The Outline of Science, Vol. 1 (of 4)

J >> J. Arthur Thomson >> The Outline of Science, Vol. 1 (of 4)

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Interpretation of the Salmon's Story

When an animal frequents two different haunts, in one of which it
breeds, it is very often safe to say that the breeding-place represents
the original home. The flounder is quite comfortable far up the rivers,
but it has to go to the shore-waters to spawn, and there is no doubt
that the flounder is a marine fish which has recently learned to
colonise the fresh waters. Its relatives, like plaice and sole, are
strictly marine. But it is impossible to make a dogma of the rule that
the breeding-place corresponds to the original home. Thus some kinds of
bass, which belong to the marine family of sea-perches, live in the sea
or in estuaries, while two have become permanent residents in fresh
water. Or, again, the members of the herring family are very
distinctively marine, but the shad, which belong to this family, spawn
in rivers and may spend their lives there.

So there are two different ways of interpreting the life-history of the
salmon. Some authorities regard the salmon as a marine fish which is
establishing itself in fresh water. But others read the story the other
way and regard the salmon as a member of a freshwater race, that has
taken to the sea for feeding purposes. In regard to trout, we know that
the ranks of those in rivers and lakes are continually being reinforced
by migrants from the sea, and that some trout go down to the sea while
others remain in the freshwater. We know also in regard to a related
fish, the char, that while the great majority of kinds are now permanent
residents in cold and deep, isolated northern lakes, there are Arctic
forms which live in the sea but enter the rivers to spawn. These facts
favour the view that the salmon was originally a marine fish. But there
are arguments on both sides, and, for our present purpose, the important
fact is that the salmon is conquering _two_ haunts. Its evolution is
going on.

The Romance of the Eel

Early in summer, at dates varying with the distance of the rivers from
the open Atlantic, crowds of young eels or elvers come up-stream.
Sometimes the procession or eel-fare includes thousands of individuals,
each about the length of our first finger, and as thick as a stout
knitting needle. They obey an inborn impulse to swim against the stream,
seeking automatically to have both sides of their body equally
stimulated by the current. So they go straight ahead. The obligation
works only during the day, for when the sun goes down behind the hills
the elvers snuggle under stones or beneath the bank and rest till dawn.
In the course of time they reach the quiet upper reaches of the river or
go up rivulets and drainpipes to the isolated ponds. Their impulse to go
on must be very imperious, for they may wriggle up the wet moss by the
side of a waterfall or even make a short excursion in a damp meadow.

In the quiet-flowing stretches of the river or in the ponds they feed
and grow for years and years. They account for a good many young fishes.
Eventually, after five or six years in the case of the males, six to
eight years in the case of the females, the well-grown fishes, perhaps a
foot and a half to two feet long, are seized by a novel restlessness.
They are beginning to be mature. They put on a silvery jacket and become
large of eye, and they return to the sea. In getting away from the pond
it may be necessary to wriggle through the damp meadow-grass before
reaching the river. They travel by night and rather excitedly. The
Arctic Ocean is too cold for them and the North Sea too shallow. They
must go far out to sea, to where the old margin of the once larger
continent of Europe slopes down to the great abysses, from the Hebrides
southwards. Eels seem to spawn in the deep dark water; but the just
liberated eggs have not yet been found. The young fry rises to near the
surface and becomes a knife-blade-like larva, transparent all but its
eye. It lives for many months in this state, growing to be about three
inches long, rising and sinking in the water, and swimming gently.
These open-sea young eels are known as Leptocephali, a name given to
them before their real nature was proved. They gradually become shorter,
and the shape changes from knife-blade-like to cylindrical. During this
change they fast, and the weight of their delicate body decreases. They
turn into glass-eels, about 2-1/2 inches long, like a knitting-needle in
girth. They begin to move towards the distant shores and rivers, and
they may be a year and a half old before they reach their destination
and go up-stream as elvers. Those that ascend the rivers of the Eastern
Baltic must have journeyed three thousand miles. It is certain that no
eel ever matures or spawns in fresh water. It is practically certain
that all the young eels ascending the rivers of North Europe have come
in from the Atlantic, some of them perhaps from the Azores or further
out still. It is interesting to inquire how the young eels circumvent
the Falls of the Rhine and get into Lake Constance, or how their kindred
on the other side of the Atlantic overcome the obstacle of Niagara; but
it is more important to lay emphasis on the variety of habitats which
this fish is trying--the deep waters, the open sea, the shore, the
river, the pond, and even, it may be, a little taste of solid earth. It
seems highly probable that the common eel is a deep-water marine fish
which has learned to colonise the freshwaters. It has been adventurous
and it has succeeded. The only shadow on the story of achievement is
that there seems to be no return from the spawning. There is little
doubt that death is the nemesis of their reproduction. In any case, no
adult eel ever comes back from the deep sea. We are minded of Goethe's
hard saying: "Death is Nature's expert advice to get plenty of life."

