and Fruits._--The theory that the brilliant colours of flowers and
fruits is due to the direct action of light, has been supported by
a recent writer by examples taken from the arctic instead of from
the tropical flora. In the arctic regions vegetation is excessively
rapid during the short summer, and this is held to be due to the
continuous action of light throughout the long summer days. “The
further we advance towards the north the more the leaves of plants
increase in size as if to absorb a greater proportion of the solar
rays. M. Grisebach says, that during a journey in Norway he observed
that the majority of deciduous trees had already, at the 60th degree
of latitude, larger leaves than in Germany, while M. Ch. Martins
has made a similar observation as regards the leguminous plants
cultivated in Lapland.”[26] The same writer goes on to say that all
the seeds of cultivated plants acquire a deeper colour the further
north they are grown, white haricots becoming brown or black, and
white wheat becoming brown, while the green colour of all vegetation
becomes more intense. The flowers also are similarly changed: those
which are white or yellow in central Europe becoming red or orange
in Norway. This is what occurs in the Alpine flora, and the cause is
said to be the same in both--the greater intensity of the sunlight.
In the one the light is more persistent, in the other more intense
because it traverses a less thickness of atmosphere.
[26] _Revue des Deux Mondes_, 1877. “La Vegetation dans les hautes
Latitudes,” par M. Tisserand.
Admitting the facts as above stated to be in themselves correct,
they do not by any means establish the theory founded on them; and
it is curious that Grisebach, who has been quoted by this writer
for the fact of the increased size of the foliage, gives a totally
different explanation of the more vivid colours of Arctic flowers.
He says--“We see flowers become larger and more richly coloured
in proportion as, by the increasing length of winter, insects
become rarer, and their co-operation in the act of fecundation is
exposed to more uncertain chances.” (_Vegetation du Globe_, vol.
i. p. 61--French translation.) This is the theory here adopted to
explain the colours of Alpine plants, and we believe there are many
facts that will show it to be the preferable one. The statement
that the white and yellow flowers of temperate Europe become red
or golden in the Arctic regions must we think be incorrect. By
roughly tabulating the colours of the plants given by Sir Joseph
Hooker[27] as permanently Arctic, we find among fifty species with
more or less conspicuous flowers, twenty-five white, twelve yellow,
eight purple or blue, three lilac, and two red or pink; showing a
very similar proportion of white and yellow flowers to what obtains
further south.
[27] “On the Distribution of Arctic Plants,” _Linn. Trans._ vol.
xxiii. (1862.)
We have, however, a remarkable flora in the Southern Hemisphere which
affords a crucial test of the theory of greater intensity of light
being the direct cause of brilliantly-coloured flowers. The Auckland
and Campbell’s Islands south of New Zealand, are in the same latitude
as the middle and the south of England, and the summer days are
therefore no longer than with us. The climate though cold is very
uniform, and the weather “very rainy and stormy.” It is evident,
then, that there can be no excess of sunshine above what we possess;
yet in a very limited flora there are a number of flowers which--Sir
Joseph Hooker states--are equal in brilliancy to the Arctic flora.
These consist of brilliant gentians, handsome veronicas, large and
magnificent Compositæ with purple flowers, bright ranunculi, showy
Umbelliferæ, and the golden flowered _Chrysobactron Rossii_, one of
the finest of the Asphodeleæ.[28] All these fine plants, it must be
remembered, are peculiar to these islands, and have therefore been
developed under the climatal conditions that prevail there; and as
we have no reason to suppose that these conditions have undergone
any recent change we may be quite sure that an excess of light
has had nothing to do with the development of these exceptionally
bright and handsome flowers. Unfortunately we have no information
as to the insects of these islands, but from their scarcity in New
Zealand we can hardly expect them to be otherwise than very scarce.
