selection is continuous and never-ending, except in rare and special
circumstances, such as man may bring about by his interference,
and then it does not really cease but only changes its demand. The
characteristics of a race or species are maintained by natural
selection, just as much as they are produced by it. Cessation of a
previously active selection (which is sometimes brought about by
exceptional conditions) results in a departure of the individuals of
the race, no longer subject to that selection, from the standard of
form and characteristics previously maintained. To understand this, we
must consider for a moment the great property of living things, which
is called “variation.”
No two animals, or plants even, when born of the same parents, are
ever exactly alike. Not only that, but if we look at a great number of
individuals of a race or stock, we find that some are very different
from the others, in colour, in proportion of parts, in character, and
other qualities. As a rule it is difficult to look at such a number,
because in Nature only two on the average out of many hundreds,
sometimes thousands, born from a single pair of parents, grow up to
take their parents’ place, and these two are those “selected” by
natural survival on account of their close resemblance to the parents.
But if we experimentally rear all the offspring of a plant or animal to
full growth--not allowing them to perish by competition for food, or
place, or by inability to escape enemies--then we see more clearly how
great is the in-born variation, how many and wide are the departures
from the favoured standard form which are naturally born and owe their
peculiarities to this birth-quality--called innate or congenital
variation--and not to anything which happens to them afterwards
differing from what happens to their brothers and sisters.
Of course, we are all familiar with this “congenital or innate
variation,” as shown by brothers and sisters in human families. How and
why do innate variations arise? They arise from chemical and mechanical
action upon the “germs” or reproductive cells contained in the body of
the parents, and also sometimes from the mating in reproduction of two
strains or races which are already different from one another. When
an animal or plant is given unaccustomed food or brought up in new
surroundings (as, for instance, in captivity) its germs are affected,
and they produce variations in the next generation more abundantly. The
best analogy for what occurs is that of a “shaking up” or disturbance
of the particles of the germ or reproductive material, somewhat as
the beads and bits of glass in a kaleidoscope are shaken and change
from one well-balanced arrangement to another. And the same analogy
applies to the crossing or fertilising of “strain” or “race” by another
differing from it. A disturbance is the consequence, and a departure
in the form and character of the young from anything arrived at
before often takes place. These variations have no necessary fitness
or correspondence to the changed conditions which have produced them.
They are, so to speak, departures in all and every direction--not
very great, but still great enough to be selected by survival if
occurring in wild extra-human nature, and obvious enough when produced
in cultivated animals and plants to be seen and selected by man, the
stock-breeder or fancier.
Indeed the stock-breeder and horticulturist go to work in this way
deliberately. Though when they have fattened an animal or fed up a
plant they cannot make it transmit its fatness or increased size
to its offspring, yet they can, by special feeding and change of
conditions of life--or by cross-breeding--break up the fixed tendency
or quality of the germs within the parents so treated. Thus they get
offspring produced which show strange and unexpected variations of
many kinds--new feathers, new colours, new shapes of leaf, increased
size of root, length of limb--all kinds of variations. From the
congenital varieties thus produced by “stirring up,” “breaking down,”
or disturbing the germ-matter (germ-plasm) of the parents, the breeder
next proceeds to select and mate those which show the character which
suits his fancy, whilst he destroys or rejects the others. Thus he
establishes, and by repeated selection in every generation maintains,
and if he desires increases, the characteristics which he values.
Birth-variation is then an inherent property of living things
(including man) as much as heredity, which is the name for the
property expressed in the resemblance of offspring to parent. And
birth-variation, or congenital variation--that is to say, the being
born with a power to grow into something different (not greatly, but
still obviously, different) from their parents or ancestry, and from
their brethren and cousins, though not subjected after birth to any
treatment or conditions differing from those common to all of them--is
a quality of living things which must be distinguished altogether from
the power of the individual itself, though not born with qualities
differing from those of its brothers and sisters, to vary or change in
some respects as compared with other individuals when it is specially
fed or exposed to special treatment. The first is change, or variation,
of the “stirps,” or germ plasm; the second is change, or variation, of
the transient body of the individual. The first is indefinite and may
be of almost any kind or form; once it has appeared, it is a permanent
possession of the race descended from its owner. The second is definite
and a direct reaction to the environment. Such an individually induced
or stimulated change is often called an “acquired character.” It does
not affect the stirps, the inner reproductive germs, and cannot be
handed on by inheritance to a new generation.