Sec. 4

Forming New Habits

There is a well-known mudfish of Australia, Neoceratodus by name, which
has turned its swim-bladder into a lung and comes to the surface to
spout. It expels vitiated air with considerable force and takes fresh
gulps. At the same time, like an ordinary fish, it has gills which allow
the usual interchange of gases between the blood and the water. Now this
Australian mudfish or double-breather (Dipnoan), which may be a long way
over a yard in length, is a direct and little-changed descendant of an
ancient extinct fish, Ceratodus, which lived in Mesozoic times, as far
back as the Jurassic, which probably means over five millions of years
ago. The Queensland mudfish is an antiquity, and there has not been much
change in its lineage for millions of years. We might take it as an
illustration of the inertia of evolution. And yet, though its structure
has changed but little, the fish probably illustrates evolution in
process, for it is a fish that is learning to breathe dry air. It cannot
leave the water; but it can live comfortably in pools which are foul
with decomposing animal and vegetable matter. In partially dried-up and
foul waterholes, full of dead fishes of various kinds, Neoceratodus has
been found vigorous and lively. Unless we take the view, which is
_possible_, that the swim-bladder of fishes was originally a lung, the
mud-fishes are learning to breathe dry air. They illustrate evolution
agoing.

[Illustration: DIAGRAM OF THE LIFE HISTORY OF THE COMMON EEL (_Anguilla
Vulgalis_)

1. The transparent open-sea knife-blade-like larva called a
Leptocephalus.

2 and 3. The gradual change of shape from knife-blade-like to
cylindrical. The body becomes shorter and loses weight.

4. The young elver, at least a year old, which makes its way from the
open sea to the estuaries and rivers. It is 2/3 inches long and almost
cylindrical.

5. The fully-formed eel.]

[Illustration: _Photo: Gambier Bolton._

CASSOWARY

Its bare head is capped with a helmet. Unlike the plumage of most birds
its feathers are loose and hair-like, whilst its wings are merely
represented by a few black quills. It is flightless and entirely
dependent on its short powerful legs to carry it out of danger.]

[Illustration: _Photo: Gambier Bolton._

THE KIWI, ANOTHER FLIGHTLESS BIRD, OF REMARKABLE APPEARANCE, HABITS, AND
STRUCTURE]

The herring-gull is by nature a fish-eater; but of recent years, in some
parts of Britain, it has been becoming in the summer months more and
more of a vegetarian, scooping out the turnips, devouring potatoes,
settling on the sheaves in the harvest field and gorging itself with
grain. Similar experiments, usually less striking, are known in many
birds; but the most signal illustration is that of the kea or Nestor
parrot of New Zealand, which has taken to lighting on the loins of the
sheep, tearing away the fleece, cutting at the skin, and gouging out
fat. Now the parrot belongs to a vegetarian or frugivorous stock, and
this change of diet in the relatively short time since sheep-ranches
were established in New Zealand is very striking. Here, since we know
the dates, we may speak of evolution going on under our eyes. It must be
remembered that variations in habit may give an animal a new
opportunity to test variations in structure which arise mysteriously
from within, as expressions of germinal changefulness rather than as
imprints from without. For of the transmissibility of the latter there
is little secure evidence.

Experiments in Locomotion

It is very interesting to think of the numerous types of locomotion
which animals have discovered--pulling and punting, sculling and rowing,
and of the changes that are rung on these four main methods. How
striking is the case of the frilled lizard (Chlamydosaurus) of
Australia, which at the present time is, as it were, experimenting in
bipedal progression--always a rather eventful thing to do. It gets up on
its hind-legs and runs totteringly for a few feet, just like a baby
learning to walk.

