A SHORT HISTORY OF THE WORLD
BY
H. G. WELLS
4.THE AGE OF FISHES
In the days when the world was supposed to have endured for only a few
thousand years, it was supposed that the different species of plants
and animals were fixed and final; they had all been created exactly as
they are to-day, each species by itself. But as men began to discover
and study the Record of the Rocks this belief gave place to the
suspicion that many species had changed and developed slowly through
the course of ages, and this again expanded into a belief in what is
called Organic Evolution, a belief that all species of life upon earth,
animal and vegetable alike, are descended by slow continuous processes
of change from some very simple ancestral form of life, some almost
structureless living substance, far back in the so-called Azoic seas.
This question of Organic Evolution, like the question of the age of the
earth, has in the past been the subject of much bitter controversy.
There was a time when a belief in organic evolution was for rather
obscure reasons supposed to be incompatible with sound Christian,
Jewish and Moslem doctrine. That time has passed, and the men of the
most orthodox Catholic, Protestant, Jewish and Mohammedan belief are
now free to accept this newer and broader view of a common origin of
all living things. No life seems to have happened suddenly upon earth.
Life grew and grows. Age by age through gulfs of time at which
imagination reels, life has been growing from a mere stirring in the
intertidal slime towards freedom, power and consciousness.
Life consists of individuals. These individuals are definite things,
they are not like the lumps and masses, nor even the limitless and
motionless crystals, of non-living matter, and they have two
characteristics no dead matter possesses. They can assimilate other
matter into themselves and make it part of themselves, and they can
reproduce themselves. They eat and they breed. They can give rise to
other individuals, for the most part like themselves, but always also a
little different from themselves. There is a specific and family
resemblance between an individual and its offspring, and there is an
individual difference between every parent and every offspring it
produces, and this is true in every species and at every stage of life.
Now scientific men are not able to explain to us either why offspring
should resemble nor why they should differ from their parents. But
seeing that offspring do at once resemble and differ, it is a matter
rather of common sense than of scientific knowledge that, if the
conditions under which a species live are changed, the species should
undergo some correlated changes. Because in any generation of the
species there must be a number of individuals whose individual
differences make them better adapted to the new conditions under which
the species has to live, and a number whose individuals whose
individual differences make it rather harder for them to live. And on
the whole the former sort will live longer, bear more offspring, and
reproduce themselves more abundantly than the latter, and so generation
by generation the average of the species will change in the favourable
direction. This process, which is called Natural Selection, is not so
much a scientific theory as a necessary deduction from the facts of
reproduction and individual difference. There may be many forces at
work varying, destroying and preserving species, about which science
may still be unaware or undecided, but the man who can deny the
operation of this process of natural selection upon life since its
beginning must be either ignorant of the elementary facts of life or
incapable of ordinary thought.
Many scientific men have speculated about the first beginning of life
and their speculations are often of great interest, but there is
absolutely no definite knowledge and no convincing guess yet of the way
in which life began. But nearly all authorities are agreed that it
probably began upon mud or sand in warm sunlit shallow brackish water,
and that it spread up the beaches to the intertidal lines and out to
the open waters.
That early world was a world of strong tides and currents. An
incessant destruction of individuals must have been going on through
their being swept up the beaches and dried, or by their being swept out
to sea and sinking down out of reach of air and sun. Early conditions
favoured the development of every tendency to root and hold on, every
tendency to form an outer skin and casing to protect the stranded
individual from immediate desiccation. From the very earliest any
tendency to sensitiveness to taste would turn the individual in the
direction of food, and any sensitiveness to light would assist it to
struggle back out of the darkness of the sea deeps and caverns or to
wriggle back out of the excessive glare of the dangerous shallows.
Probably the first shells and body armour of living things were
protections against drying rather than against active enemies. But
tooth and claw come early into our earthly history.
We have already noted the size of the earlier water scorpions. For
long ages such creatures were the supreme lords of life. Then in a
division of these Palæozoic rocks called the Silurian division, which
many geologists now suppose to be as old as five hundred million years,
there appears a new type of being, equipped with eyes and teeth and
swimming powers of an altogether more powerful kind. These were the
first known backboned animals, the earliest fishes, the first known
Vertebrata.
These fishes increase greatly in the next division of rocks, the rocks
known as the Devonian system. They are so prevalent that this period
of the Record of the Rocks has been called the Age of Fishes. Fishes
of a pattern now gone from the earth, and fishes allied to the sharks
and sturgeons of to-day, rushed through the waters, leapt in the air,
browsed among the seaweeds, pursued and preyed upon one another, and
gave a new liveliness to the waters of the world. None of these were
excessively big by our present standards. Few of them were more than
two or three feet long, but there were exceptional forms which were as
long as twenty feet.
We know nothing from geology of the ancestors of these fishes. They do
not appear to be related to any of the forms that preceded them.
Zoologists have the most interesting views of their ancestry, but these
they derive from the study of the development of the eggs of their
still living relations, and from other sources. Apparently the
ancestors of the vertebrata were soft-bodied and perhaps quite small
swimming creatures who began first to develop hard parts as teeth round
and about their mouths. The teeth of a skate or dogfish cover the roof
and floor of its mouth and pass at the lip into the flattened toothlike
scales that encase most of its body. As the fishes develop these teeth
scales in the geological record, they swim out of the hidden darkness
of the past into the light, the first vertebrated animals visible in
the record.