What happens, then, when there is a cessation of selection? All
sorts of birth-variations appear and grow up. The fine adjustment of
form--maintained by natural selection carried on unceasingly--no longer
obtains. The characteristics of the race become less emphasised. All
sorts of birth-variations have an equal chance, and the tendency must
be for those characteristics which have most recently been established
and maintained by severe selection to dwindle and then to disappear
altogether. The majority of birth-variations will--when selection is
prevented--always tend to present a lessened, rather than an increased,
development of any one characteristic--the excelling minority will
no longer be selected, but all will have an equal chance in mating
and reproducing. Hence, bit by bit, all salient features, all the
characteristics of the race previously maintained by selection, will,
as a result of survival of all variations and general crossing and
interbreeding--dwindle and disappear. It is to this process that the
term “degeneration” has been applied by biologists. How far it may go,
and what are its limits and various outcomes, I cannot now discuss.
It is sometimes spoken of as “retrogression”--which implies wrongly a
return to a previous state. From some points of view it might be called
“simplification.”
The point to which I have been making is this--that civilised mankind
appears to be very nearly in regard to most points of structure
and quality in a condition of “cessation of selection.” It is the
better-provided and well-fed, well-clothed, protected classes of the
community, in which this cessation of selection is most complete.
Racial degeneration is, therefore, to be looked for in those classes
quite as much as in the half-starved, ill-clad, struggling poor,
if, indeed, it should not be expected to be more strongly marked in
them. There are facts which tend to show that such anticipations are
well-founded.
This is a matter requiring further discussion. It is probable, I may
say in anticipation, that whilst natural selection in the struggle for
existence is only obscurely operative (except as to alcoholism and
some diseases) in civilised man, yet what Mr. Darwin called sexual
selection--the influence of preference in mating--has an important
scope, and it may be that hereafter it will be of enormous importance
in maintaining the quality of the race.
Meanwhile, it seems that the unregulated increase of the population,
the indiscriminate, unquestioning protection of infant life and
of adult life also--without selection or limitation--must lead to
results which can only be described as general degeneration. How
far such a conclusion is justified, and what are possible modifying
or counteracting influences at work which may affect the future of
mankind, are questions of surpassing interest. In any case, it is
interesting to note that the cessation of selection is more complete,
and the consequent degeneration of the race would, therefore, seem
to be more probable in the higher propertied classes than in the
bare-footed toilers, whose ranks are thinned by starvation and early
death. One may well ask, “Is this really so?”
38. _The Movement, Growth, and Dwindling of Glaciers_
Last summer we were watching the gradual change of the brilliant
sunlight on the snows of Mont Blanc as the shadows crept up the
pine-covered sides of the valley of Chamonix. We noted how the highest
peak--the true summit of Mont Blanc--remained almost white and
brilliant when the somewhat lower and nearer Dome de Gouter (so often,
when clouds are about, mistaken for the true summit by tourists) had
assumed a marvellous shade of saffron-rose colour. The crevasses of
the glaciers were marked by an unearthly pale-green tint and delicate
purple hues of weird beauty were spreading over the evanescent forms
of the great snow-field, when one of the hotel guests--a citizen of
Geneva--said, “Ah, yes! Look at them whilst you may, and wonder at
them, those glaciers of the Alps. They are but the remnants, the
roots, as it were, of the vast glacier which once filled the whole of
this vale of Chamonix and spread down into the valley of the Rhone,
and ploughed out with the slow movement of its huge mass the deep
rock basin of the Lake Leman. Every year they dwindle, as they have
dwindled for ages past, and soon--perhaps not more than another 100
years hence--they will have disappeared utterly from human sight and
knowledge.” I continued to gaze at the scene, and as the night fell
and the distant details were lost to view I felt as though a venerable,
but decrepit, friend had passed from my sight, never to return. I was
rejoiced to see the glaciers still there when the morning sun showed
forth their strange opaque white and faintly green masses on the
mountain sides--stupendous outpourings, as it were, of whipped cream
tinted with pistachio-nut.
