

  1. J.B.S. Haldane, On Being the Right Size and Other Essays (New York: Oxford University Press, 1985).
  2. Michael J. Morwood, Radien P. Soejono, Richard G. Roberts, Thomas Sutikna, Chris S.M. Turney, Kira Westaway, W. Jack Rink, et al., “Archaeology and Age of a New Hominin from Flores in Eastern Indonesia,” Nature 431, no. 7012 (October 28, 2004): 1087–1091. doi:10.1038/nature02956.
  3. Frits Warmolt Went, “The Size of Man,” American Scientist 56, no. 4 (1968): 405.
  4. Ibid., 409.
  5. Went, 408.
  6. Stephen Jay Gould, The Richness of Life: The Essential Stephen Jay Gould. 1st American ed. (New York: W.W. Norton, 2007), 321-322.
  7. Hu Berry, “Ants here, Flies there…Insects, ‘Goggas’ Everywhere!” Flamingo (2006), available at 
  8. NatureFriendsSafari, accessed April 4, 2016. 
  9. Haldane, 1. 
  10. Went, 400-413.
  11. Steven Vogel, Comparative Biomechanics: Life’s Physical World (Princeton: Princeton University Press, 2013), 18.
  12. Aristotle, Metaphysics, I, Chapter 1.