How beautiful is the adventure which has led our dipper or
water-ouzel--a bird allied to the wrens--to try walking and flying under
water! How admirable is the volplaning of numerous parachutists--"flying
fish," "flying frog," "flying dragon," "flying phalanger," "flying
squirrel," and more besides, which take great leaps through the air. For
are these not the splendid failures that might have succeeded in
starting new modes of flight?

Most daring of all, perhaps, are the aerial journeys undertaken by many
small spiders. On a breezy morning, especially in the autumn, they mount
on gate-posts and palings and herbage, and, standing with their head to
the wind, pay out three or four long threads of silk. When the wind tugs
at these threads, the spinners let go, and are borne, usually back
downwards, on the wings of the wind from one parish to another. It is
said that if the wind falls they can unfurl more sail, or furl if it
rises. In any case, these wingless creatures make aerial journeys. When
tens of thousands of the used threads sink to earth, there is a "shower
of gossamer." On his _Beagle_ voyage Darwin observed that vast numbers
of small gossamer spiders were borne on to the ship when it was sixty
miles distant from the land.

[Illustration: THE AUSTRALIAN FRILLED LIZARD, WHICH IS AT PRESENT TRYING
TO BECOME A BIPED

When it gets up on its hind-legs and runs for a short distance it folds
its big collar round its neck.]

[Illustration: A CARPET OF GOSSAMER

The silken threads used by thousands of gossamer spiders in their
migrations are here seen entangled in the grass, forming what is called
a shower of gossamer. At the edge of the grass the gossamer forms a
curtain, floating out and looking extraordinarily like waves breaking on
a seashore.]

[Illustration: THE WATER-SPIDER

The spider is seen just leaving its diving-bell to ascend to the surface
to capture air.

The spider jerks its body and legs out at the surface and then dives--

--carrying with it what looks like a silvery air-bubble--air entangled
in the hair.

The spider reaches its air-dome. Note how the touch of its legs indents
the inflated balloon.

Running down the side of the nest, the spider

--brushes off the air at the entrance, and the bubble ascends into the
silken balloon.

_Photos: J. J. Ward, F.E.S._]

New Devices

It is impossible, we must admit, to fix dates, except in a few cases,
relatively recent; but there is a smack of modernity in some striking
devices which we can observe in operation to-day. Thus no one will
dispute the statement that spiders are thoroughly terrestrial animals
breathing dry air, but we have the fact of the water-spider conquering
the under-water world. There are a few spiders about the seashore, and a
few that can survive douching with freshwater, but the particular case
of the true water-spider, _Argyroneta natans_, stands by itself because
the creature, as regards the female at least, has _conquered_ the
sub-aquatic environment. A flattish web is woven, somehow, underneath
the water, and pegged down by threads of silk. Along a special vertical
line the mother spider ascends to the surface and descends again, having
entangled air in the hairs of her body. She brushes off this air
underneath her web, which is thereby buoyed up into a sort of dome. She
does this over and over again, never getting wet all the time, until the
domed web has become like a diving-bell, full of dry air. In this
eloquent anticipation of man's rational device, this creature--far from
being endowed with reason--lays her eggs and looks after her young. The
general significance of the facts is that when competition is keen, a
new area of exploitation is a promised land. Thus spiders have spread
over all the earth except the polar areas. But here is a spider with
some spirit of adventure, which has endeavoured, instead of trekking, to
find a new corner near at home. It has tackled a problem surely
difficult for a terrestrial animal, the problem of living in great part
under water, and it has solved it in a manner at once effective and
beautiful.

In Conclusion

We have given but a few representative illustrations of a great theme.
When we consider the changefulness of living creatures, the
transformations of cultivated plants and domesticated animals, the
gradual alterations in the fauna of a country, the search after new
haunts, the forming of new habits, and the discovery of many inventions,
are we not convinced that Evolution is going on? And why should it
stop?

VII

THE DAWN OF MIND

THE DAWN OF MIND

In the story of evolution there is no chapter more interesting than the
emergence of mind in the animal kingdom. But it is a difficult chapter
to read, partly because "mind" cannot be seen or measured, only
_inferred_ from the outward behaviour of the creature, and partly
because it is almost impossible to avoid reading ourselves into the much
simpler animals.

Sec. 1

Two Extremes to be Avoided

The one extreme is that of uncritical generosity which credits every
animal, like Brer Rabbit--who, by the way, was the hare--with human
qualities. The other extreme is that of thinking of the animal as if it
were an automatic machine, in the working of which there is no place or
use for mind. Both these extremes are to be avoided.

