so a surface-biology was wanted to make the science of living things
more complete and more generally interesting, by applying the results
arrived at by special workers to the interpretation of those external
and prominent features whose endless variety and beauty constitute
the charm which attracts us to the contemplation or to the study of
nature. We have the descriptive zoologist, for example, who gives
us the external characters of animals; the anatomist studies their
internal structure; the histologist makes known the nature of their
component tissues; the embryologist patiently watches the progress
of their development; the systematist groups them into classes and
orders, families, genera, and species; while the field-naturalist
studies for us their food and habits and general economy. But,
till quite recently, none of these earnest students nor all of
them combined, could answer satisfactorily, or even attempted to
answer, many of the simplest questions concerning the external
characters and general relations of animals and plants. Why are
flowers so wonderfully varied in form and colour? what causes the
Arctic fox and the ptarmigan to turn white in winter? why are there
no elephants in America and no deer in Australia? why are closely
allied species rarely found together? why are male animals so
frequently bright-coloured? why are extinct animals so often larger
than those which are now living? what has led to the production of
the gorgeous train of the peacock and of the two kinds of flower
in the primrose? The solution of these and a hundred other problems
of like nature was rarely approached by the old method of study,
or if approached was only the subject of vague speculation. It is
to the illustrious author of the _Origin of Species_ that we are
indebted for teaching us how to study nature as one great, compact,
and beautifully-adjusted system. Under the touch of his magic wand
the countless isolated facts of internal and external structure
of living things--their habits, their colours, their development,
their distribution, their geological history,--all fell into their
approximate places; and although, from the intricacy of the subject
and our very imperfect knowledge of the facts themselves, much still
remains uncertain, yet we can no longer doubt that even the minutest
and most superficial peculiarities of animals and plants either,
on the one hand, are or have been useful to them, or, on the other
hand, have been developed under the influence of general laws, which
we may one day understand to a much greater extent than we do at
present. So great is the alteration effected in our comprehension
of nature by the study of variation, inheritance, cross-breeding,
competition, distribution, protection, and selection--showing, as
they often do, the meaning of the most obscure phenomena and the
mutual dependence of the most widely-separated organisms--that it
can only be fitly compared with the analogous alteration produced
in our conception of the universe by Newton’s grand discovery of
the law of gravitation.
I know it will be said (and is said), that Darwin is too highly
rated, that some of his theories are wholly and others partially
erroneous, and that he often builds a vast superstructure on a very
uncertain basis of doubtfully interpreted facts. Now, even admitting
this criticism to be well founded--and I myself believe that to a
limited extent it is so--I nevertheless maintain that Darwin is
not and cannot be too highly rated; for his greatness does not at
all depend upon his being infallible, but on his having developed,
with rare patience and judgment, a new system of observation and
study, guided by certain general principles which are almost as
simple as gravitation and as wide-reaching in their effects. And
if other principles should hereafter be discovered, or if it be
proved that some of his subsidiary theories are wholly or partially
erroneous, this very discovery can only be made by following in
Darwin’s steps, by adopting the method of research which he has
taught us, and by largely using the rich stores of material which
he has collected. The _Origin of Species_, and the grand series of
works which have succeeded it, have revolutionized the study of
biology; they have given us new ideas and fertile principles; they
have infused life and vigour into our science, and have opened up
hitherto unthought-of lines of research on which hundreds of eager
students are now labouring. Whatever modifications some of his
theories may require, Darwin must none the less be looked up to as
the founder of philosophical biology.
As a small contribution to this great subject, I propose now to
call your attention to some curious relations of organisms to their
environment, which seem to me worthy of more systematic study than
has hitherto been given them. The points I shall more especially
deal with are--the influence of locality, or of some unknown
local causes, in determining the colours of insects, and, to a
less extent, of birds; and the way in which certain peculiarities
in the distribution of plants may have been brought about by their
dependence on insects. The latter part of my address will deal with
the present state of our knowledge as to the antiquity and early
history of mankind.