There are however two species of honey-sucking birds (Prosthemadera
and Anthornis) as well as a small warbler (Myiomoira), and we may be
pretty sure that the former at least visit these large and handsome
flowers, and so effect their fertilization. The most abundant tree
on the islands is a species of Metrosideros, and we know that trees
of this genus are common in the Pacific islands, where they are
almost certainly fertilized by the same family of Meliphagidæ or
honey-sucking birds.
[28] Coloured figures of all these plants are given in the _Flora
Antarctica_, vol. i.
I have now concluded this sketch of the general phenomena of colour
in the organic world. I have shown reasons for believing that its
presence, in some of its infinitely-varied hues, is more probable
than its absence; and that variation of colour is an almost necessary
concomitant of variation of structure, of development, and of growth.
It has also been shown how colour has been appropriated and modified
both in the animal and vegetable worlds for the advantage of the
species in a great variety of ways, and that there is no need to
call in the aid of any other laws than those of organic development
and “natural selection” to explain its countless modifications.
From the point of view here taken it seems at once improbable and
unnecessary that the lower animals should have the same delicate
appreciation of the infinite variety and beauty--of the delicate
contrasts and subtle harmonies of colour, which are possessed by
the more intellectual races of mankind, since even the lower human
races do not possess it. All that seems required in the case of
animals, is a perception of _distinctness_ or _contrast_ of colours;
and the dislike of so many creatures to scarlet may perhaps be due
to the rarity of that colour in nature, and to the glaring contrast
it offers to the sober greens and browns which form the general
clothing of the earth’s surface, though it may also have a direct
irritating effect on the retina.
The general view of the subject now given must convince us that,
so far from colour being--as it has sometimes been thought to
be--unimportant, it is intimately connected with the very existence
of a large proportion of the species of the animal and vegetable
worlds. The gay colours of the butterfly and of the alpine flower
which it unconsciously fertilizes while seeking for its secreted
honey, are each beneficial to its possessor, and have been shown to
be dependent on the same class of general laws as those which have
determined the form, the structure, and the habits of every living
thing. The complex laws and unexpected relations which we have seen
to be involved in the production of the special colours of flower,
bird, and insect, must give them an additional interest for every
thoughtful mind; while the knowledge that, in all probability, each
style of coloration, and sometimes the smallest details, have a
meaning and a use, must add a new charm to the study of nature.
ON THE ORIGIN OF THE COLOUR-SENSE.
Throughout the preceding discussion we have accepted the subjective
phenomena of colour--that is, our perception of varied hues and
the mental emotions excited by them, as ultimate facts needing
no explanation. Yet they present certain features well worthy of
attention, a brief consideration of which will form a fitting sequel
to the present essay.
The perception of colour seems, to the present writer, the most
wonderful and the most mysterious of our sensations. Its extreme
diversities and exquisite beauties seem out of proportion to the
causes that are supposed to have produced them, or the physical
needs to which they minister. If we look at pure tints of red,
green, blue, and yellow, they appear so absolutely contrasted
and unlike each other, that it is almost impossible to believe
(what we nevertheless know to be the fact) that the rays of light
producing these very distinct sensations differ only in wave-length
and rate of vibration; and that there is from one to the other a
continuous series and gradation of such vibrating waves. The positive
diversity we see in them must then depend upon special adaptations
in ourselves; and the question arises--for what purpose have our
visual organs and mental perceptions become so highly specialised
in this respect?
When the sense of sight was first developed in the animal kingdom,
we can hardly doubt that what was perceived was light only, and its
more or less complete withdrawal. As the sense became perfected,
more delicate gradations of light and shade would be perceived;
and there seems no reason why a visual capacity might not have been
developed as perfect as our own, or even more so in respect of light
and shade, but entirely insensible to differences of colour except
in so far as these implied a difference in the quantity of light.