But was it true, that lament of the Genevese savant? Undoubtedly the
glaciers in many parts of the Alps have been shrinking for the last
thirty years. It is longer than that since I first saw the glaciers of
the Chamonix valley, and there is no doubt that they have shrunk up
since then, leaving acres of boulders and bare polished rock where was
the ice I formerly climbed. The glacier of Argentière, near the upper
end of the valley, is a mile or more shorter than it was; the ice caves
which we used to visit at the foot of the Mer de Glace have melted
away, and the end of the glacier is now high up above a precipitous
surface of polished rock far from the site of the little pavilion, with
its gay flag and amiable guardian, who used to exhibit the marvellous
ice cavern.
I find on looking into the matter that it is true that there has,
during the latter half of the past century, been a great dwindling
of the lower end or “snout,” a drawing back, as it were, not only of
Swiss glaciers, but of glaciers in other parts of the world--as, for
instance, in Alaska and in the Himalayas. But I cannot avoid a feeling
of satisfaction in recording the opinion of geological authorities
that, contrary to the assertion of the Swiss pessimist, there is not
any ground for believing that the present noticeable shrinking is
due to a continuous process by which the enormous glaciers of remote
ages have been incessantly reduced until now they are but rootlets or
stumps of the former masses, destined to evaporate completely under
the continued remorseless operation of increasing temperature. On the
contrary, it appears that, though there are not accurate records and
measurements as to past centuries as there will be as to present and
future years, yet there is abundant evidence that Alpine glaciers
have grown longer in some centuries and retreated in others. The
period of alternate extension and retraction has not been ascertained
with accuracy, but by some geologists it is supposed to be about
fifty years. The retraction or shrinking is not due to a continuous
increase of the temperature of the earth’s atmosphere--or of this
hemisphere--but to contending causes which operate alternately towards
increase and towards decrease when one or two hundred years are
considered. Such are the greater or less rainfall and snowfall over a
very large area, and the formation and persistence of clouds, concerned
with which are probably those varying quantities--the spots on the sun.
The simple proof that glaciers have extended and again retreated within
historic times is furnished by the fact that in some parts of the
Alpine range the retreat of a glacier has uncovered ancient miners’
excavations, which must have been worked when the glacier did not
reach the spot excavated. Subsequently the glacier advanced, and now
after some hundreds of years it has again retreated and exposed the
ice-covered borings and workings. The tradition of a glacier-enclosed
village in the Zermatt mountains, shut off from the world by the
advance of glaciers, lost and mysterious, is evidence that such advance
has been observed by the native population.
The natives who live near glaciers know that they advance and retreat,
but the fact that the whole glacier is really a slowly flowing viscous
mass--a sort of frozen but not immobile river--was only established
by scientific observation in the last century. The frozen river is
fed by the snow which falls on the higher mountain ridges, and is
squeezed into the form of ice instead of snow powder by its own weight
as it slips down the inclines, warmed by the unclouded sunshine. The
big glaciers move much more rapidly (or perhaps one should say less
slowly) in the middle than at the sides. The measurements which have
been made differ in different glaciers and in different parts of the
same glacier, and show smaller movement in winter than in summer. The
advance of the sides is retarded, as in the case of an ordinary river
of flowing water, by friction against the rocks, which enclose the
glacier as its banks enclose a river. A good average case shows a flow
downwards in summer of half a foot a day at the sides and a foot and
a half in the middle. The distance below the snow-line to which the
flowing glacier descends down a mountain gorge--before it melts away
and becomes a river of liquid water--depends, as does the rate at which
it moves, in the first place, on the temperature of the region and on
the sharpness of the slope. A glacier will flow downwards (as will a
lump of pitch) along a scarcely perceptible incline, but more slowly
than down a steeper incline, and it will, consequently, get further
down into the warm valley without altogether melting away when the
slope is steep.