ON SOME RELATIONS OF LIVING THINGS TO THEIR ENVIRONMENT.
Of all the external characters of animals, the most beautiful, the
most varied, and the most generally attractive are the brilliant
colours and strange yet often elegant markings with which so many of
them are adorned. Yet of all characters this is the most difficult
to bring under the laws of utility or of physical connection. Mr.
Darwin--as you are well aware--has shown how wide is the influence
of sex on the intensity of coloration; and he has been led to
the conclusion that active or voluntary sexual selection is one
of the chief causes, if not the chief cause, of all the variety
and beauty of colour we see among the higher animals. This is one
of the points on which there is much divergence of opinion even
among the supporters of Mr. Darwin, and one as to which I myself
differ from him. I have argued, and still believe, that the need
of protection is a far more efficient cause of variation of colour
than is generally suspected; but there are evidently other causes at
work, and one of these seems to be an influence depending strictly
on locality, whose nature we cannot yet understand, but whose
effects are everywhere to be seen when carefully searched for.
Although the careful experiments of Sir John Lubbock have shown that
insects can distinguish colours--as might have been inferred from
the brilliant colours of the flowers which are such an attraction
to them--yet we can hardly believe that their appreciation and love
of distinctive colours is so refined as to guide and regulate their
most powerful instinct--that of reproduction. We are therefore led
to seek some other cause for the varied colours that prevail among
insects; and as this variety is most conspicuous among butterflies--a
group perhaps better known than any other--it offers the best means
of studying the subject. The variety of colour and marking among
these insects is something marvellous. There are probably about ten
thousand different kinds of butterflies now known, and about half
of these are so distinct in colour and marking that they can be
readily distinguished by this means alone. Almost every conceivable
tint and pattern is represented, and the hues are often of such
intense brilliance and purity as can be equalled by neither birds
nor flowers.
Any help to a comprehension of the causes which may have concurred
in bringing about so much diversity and beauty must be of value; and
this is my excuse for laying before you the more important cases
I have met with of a connection between colour and locality.
_The influence of Locality on Colour in Butterflies and Birds._--Our
first example is from tropical Africa, where we find two unrelated
groups of butterflies belonging to two very distinct families
(Nymphalidæ and Papilionidæ) characterized by a prevailing
blue-green colour not found in any other continent.[29] Again, we
have a group of African Pieridæ which are white or pale yellow with
a marginal row of bead-like black spots; and in the same country
one of the Lycænidæ (_Leptena erastus_) is coloured so exactly like
these that it was at first described as a species of _Pieris_. None
of these four groups are known to be in any way specially protected,
so that the resemblance cannot be due to protective mimicry.
[29] Romaleosoma and Euryphene (Nymphalidæ), _Papilio zalmoxis_
and several species of the Nireus-group (Papilionidæ).
In South America we have far more striking cases; for in the three
subfamilies Danainæ, Acræinæ, and Heliconiinæ, all of which are
specially protected, we find identical tints and patterns reproduced,
often in the greatest detail, each peculiar type of coloration
being characteristic of separate geographical subdivisions of
the continent. Nine very distinct genera are implicated in these
parallel changes--Lycorea, Ceratinia, Mechanitis, Ithomia, Melinæa,
Tithorea, Acræa, Heliconius, and Eueides, groups of three or four
(or even five) of them appearing together in the same livery in
one district, while in an adjoining district most or all of them
undergo a simultaneous change of coloration or of marking. Thus in
the genera Ithomia, Mechanitis, and Heliconius we have species with
yellow apical spots in Guiana, all represented by allied species
with white apical spots in South Brazil. In Mechanitis, Melinæa, and
Heliconius, and sometimes in Tithorea, the species of the Southern
Andes (Bolivia and Peru) are characterized by an orange and black
livery, while those of the Northern Andes (New Granada) are almost
always orange-yellow and black. Other changes of a like nature,
which it would be tedious to enumerate but which are very striking
when specimens are examined, occur in species of the same groups
inhabiting these same localities, as well as Central America and the
Antilles. The resemblance thus produced between widely different
insects is sometimes general, but often so close and minute that
only a critical examination of structure can detect the difference
between them. Yet this can hardly be true mimicry, because all
are alike protected by the nauseous secretion which renders them
unpalatable to birds.