The world would in that case appear somewhat as we see it in good
stereoscopic photographs; and we all know how exquisitely beautiful
such pictures are, and how completely they give us all requisite
information as to form, surface-texture, solidity, and distance,
and even to some extent as to colour; for almost all colours are
distinguishable in a photograph by some differences of tint, and
it is quite conceivable that visual organs might exist which would
differentiate what we term colour by delicate gradations of some one
characteristic neutral tint. Now such a capacity of vision would
be simple as compared with that which we actually possess; which,
besides distinguishing infinite gradations of the _quantity_ of
light, distinguishes also, by a totally distinct set of sensations,
gradations of _quality_, as determined by differences of wave-lengths
or rate of vibration. At what grade in animal development this new
and more complex sense first began to appear we have no means of
determining. The fact that the higher vertebrates, and even some
insects, distinguish what are to us diversities of colour, by no
means proves that their _sensations_ of colour bear any resemblance
whatever to ours. An insect’s capacity to distinguish red from blue
or yellow may be (and probably is) due to perceptions of a totally
distinct nature, and quite unaccompanied by any of that sense of
enjoyment or even of radical distinctness which pure colours excite
in us. Mammalia and birds, whose structure and emotions are so
similar to our own, do probably receive somewhat similar impressions
of colour; but we have no evidence to show that they experience
pleasurable emotions from colour itself, when not associated with
the satisfaction of their wants or the gratification of their
passions.
The primary necessity which led to the development of the sense of
colour, was probably the need of distinguishing objects much alike
in form and size, but differing in important properties;--such as
ripe and unripe, or eatable and poisonous fruits; flowers with honey
or without; the sexes of the same or of closely allied species.
In most cases the strongest contrast would be the most useful,
especially as the colours of the objects to be distinguished would
form but minute spots or points when compared with the broad masses
of tint of sky, earth, or foliage against which they would be set.
Throughout the long epochs in which the sense of sight was being
gradually developed in the higher animals, their visual organs
would be mainly subjected to two groups of rays--the green from
vegetation, and the blue from the sky. The immense preponderance of
these over all other groups of rays would naturally lead the eye
to become specially adapted for their perception; and it is quite
possible that at first these were the only kinds of light-vibrations
which could be perceived at all. When the need for differentiation
of colour arose, rays of greater and of smaller wave-lengths would
necessarily be made use of to excite the new sensations required;
and we can thus understand why green and blue form the central
portion of the visible spectrum, and are the colours which are most
agreeable to us in large surfaces; while at its two extremities
we find yellow, red, and violet--colours which we best appreciate
in smaller masses, and when contrasted with the other two, or with
light neutral tints. We have here probably the foundations of a
natural theory of harmonious colouring, derived from the order
in which our colour-sensations have arisen and the nature of the
emotions with which the several tints have been always associated.
The agreeable and soothing influence of green light may be in
part due to the green rays having little heating power; but this
can hardly be the chief cause, for the blue and violet, though
they contain less heat, are not generally felt to be so cool and
sedative. But when we consider how dependent are all the higher
animals on vegetation, and that man himself has been developed in
the closest relation to it, we shall find, probably, a sufficient
explanation. The green mantle with which the earth is overspread
caused this one colour to predominate over all others that meet our
sight, and to be almost always associated with the satisfaction
of human wants. Where the grass is greenest, and vegetation most
abundant and varied, there has man always found his most suitable
dwelling-place. In such spots hunger and thirst are unknown, and the
choicest productions of nature gratify the appetite and please the
eye. In the greatest heats of summer, coolness, shade, and moisture
are found in the green forest glades; and we can thus understand
how our visual apparatus has become especially adapted to receive
pleasurable and soothing sensations from this class of rays.