But apart from these considerations, the bigger and thicker (or deeper)
the glacier, that is to say, the more snow which each year falls at
its starting-place and goes to making it, the further down will it
flow before melting away; and it is the heavy snowfall of many years
ago or of a series of years long past which has to-day reached in the
form of ice the lower end of the glacier. So, though the lower end of
the glacier may melt more quickly if the valley has become hotter,
yet the heavy snowfalls of fifty years ago may only now have reached
the valley, and may quite counterbalance the melting action of the
warmer summers. Or reverse conditions, namely, less snow and lower or
unchanged temperature in the valley, may prevail.
The Government of India has lately established a definite survey
and record of the movement of several Himalayan glaciers and of the
variation in the distance to which their “snouts” descend into the
valleys. Twelve glaciers were examined last year, and will be properly
watched in future. The Yengutsa glacier has gained about two miles in
length since Sir Martin Conway visited it in 1892; the great Hispar
glacier has slightly retreated. The Hassanabad glacier three years
ago increased its length by a rapid progress of the free “snout” of
as much as six miles in three months, and is now no longer increasing
or advancing! Many years ago it had reached its present position, and
then retreated. The rock masses carried on the ice and left in great
heaps at the point where the glacier melted away are known as terminal
“moraines,” and often serve to show the position to which the snout of
a glacier once extended--far below its present limit. A curious fact as
to the increase and shrinkage of glaciers is that of two neighbouring
glaciers, as in the case of the glacier Blanc and the glacier Noir in
Dauphiné (France), one may be advancing whilst the other is in retreat.
Further study and knowledge of the causes of these variations will
throw important light on questions of general meteorology.
Although there is no evidence to lead us to suppose that existing
glaciers are now actually in a condition of general retreat, leading
to their ultimate disappearance, yet it is one of the most certain and
interesting results of geological study that some hundred and fifty
thousand years ago the northern hemisphere was far colder than it is
now, owing partly to the same change in the inclination of the earth’s
axis to which I alluded on a former page (p. 81) as affecting the
orientation of ancient astronomical temples--a change which diminished,
when at its extreme, the effective amount of heat received from the
sun in these regions of the earth. The peculiar scratching, polishing,
and erosion of rocks, the existence of moraines, and other evidence,
prove that enormous glaciers covered the north of Europe, that England
and Scotland were in large part covered by a great ice-sheet or
glacier, and that the great valleys of Switzerland such as the Rhone
Valley and the basin of the Lake of Geneva, were filled by enormous
glaciers, which helped to mould and deepen the valleys. The present
glaciers are truly the remnants or rootlets of those enormous masses of
the glacial epoch. On such of the land surface as was not then covered
by ice, existed the hairy elephant or Siberian mammoth, the woolly
rhinoceros, wild cattle, lions, bears, hyenas, and other animals now
extinct in this part of the world. Man had made his appearance, hunted
these animals, and lived in caves. His weapons and carvings and their
bones tell us the story in no uncertain terms.
