ecause the animals with variations which gave increased power of flight
would be the ones to escape the lion, while the slower ones would die
without offspring. Thus consciousness would indirectly, though not
directly, result in the lengthening of the legs of the animal and in the
strengthening of his running muscles. Beyond a doubt this factor of
consciousness has been a factor of no little moment in the development
of the higher types of organic machines. We can as yet only dimly
understand its action, but it must hereafter be counted as one of the
influences in the evolution of the living machine.

But, after all, these are only questions of the method of the action of
certain well demonstrated, fundamental factors. Whether by natural
selection, or by the inheritance of acquired characters produced by the
environment, or whether by the effect of isolation of groups of
individuals, the machine building has always been produced in the same
way. A machine, either through the direct influence of the environment,
or as a result of sexual combination of germ plasm, shows a variation
from its parents. This variation proves of value to its possessor, who
lives and transmits it permanently to posterity. Thus step by step, one
part is added to another, until the machine has grown into the
intricately adapted structure which we call the animal or plant. This
has been nature's method of building machines, all based upon the three
properties possessed by the living cell--reproduction, variation, and
heredity.

==Summary of Nature's Power of Building Machines.==--Let us now notice the
position we have reached. Our problem in the present chapter has been to
find out whether nature possesses forces adequate to explain the
building of machines with their parts accurately adapted to each other
so as to act harmoniously for certain ends. Astronomy has shown that she
has forces for the building of worlds; geology, that she has forces for
making mountain and valley; and chemistry, that she has forces for
building chemical compounds. But the organism is neither a world, nor a
mass of matter, nor a chemical compound. It is a machine. Has nature any
forces for machine building? We have found that by the use of the three
factors, reproduction, variation, and heredity, nature is able to
produce a machine of ever greater and greater complexity, with the parts
all adapted to each other. Now the difference between a machine and a
mass of matter