In another series of genera (Catagramma, Callithea, and Agrias) all
belonging to the Nymphalidæ, we have the most vivid blue ground,
with broad bands of orange, crimson or a different tint of blue or
purple, exactly reproduced in corresponding, yet unrelated species,
occurring in the same locality; yet, as none of these groups are
known to be specially protected, this can hardly be true mimicry.
A few species of two other genera in the same country (Eunica and
Siderone) also reproduce the same colours, but with only a general
resemblance in the markings. Yet again, in tropical America we have
species of Apatura which, sometimes in both sexes, sometimes in the
female only, exactly imitate the peculiar markings of another genus
(Heterochroa) confined to America: here, again, neither genus is
protected, and the similarity must be due to unknown local causes.
But it is among islands that we find some of the most striking
examples of the influence of locality on colour, generally in the
direction of paler, but sometimes of darker and more brilliant hues,
and often accompanied by an unusual increase of size. Thus in the
Moluccas and New Guinea we have several Papilios (_P. euchenor_,
_P. ormenus_, and _P. tydeus_) distinguished from their allies by
a much paler colour, especially in the females which are almost
white. Many species of Danais (forming the subgenus Ideopsis) are
also very pale. But the most curious are the Euplœas, which in the
larger islands are usually of rich dark colours, while in the small
islands of Banda, Ké, and Matabello at least three species not
nearly related to each other (_E. hoppferi_, _E. euripon_, and _E.
assimilata_) are all broadly banded or suffused with white, their
allies in the larger islands being all very much darker. Again, in
the genus Diadema, belonging to a distinct family, three species
from the small Aru and Ké islands (_D. deois_, _D. hewitsonii_,
and _D. polymena_) are all more conspicuously white-marked than
their representatives in the larger islands. In the beautiful genus
Cethosia, a species from the small island of Waigiou (_C. cyrene_)
is the whitest of the genus. Prothoë is represented by a blue
species in the continental island of Java, while those inhabiting
the ancient insular groups of the Moluccas and New Guinea are all
pale yellow or white. The genus Drusilla, almost confined to these
islands, comprises many species which are all very pale; while in
the small island of Waigiou is found a very distinct genus, Hyantis,
which, though differing completely in the neuration of the wings,
has exactly the same pale colours and large ocellated spots as
Drusilla.
Equally remarkable is the increase of size in some islands. The
small island of Amboina produces larger butterflies than any of
the much larger islands which surround it. This is the case with at
least a dozen butterflies belonging to many distinct genera,[30]
so that it is impossible to attribute the fact to other than some
local influence. In Celebes, as I have elsewhere pointed out,[31] we
have a peculiar form of wing and much larger size running through
a whole series of distinct butterflies; and this seems to take the
place of any speciality in colour.
[30] _Ornithoptera priamus_, _O. helena_, _Papilio deiphobus_, _P.
ulysses_, _P. gambrisius_, _P. codrus_, _Iphias leucippe_, _Euplœa
prothoë_, _Hestia idea_, _Athyma jocaste_, _Diadema pandarus_,
_Nymphalis pyrrhus_, _N. euryalus_, _Drusilla jairus_.
[31] “Contributions to the Theory of Natural Selection,” pp. 168-173.
In a very small collection of insects recently brought from
Duke-of-York Island (situated between New Britain and New Ireland)
are several of remarkably white or pale coloration. A species of
Euplœa is the whitest of all known species of that extensive genus;
while a beautiful diurnal moth is much whiter than its ally in the
larger island of New Guinea. There is also a magnificent longicorn
beetle almost entirely of an ashy white colour.[32]
[32] These insects are described and figured in the “Proceedings of
the Zoological Society,” for 1877, p. 139. Their names are _Euplœa
browni_, _Alcides aurora_, and _Batocera browni_.