The biggest Swiss glaciers of to-day, compared to the great glacier of
the Rhone Valley, of which they are but the highest tributaries, still
surviving unmelted among the mountain-tops, are in size as a mountain
freshet is to the great stream of Loch Lomond, or as the Serpentine in
Hyde Park to the neighbouring Thames. Vast as was the great glacier of
the Rhone Valley, and immense as has been the work done by water and
ice in carving the great highway in the mountain-mass of Switzerland,
it has all been effected since the date of the formation on the
sea-bottom and the subsequent elevation of the strata which we call
“the chalk”--a deposit which comes not very far down in the series
of strata of the earth’s crust. Only 3,000ft. of deposit exist above
it, whilst below it are more than 60,000ft. of water-deposited or
“sedimentary” rocks. The huge Alps have risen since the date of the
“chalk,” for we find strata containing marine shells of the Tertiary
period at a height of 10,000ft. in those mountains. Where those shells
now are was the bottom of the sea at a comparatively recent date,
probably not more than fifty million years ago! And not only have the
Alps been raised since then from the sea level to 15,000ft. (the height
of Mont Blanc), but the huge mountain valleys and the great chasm of
the Rhone Valley many miles wide, with its floor thousands of feet
below the mountain ridges, have been scoured out. Deeper and wider it
has gradually become as it has taken shape, whilst the mountain sides
have been removed first by water and later by ice--by the great glacier
consisting of solid ice, miles wide and a thousand and more feet in
thickness. The water no longer fills the valley in solid form, but once
again rushes along as an irresistible torrent, tearing and wearing the
rock without rest or mercy, carrying it off by thousands of tons day by
day, year by year, to the plains of Provence and the deep floor of the
Mediterranean Sea.
The blue colour of the glacier ice--like that of pure water--is now
known to be due to no impurity or admixture of other substances. It
does not, as was supposed by Tyndall, owe its blueness to a dust of
finest colourless particles as do blue smoke, the blue sky, and as
do the blue eyes which have attracted the observation of naturalists
(and others) in Ireland and the North of Europe. Water, whether liquid
or solid, is blue, just as “blue copperas” is, or as “Prussian blue”
is; but light must pass through some ten or twenty feet thickness of
it to make the colour evident to our eyes. The green tint is due to
an admixture of yellow, the exact cause of which is not quite easy to
discover. Probably it is due to minute quantities of earthy matter
mixed with the surface snow.
The pressing of the high-lying snow, so as to form solid ice or
“glacier,” is concerned with the same property of snow as that
which enables us to make snow “bind” into a snowball. You cannot
make snowballs during very hard frost--the snow must be in air of a
thawing temperature at the moment it is squeezed by the hand. The hand
itself will not be warm enough to produce that temperature when the
thermometer is below freezing-point. The snow commences to melt in
the hand when one squeezes it, and then when the squeezing is stopped
the water formed quickly freezes again and cements the snow particles
together to form ice, enclosing innumerable minute bubbles. The heat
of the sun and the pressure of the weight of the snow itself take the
place in the mountains of the warmth and pressure of the human hand.
The minute air bubbles make the newest glacier-ice white and opaque,
especially when seen in a great mass; but gradually they get squeezed
together, and the glacier ice becomes first “fibrous” in appearance,
and then, after long years of pressure by its own weight, fairly clear.
Ice in great masses has the properties of a viscous body, like pitch
or soft sealing-wax, owing to the fact that wherever the solid mass
breaks its particles melt a very little and then freeze again. Under
increased pressure ice melts at a lower temperature than when it is not
subjected to pressure. When the pressure is removed the water freezes
again. Thus crushed ice or snow can be put into a “squeeze-mould” and
pressed, so as to form a solid mass of ice of any shape you may choose.
Four or five slabs of ice, placed one over the other, very soon become,
owing to this property, one continuous solid mass. White glacier ice
is so full of air bubbles as to be comparable in structure to sponge,
or, more closely, to cork. A cube of such ice exposes, owing to its
rough air-hole pitted surface, a much larger surface of contact to the
atmosphere than does a cube of perfectly smooth clear ice. Consequently
in a warm room or chamber the white ice melts much more quickly than
does the clear, and hence you should choose clear ice rather than
white ice if you wish for a block which will last.