development. The erect position has given greater freedom to the chest. Man uses fewer organs of locomotion than any other animal. The opossum has two hands, but they are on the hind limbs. The ape has four hands, but must use them all in locomotion. (What is a hand?) The erect position, however, makes spinal deformity easier to acquire, and the whole weight being upon one hip at each step man is liable to hip-joint diseases. In the horizontal trunk the organs lie one behind another; in man they lie one upon another, and are more liable to crowding and displacement. The prone position in sickness helps to restore them. Large blood vessels at neck, armpits, and groins, which occupy protected positions in quadrupeds, are held to the front and exposed to danger. The open end of the vermiform appendix and of the windpipe are upward in the erect trunk of man. Valves are lacking in some vertical veins and present where little needed in horizontal veins. But the freedom of the hands more than makes up for all the disadvantages of erectness.
The Survival of the Fittest.—Those who do not work degenerate. Those who overwork, or work with only a few organs, as the brain and nerves, degenerate. The workers survive and increase in numbers, the idle perish and leave few descendants.
What rate of adjustment to new environment is possible
for man? This has not been ascertained; it is probably much slower than has been generally imagined. The
natives of Tasmania, New Zealand, and many of the
Pacific Islands became extinct in less than a century after
adopting clothing and copying other habits from Europeans.
Life in the country in civilized lands differs less
from the environment of primitive man than does life in
cities. Cities have been likened to the lion's cave in the
fable, to which many tracks led, but from which none led.
The care of health in cities is now making rapid strides
along the biological basis of purer air, more open space, less
noise, simple food, and pure water. Biology, by supplying
as a standard the conditions which molded man's body
for ages, furnishes a simple and sure basis for hygiene.
To mention one instance among many, man blundered for
centuries in attempting the cure of consumption, and well-