From the Fiji Islands we have comparatively few butterflies; but
there are several species of Diadema of unusually pale colours,
some almost white.
The Philippine Islands seem to have the peculiarity of developing
metallic colours. We find there at least three species of Euplœa[33]
not closely related, and all of more intense metallic lustre than
their allies in other islands. Here also we have one of the large
yellow Ornithopteræ (_O. magellanus_), whose hind wings glow with
an intense opaline lustre not found in any other species of the
entire group; and an Adolias[34] is larger and of more brilliant
metallic colouring than any other species in the archipelago. In
these islands also we find the extensive and wonderful genus of
weevils (Pachyrhynchus), which in their brilliant metallic colouring
surpass anything found in the whole eastern hemisphere, if not in
the whole world.
[33] _Euplœa hewitsonii_, _E. diocletiana_, _E. lætifica_.
[34] _Adolias calliphorus._
In the Andaman Islands in the Bay of Bengal there are a considerable
number of peculiar species of butterflies differing slightly from
those on the continent, and generally in the direction of paler or
more conspicuous colouring. Thus two species of Papilio which on the
continent have the tails black, in their Andaman representatives
have them either red or white-tipped.[35] Another species[36] is
richly blue-banded where its allies are black; while three species
of distinct genera of Nymphalidæ[37] all differ from their allies
on the continent in being of excessively pale colours as well as
of somewhat larger size.
[35] _Papilio rhodifer_ (near _P. doubledayi_), and _Papilio
charicles_ (near _P. memnon_).
[36] _Papilio mayo._
[37] _Euplœa andamanensis_, _Cethosia biblis_, _Cyrestis cocles_.
In Madagascar we have the very large and singularly white-spotted
_Papilio antenor_; while species of three other genera[38] are very
white or conspicuous as compared with their continental allies.
[38] _Danais nossima_, _Melanitis massoura_, _Diadema dexithea_.
Passing to the West-Indian Islands and Central America (which latter
country has formed a group of islands in very recent times) we have
similar indications. One of the largest of the Papilios inhabits
Jamaica,[39] while another, the largest of its group, is found in
Mexico.[40] Cuba has two of the same genus whose colours are of
surpassing brilliancy;[41] while the fine genus Clothilda--confined
to the Antilles and Central America--is remarkable for its rich
and showy colouring.
[39] _Papilio homerus._
[40] _P. daunus._
[41] _P. gundlachianus_, _P. villiersi_.
Persons who are not acquainted with the important structural
differences that distinguish these various genera of butterflies can
hardly realize the importance and the significance of such facts
as I have now detailed. It may be well, therefore, to illustrate
them by supposing parallel cases to occur among the Mammalia. We
might have, for example, in Africa, the gnus, the elands, and the
buffaloes, all coloured and marked like zebras, stripe for stripe
over the whole body exactly corresponding. So the hares, marmots,
and squirrels of Europe might be all red with black feet, while the
corresponding species of Central Asia were all yellow with black
heads. In North America we might have raccoons, squirrels, and
opossums, in particoloured livery of white and black, so as exactly
to resemble the skunk of the same country; while in South America
they might be black with a yellow throat-patch, so as to resemble
with equal closeness the tayra of the Brazilian forests. Were such
resemblances to occur in anything like the number and with the
wonderful accuracy of imitation met with among the Lepidoptera,
they would certainly attract universal attention among naturalists,
and would lead to the exhaustive study of the influence of local
causes in producing such startling results.
