The wheel is the archetypal, proverbial, human invention. We don't
just travel on wheels, it is wheels forgive me that make the world go round. Take
apart any machine of more than rudimentary complexity and you'll find wheels. Ship and
aircraft propellers, spinning drills, lathes, potters' wheels our technology runs on
wheels and would seize up without them.
The wheel may have been invented in Mesopotamia during the fourth millennium BC. We know
it was elusive enough to need inventing, because the New World civilisations still lacked
it by the time of the Spanish conquest. The alleged exception there children's toys
seems so bizarre as to prompt suspicion. Could it be one of those false legends, like
Eskimos having 50 words for snow, which spreads purely because it is so memorable?
Whenever humans have a good idea, zoologists have grown accus tomed to finding it
anticipated in the animal kingdom. Why not the wheel?
Bats and dolphins perfected sophisticated echo-ranging systems millions of years before
human engineers gave us sonar and radar. Snakes have infrared heat-detectors for sensing
prey, predating the Sidewinder missile. Two groups of fish, one in the New World and one
in the Old, have independently developed the electric battery, in some cases delivering
currents strong enough to stun a man, in other cases using electric fields to navigate
through turbid water. Squid have jet propulsion, enabling them to break the surface at
45mph and shoot through the air. Mole crickets have the megaphone, digging a double horn
in the ground to amplify their already astonishingly loud song. Beavers have the dam,
flooding a private lake for their own safe conduct over water.
Fungi developed the antibiotic (of course, that's where we get penicillin from). Millions
of years before our agricultural revolution, ants planted, weeded and composted fungus
gardens. Other ants tend and milk their own aphid cattle. Darwinian evolution has
perfected the hypodermic needle (wasp sting), the valved pump (heart), the harpoon (snail
mating dart), the fishing rod (angler fish), the water pistol (archer fish aim water jets
to dislodge in sects from trees above), the automatic focus lens, the light meter, the
thermostat, the hinge, the clock, and the calendar. Why not the wheel?
Now, it is possible that the wheel seems so marvellous to us only by contrast with our
undistinguished legs. Before we had engines driven by fuels (fossilised solar energy), we
were easily outpaced by animals' legs. No wonder Richard III offered his kingdom for
four-footed transport. We also show up poorly against two-legged runners, in the form of
ostriches and kangaroos.
Perhaps most animals would not benefit from wheels because they can run so fast on legs.
After all, until very recently all our wheeled vehicles have been pulled by leg power.
We developed the wheel, not to go faster than a horse, but to enable a horse to transport
us at its own pace or a little less. To a horse, a wheel is something that slows you
down.
Here's another way in which we risk overrating the wheel. It is dependent for maximum
efficiency on a prior invention the road, or other smooth, hard surface. A powerful
engine enables a vehicle to beat a horse or a dog or a cheetah on a hard, flat road or
smooth iron rails. But run the race over wild country or ploughed fields, perhaps with
hedges or ditches in the way, and it is a rout: the horse will leave the car wallowing.
Size for size, a running spider is surely faster than any wheeled vehicle.
Well then, perhaps we should change our question. Why haven't animals developed the road?
There is no great technical difficulty. The road should be child's play compared with the
beaver dam or the bowerbird's ornamented arena. There are even some digger wasps that tamp
soil hard, picking up a stone tool to do so. Presumably these skills could be used by
larger animals to flatten a road.
Now we come to an unexpected problem. Even if road-building is technically feasible, it is
a dangerously altruistic activity. If I as an individual build a good road from A to B,
you may benefit from it just as much as I do. Why should this matter? This raises one of
the most tantalising and surprising aspects of all Darwinism, the aspect that inspired my
first book, The Selfish Gene. Darwinism is a selfish game. Building a road that might help
others will be penalised by natural selection. A rival individual benefits from my road,
but he does not pay the cost of building.
Darwinian selection will favour road-building only if the builder benefits from the road
more than his rivals. Selfish parasites, who use your road and don't bother to build their
own, will be free to concentrate their energy on outbreeding you. Unless special measures
are taken, genetic tendencies towards lazy, selfish exploitation will thrive at the
expense of industrious road-building. The upshot will be that no roads are built. With the
benefit of foresight, we can see that everybody will be worse off. However, natural
selection, unlike us humans with our big, recently evolved brains, has no foresight.
What is so special about humans that we have managed to overcome our antisocial instincts
and build roads that we all share? We have governments, policed taxation, public works to
which we all subscribe whether we like it or not. The man who wrote, "Sir, You are
very kind, but I think I'd prefer not to join your income tax scheme", heard again,
we may be sure, from the Inland Revenue. Unfortunately, no other species have invented the
tax. They have, however, invented the (virtual) fence. An individual can secure his
exclusive benefit from a resource if he actively defends it against rivals.
Many species of animal are territorial, not just birds and mammals, but fish and insects
too. They defend an area against rivals of the same species, often so as to sequester a
private feeding ground, or a private courtship bower or nesting area. An animal with a
large territory might benefit by building a network of good, flat roads across the
territory from which rivals were excluded.
This is not impossible, but such animal roads would be too local for long-distance,
high-speed travelling. Roads of any quality would be limited to the small area that an
individual can defend against genetic rivals. Not an auspicious beginning for the
evolution of the wheel.
Now I must mention that there is one revealing exception to my premise. Some very small
creatures have evolved the wheel in the fullest sense of the word. One of the first
locomotion devices ever evolved may have been the wheel, given that for most of its first
two billion years, life consisted of nothing but bacteria. To this day, not only are most
individual organisms bacteria, but even our personal bacterial cells greatly outnumber our
"own" cells.
Many bacteria are still using thread-like spiral propellers, each driven by its own
continuously rotating propeller shaft. It used to be thought that these
"flagella" were wagged like tails, the appearance of spiral rotation resulting
from a wave of motion passing along the length of the flagellum, as in the wriggling of a
snake. The truth is much more remarkable. The bacterial flagellum is attached to a shaft
that is driven by a tiny molecular engine and rotates freely and indefinitely in a hole
that runs through the cell wall.
The fact that only very small creatures have evolved the wheel suggests what may be the
most plausible reason why larger creatures have not. It is a rather mundane, practical
reason, but it is none the less important. A large creature would need large wheels,
which, unlike man-made wheels, would have to grow in situ rather than being separately
fashioned out of dead materials and then mounted. For a large, living organ, growth in
situ demands blood or its equivalent. The problem of supplying a freely rotating organ
with blood vessels, not to mention nerves, that don't tie themselves in knots is too vivid
to need spelling out.
Human engineers might suggest running concentric ducts to carry blood through the middle
of the axle into the middle of the wheel. But what would the evolutionary intermediates
have looked like? Evolutionary improvement is like climbing a mountain (Mount Improbable).
You can't jump from the bottom of a cliff to the top in a single leap. Sudden precipitous
change is an option for engineers, but in wild nature the summit of Mount Improbable can
be reached only if a gradual ramp upwards from a given starting point can be found.
The wheel may be one of those cases where the engineering solution can be seen in plain
view, yet be unattainable in evolution because it lies the other side of a deep valley,
cutting unbridgeably across the massif of Mount Improbable.
Richard Dawkins is the Charles Simonyi Professor of the Public Understanding of Science
at Oxford University. His most recent book is Climbing Mount Improbable (Viking, £20)