When Professor Whitman took the eggs of the Passenger Pigeon (which
became extinct not long ago with startling rapidity) and placed them a
few inches to one side of the nest, the bird looked a little uneasy and
put her beak under her body as if to feel for something that was not
there. But she did not try to retrieve her eggs, close at hand as they
were. In a short time she flew away altogether. This shows that the mind
of the pigeon is in some respects very different from the mind of man.
On the other hand, when a certain clever dog, carrying a basket of eggs,
with the handle in his mouth, came to a stile which had to be
negotiated, he laid the basket on the ground, pushed it gently through a
low gap to the other side, and then took a running leap over. We dare
not talk of this dog as an automatic machine.

A Caution in Regard to Instinct

In studying the behaviour of animals, which is the only way of getting
at their mind, for it is only of our own mind that we have direct
knowledge, it is essential to give prominence to the fact that there has
been throughout the evolution of living creatures a strong tendency to
enregister or engrain capacities of doing things effectively. Thus
certain abilities come to be inborn; they are parts of the inheritance,
which will express themselves whenever the appropriate trigger is
pulled. The newly born child does not require to learn its breathing
movements, as it afterwards requires to learn its walking movements. The
ability to go through the breathing movements is inborn, engrained,
enregistered.

In other words, there are hereditary pre-arrangements of nerve-cells and
muscle-cells which come into activity almost as easily as the beating of
the heart. In a minute or two the newborn pigling creeps close to its
mother and sucks milk. It has not to learn how to do this any more than
we have to learn to cough or sneeze. Thus animals have many useful
ready-made, or almost ready-made, capacities of doing apparently clever
things. In simple cases of these inborn pre-arrangements we speak of
reflex actions; in more complicated cases, of instinctive behaviour. Now
the caution is this, that while these inborn capacities usually work
well in natural conditions, they sometimes work badly when the ordinary
routine is disturbed. We see this when a pigeon continues sitting for
many days on an empty nest, or when it fails to retrieve its eggs only
two inches away. But it would be a mistake to call the pigeon, because
of this, an unutterably stupid bird. We have only to think of the
achievements of homing pigeons to know that this cannot be true. We must
not judge animals in regard to those kinds of behaviour which have been
handed over to instinct, and go badly agee when the normal routine is
disturbed. In ninety-nine cases out of a hundred the enregistered
instinctive capacities work well, and the advantage of their becoming
stereotyped was to leave the animal more free for adventures at a higher
level. Being "a slave of instinct" may give the animal a security that
enables it to discover some new home or new food or new joy. Somewhat in
the same way, a man of methodical habits, which he has himself
established, may gain leisure to make some new departure of racial
profit.

[Illustration: _Photo: O. J. Wilkinson._

JACKDAW BALANCING ON A GATEPOST

The jackdaw is a big-brained, extremely alert, very educable, loquacious
bird.]

[Illustration: _From Ingersoll's "The Wit of the Wild."_

TWO OPOSSUMS FEIGNING DEATH

The Opossums are mainly arboreal marsupials, insectivorous and
carnivorous, confined to the American Continent from the United States
to Patagonia. Many have no pouch and carry their numerous young ones on
their back, the tail of the young twined round that of the mother. The
opossums are agile, clever creatures, and famous for "playing 'possum,"
lying inert just as if they were dead.]

[Illustration: MALE OF THREE-SPINED STICKLEBACK, MAKING A NEST OF
WATER-WEED, GLUED TOGETHER BY VISCID THREADS SECRETED FROM THE KIDNEYS
AT THE BREEDING SEASON]

[Illustration: A FEMALE STICKLEBACK ENTERS THE NEST WHICH THE MALE HAS
MADE, LAYS THE EGGS INSIDE, AND THEN DEPARTS

In many cases two or three females use the same nest, the stickleback
being polygamous. Above the nest the male, who mounts guard, is seen
driving away an intruder.]