_Supposed increase of Colour-perception within the Historical
Period._--Some writers believe that our power of distinguishing
colours has increased even in historical times. The subject has
attracted the attention of German philologists, and I have been
furnished by a friend with some notes from a work of the late Lazarus
Geiger, entitled, _Zur Entwickelungsgeschichte der Menschheit_
(Stuttgart, 1871). According to this writer it appears that the
_colour_ of grass and foliage is never alluded to as a beauty in the
Vedas or the Zendavesta, though these productions are continually
extolled for other properties. Blue is described by terms denoting
sometimes green, sometimes black, showing that it was hardly
recognised as a distinct colour. The _colour_ of the sky is never
mentioned in the Bible, the Vedas, the Homeric poems, or even in
the Koran. The first distinct allusion to it known to Geiger is
in an Arabic work of the ninth century. “Hyacinthine locks” are
black locks, and Homer calls iron “violet-coloured.” Yellow was
often confounded with green; but, along with red, it was one of
the earliest colours to receive a distinct name. Aristotle names
three colours in the rainbow--red, yellow, and green. Two centuries
earlier Xenophanes had described the rainbow as purple, reddish,
and yellow. The Pythagoreans admitted four primary colours--white,
black, red, and yellow; the Chinese the same, with the addition of
green.
Simultaneously with the first publication of this essay in
_Macmillan’s Magazine_, there appeared in the _Nineteenth Century_ an
article by Mr. Gladstone on the Colour-sense, chiefly as exhibited
in the poems of Homer. He shows that the few colour-terms used by
Homer are applied to such different objects that they cannot denote
colours only, as we perceive and differentiate them; but seem more
applicable to different intensities of light and shade. Thus, to
give one example, the word _porphureos_ is applied to clothing, to
the rainbow, to blood, to a cloud, to the sea, and to death; and
no one meaning will suit all these applications except comparative
darkness. In other cases the same thing has many different epithets
applied to it according to its different aspects or conditions; and
as the colours of objects are generally indicated in ancient writings
by comparative rather than by abstract terms,--as wine-colour,
fire-colour, bronze-colour, &c.--it becomes still more difficult
to determine in any particular case what colour was really meant.
Mr. Gladstone’s general conclusion is, that the archaic man had a
positive perception only of degrees of light and darkness, and that
in Homer’s time he had advanced to the imperfect discrimination of
red and yellow, but no further; the green of grass and foliage or
the blue of the sky being never once referred to.
These curious facts cannot, however, be held to prove so recent an
origin for colour-sensations as they would at first sight appear to
do, because we have seen that both flowers and fruits have become
diversely coloured in adaptation to the visual powers of insects,
birds, and mammals. Red, being a very common colour of ripe fruits
which attract birds to devour them and thus distribute their seeds,
we may be sure that the contrast of red and green is to them very
well marked. It is indeed just possible that birds may have a more
advanced development of the colour-sense than mammals, because the
teeth of the latter commonly grind up and destroy the seeds of the
larger fruits and nuts which they devour, and which are not usually
coloured; but the irritating effect of bright colours on some of
them does not support this view. It seems most probable therefore
that man’s _perception_ of colour in the time of Homer was little
if any inferior to what it is now, but that, owing to a variety of
causes, no precise _nomenclature_ of colours had become established.
One of these causes probably was, that the colours of the objects
of most importance, and those which were most frequently referred
to in songs and poems, were uncertain and subject to variation.
Blood was light or dark red, or when dry, blackish; iron was grey
or dark or rusty; bronze was shining or dull; foliage was of all
shades of yellow, green, or brown; and horses or cattle had no one
distinctive colour. Other objects, as the sea, the sky, and wine,
changed in tint according to the light, the time of day, and the mode
of viewing them; and thus colour, indicated at first by reference
to certain coloured objects, had no fixity. Things which had more
definite and purer colours--as certain species of flowers, birds,
and insects--were probably too insignificant or too much despised
to serve as colour-terms; and even these often vary, either in the
same or in allied species, in a manner which would render their use
unsuitable. Colour-names, being abstractions, must always have been
a late development in language, and their comparative unimportance
in an early state of society and of the arts would still further
retard their appearance; and this seems quite in accordance with
the various facts set forth by Mr. Gladstone and the other writers
referred to. The fact that colour-blindness is so prevalent even
now, is however an indication that the fully developed colour-sense
is not of primary importance to man. If it had been so, natural
selection would long ago have eliminated the disease itself, and
its tendency to recur would hardly be so strong as it appears to
be.
