Man In The Modern World

THE SIZE OF LIVING THINGS
THE size of things has a fascination of its own. There is a certain
thrill in hearing that a fish weighing hundreds of pounds has
been caught with rod and line; that one of the big trees of California
has an archway cut through its bole capable of letting a stagecoach
pass; that the bulkiest of men have attained a quarter of a ton
weight; that it takes two harvest mice to weigh as much as a half-
penny ; that an average man contains only about two and a half cubic
feet; or that many bacteria, capable of producing virulent diseases,
are so small that it would take over three hundred, end to end, to get
from one side to the other of the full stop at the end of this sentence.
But when we look into the subject more systematically, the passing
thrill of surprise gives place to a deeper interest. For one thing, we
shall find ourselves confronted by the problem of the limitations of
size* Why has no animal ever achieved a weight of much more than
a hundred tons? Why are the predatory dragon-flies never as large
as eagles, or these social beings, the ants, as big as those other social
beings, men? Why do lobsters and crabs manage to reach weights
more than a hundred times greater than the biggest insect, but more
than a thousand times smaller than the biggest vertebrates? Why, to
choose something which at first sight seems to have nothing to do with
size—why do you never see an insect drinking from a pool of water?
As we follow up the clues, we shall begin to understand some of life's
difficulties in a new way—the difficulties attendant upon very small
size, the quite different difficulties attendant upon great bulk; and
we shall realize that size, which we are so apt to take for granted,
is one of the most serious problems with which evolving life has had
to cope.
Reflection upon our own size will also help us toward an estimate
of our position in the universe—of how we stand between the infinitely
big and the infinitely little. It has been only in the last few decades
that this estimate could be justly made. We knew the bulk of the big
trees and whales; but not till quite recently did the existence of filter-
passing viruses reveal to us the lower limit of size in life. And when
we pass to the lifeless background, we seem, in discovering the elec-
tron, to have attained to the ultimate degree of smallness, to the
indivisible unit of world stuff; and the development of Einstein's
theory has made it possible to state at least a minimum weight for the
entire universe. Where does the physical body of man stand? Is he
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