When we draw back our finger from something very hot, or shut our eye to
avoid a blow from a rebounding branch, we do not will the action; and
this is more or less the case, probably, when a young mammal sucks its
mother for the first time. Some Mound-birds of Celebes lay their eggs in
warm volcanic ash by the shore of the sea, others in a great mass of
fermenting vegetation; it is inborn in the newly hatched bird to
struggle out as quickly as it can from such a strange nest, else it will
suffocate. If it stops struggling too soon, it perishes, for it seems
that the trigger of the instinct cannot be pulled twice. Similarly, when
the eggs of the turtle, that have been laid in the sand of the shore,
hatch out, the young ones make _instinctively_ for the sea. Some of the
crocodiles bury their eggs two feet or so below the surface among sand
and decaying vegetation--an awkward situation for a birthplace. When the
young crocodile is ready to break out of the egg-shell, just as a chick
does at the end of the three weeks of brooding, it utters
_instinctively_ a piping cry. On hearing this, the watchful mother digs
away the heavy blankets, otherwise the young crocodile would be buried
alive at birth. Now there is no warrant for believing that the young
Mound-birds, young crocodiles, and young turtles have an intelligent
appreciation of what they do when they are hatched. They act
instinctively, "as to the manner born." But this is not to say that
their activity is not backed by endeavour or even suffused with a
certain amount of awareness. Of course, it is necessarily difficult for
man, who is so much a creature of intelligence, to get even an inkling
of the mental side of instinctive behaviour.

In many of the higher reaches of animal instinct, as in courtship or
nest-building, in hunting or preparing the food, it looks as if the
starting of the routine activity also "rang up" the higher centres of
the brain and put the intelligence on the _qui vive_, ready to interpose
when needed. So the twofold caution is this: (1) We must not depreciate
the creature too much if, in unusual circumstances, it acts in an
ineffective way along lines of behaviour which are normally handed over
to instinct; and (2) we must leave open the possibility that even
routine instinctive behaviour may be suffused with awareness and backed
by endeavour.

Sec. 2

A Useful Law

But how are we to know when to credit the animal with intelligence and
when with something less spontaneous? Above all, how are we to know when
the effective action, like opening the mouth the very instant it is
touched by food in the mother's beak, is just a physiological action
like coughing or sneezing, and when there is behind it--a mind at work?
The answer to this question is no doubt that given by Prof. Lloyd
Morgan, who may be called the founder of comparative psychology, that we
must describe the piece of behaviour very carefully, just as it
occurred, without reading anything into it, and that we must not ascribe
it to a higher faculty if it can be satisfactorily accounted for in
terms of a lower one. In following this principle we may be sometimes
niggardly, for the behaviour may have a mental subtlety that we have
missed; but in nine cases out of ten our conclusions are likely to be
sound. It is the critical, scientific way.

Bearing this law in mind, let us take a survey of the emergence of mind
among backboned animals.

Senses of Fishes

Fishes cannot shut their eyes, having no true lids; but the eyes
themselves are very well developed and the vision is acute, especially
for moving objects. Except in gristly fishes, the external opening to
the ear has been lost, so that sound-waves and coarser vibrations must
influence the inner ear, which is well developed, through the
surrounding flesh and bones. It seems that the main use of the ear in
fishes is in connection with balancing, not with hearing. In many cases,
however, the sense of hearing has been demonstrated; thus fishes will
come to the side of a pond to be fed when a bell is rung or when a
whistle is blown by someone not visible from the water. The fact that
many fishes pay no attention at all to loud noises does not prove that
they are deaf, for an animal may hear a sound and yet remain quite
indifferent or irresponsive. This merely means that the sound has no
vital interest for the animal. Some fishes, such as bullhead and
dogfish, have a true sense of smell, detecting by their nostrils very
dilute substances permeating the water from a distance. Others, such as
members of the cod family, perceive their food in part at least by the
sense of taste, which is susceptible to substances near at hand and
present in considerable quantity. This sense of taste may be located on
the fins as well as about the mouth. At this low level the senses of
smell and taste do not seem to be very readily separated. The chief use
of the sensitive line or lateral line seen on each side of a bony fish
is to make the animal aware of slow vibrations and changes of pressure
in the water. The skin responds to pressures, the ear to vibrations of
high frequency; the lateral line is between the two in its function.

Interesting Ways of Fishes

The brain of the ordinary bony fish is at a very low level. Thus the
cerebral hemispheres, destined to become more and more the seat of
intelligence, are poorly developed. In gristly fishes, like skates and
sharks, the brain is much more promising. But although the state of the
brain does not lead one to expect very much from a bony fish like trout
or eel, haddock or herring, illustrations are not wanting of what might
be called pretty pieces of behaviour. Let us select a few cases.

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