_Concluding Remarks on the Colour-sense._--The preceding
considerations enable us to comprehend, both why a perception of
difference of colour has become developed in the higher animals,
and also why colours require to be presented or combined in varying
proportions in order to be agreeable to us. But they hardly seem to
afford a sufficient explanation, either of the wonderful contrasts
and total unlikeness of the sensations produced in us by the chief
primary colours, or of the exquisite charm and pleasure we derive
from colour itself, as distinguished from variously-coloured objects,
in the case of which association of ideas comes into play. It is
hardly conceivable that the material _uses_ of colour to animals and
to ourselves, required such very distinct and powerfully-contrasted
sensations; and it is still less conceivable that a sense of delight
in colour _per se_ should have been necessary for our utilization
of it.
The emotions excited by colour and by music, alike, seem to
rise above the level of a world developed on purely utilitarian
principles.
VII.
BY-PATHS IN THE DOMAIN OF BIOLOGY:
BEING AN ADDRESS DELIVERED TO THE BIOLOGICAL SECTION OF THE BRITISH
ASSOCIATION, (GLASGOW, SEPTEMBER 6TH, 1876,) AS PRESIDENT OF THE
SECTION.
Introductory Remarks--ON SOME RELATIONS OF LIVING THINGS TO
THEIR ENVIRONMENT--The Influence of Locality on Colour in
Butterflies and Birds--Sense-perception influenced by Colour of
the Integuments--Relations of Insular Plants and Insects--RISE
AND PROGRESS OF MODERN VIEWS AS TO THE ANTIQUITY AND ORIGIN
OF MAN--Indications of Man’s extreme Antiquity--Antiquity of
Intellectual Man--Sculptures on Easter-Island--North American
Earthworks--The Great Pyramid--Conclusion.
The range of subjects comprehended within the domain of Biology is
so wide, and my own acquaintance with them so imperfect, that it is
not in my power to lay before you any general outline of the recent
progress of the biological sciences. Neither do I feel competent to
give you a summary of the present status of any one of the great
divisions of our science, such as Anatomy, Physiology, Embryology,
Histology, Classification, or Evolution--Philology, Ethnology, or
Prehistoric Archæology; but there are fortunately several outlying
and more or less neglected subjects to which I have for some time
had my attention directed, and which I hope will furnish matter
for a few observations, of some interest to biologists and at the
same time not unintelligible to the less scientific members of the
Association who may honour us with their presence.
The subjects I first propose to consider have no general name, and
are not easily grouped under a single descriptive heading; but they
may be compared with that recent development of a sister science
which has been termed surface-geology or Earth-sculpture. In the
older geological works we learnt much about strata, and rocks, and
fossils, their superposition, contortions, chemical constitution,
and affinities, with some general notions of how they were formed
in the remote past; but we often came to the end of the volume no
whit the wiser as to how and why the surface of the earth came to
be so wonderfully and beautifully diversified; we were not told
why some mountains are rounded and others precipitous; why some
valleys are wide and open, others narrow and rocky; why rivers so
often pierce through mountain-chains; why mountain-lakes are often
so enormously deep; whence came the gravel, and drift, and erratic
blocks so strangely spread over wide areas while totally absent
from other areas equally extensive. So long as these questions
were almost ignored, geology could hardly claim to be a complete
science, because, while professing to explain how the crust of the
earth came to be what it is, it gave no intelligible account of
many phenomena presented by its surface. But of late years these
surface-phenomena have been assiduously studied; the marvellous
effects of denudation and glacial action in giving the final touches
to the actual contour of the earth’s surface, and their relation
to climatic changes and the antiquity of man, have been clearly
traced, thus investing geology with a new and popular interest,
and at the same time elucidating many of the phenomena presented
in the older formations.