One somewhat similar case does indeed occur among the Mammalia, two
singular African animals, the Aard-wolf (Proteles) and the hyæna-dog
(Lycaon), both strikingly resembling hyænas in their general form
as well as in their spotted markings. Belonging as they all do to
the Carnivora, though to three distinct families, it seems quite
an analogous case to those we have imagined; but as the Aard-wolf
and the hyæna-dog are both weak animals compared with the hyæna,
the resemblance may be useful, and in that case would come under
the head of mimicry. This seems the more probable because, as a
rule, the colours of the Mammalia are protective, and are too
little varied to allow of the influence of local causes producing
any well-marked effects.
When we come to birds, however, the case is different; for although
they do not exhibit such distinct marks of the influence of locality
as do butterflies--probably because the causes which determine colour
are in their case more complex--yet there are distinct indications
of some effect of the kind, and we must devote some little time to
their consideration.
One of the most curious cases is that of the parrots of the
West-Indian Islands and Central America, several of which have
white heads or foreheads, occurring in two distinct genera,[42]
while none of the more numerous parrots of South America are so
coloured. In the small island of Dominica we have a very large and
richly-coloured parrot (_Chrysotis augusta_) corresponding to the
large and richly-coloured butterfly (_Papilio homerus_) of Jamaica.
[42] _Pionus albifrons_ and _Chrysotis senilis_ (C. America),
_Chrysotis sallæi_ (Hayti).
The Andaman Islands are equally remarkable, at least six of the
peculiar birds differing from their continental allies in being
much lighter, and sometimes with a large quantity of pure white in
the plumage,[43] exactly corresponding to what occurs among the
butterflies.
[43] _Kittacincla albiventris_, _Geocichla albigularis_, _Sturnia
andamanensis_, _Hyloterpe grisola_ var., _Ianthœnas palumboides_,
_Osmotreron chloroptera_.
In the Philippines this is not so marked a feature; yet we have here
the only known white-breasted king-crow (_Dicrurus mirabilis_);
the newly discovered _Eurylæmus steerii_, wholly white beneath;
three species of Diceum, all white beneath; several species of
Parus, largely white-spotted; while many of the pigeons have light
ashy tints. The birds generally, however, have rich dark colours,
similar to those which prevail among the butterflies.
In Celebes we have a swallow-shrike and a peculiar small crow
allied to the jackdaw,[44] whiter than any of their allies in the
surrounding islands; but otherwise the colours of the birds call
for no special remark.
[44] _Artamus monachus_, _Corvus advena_.
In Timor and Flores we have white-headed pigeons,[45] and a
long-tailed flycatcher almost entirely white.[46]
[45] _Ptilopus cinctus_, _P. albocinctus_.
[46] _Tchitrea affinis_, var.
In Duke-of-York Island east of New Guinea we find that the four new
species figured in the “Proceedings of the Zoological Society,” for
1877, are _all_ remarkable for the unusual quantity of white in their
plumage. They consist of a flycatcher, a diceum, a wood-swallow, and
a ground pigeon;[47] all equalling if not surpassing their nearest
allies in whiteness, although some of these, from the Philippines,
Moluccas and Celebes, are sufficiently remarkable in this respect.
[47] _Monarcha verticalis_, _Diceum eximium_, _Artamus insignis_,
_Phlogœnas johannæ_.
In the small Lord Howe’s Island we have the recently extinct white
rail (_Notornis alba_), remarkably contrasting with its allies in
the larger islands of New Zealand.
We cannot, however, lay any stress on isolated examples of white
colour, since these occur in most of the great continents; but where
we find a series of species of distinct genera all differing from
their continental allies in a whiter coloration, as in the Andaman
Islands, Duke-of-York Island, and the West Indies, and, among
butterflies, in the smaller Moluccas, the Andamans, and Madagascar,
we cannot avoid the conclusion that in these insular localities
some general cause is at work.
There are other cases, however, in which local influences seem
to favour the production or preservation of intense crimson or a
very dark coloration. Thus in the Moluccas and New Guinea alone we
have bright red parrots belonging to two distinct families,[48]
and which therefore most probably have been independently produced
or preserved by some common cause. Here, too, and in Australia we
have black parrots and pigeons;[49] and it is a most curious and
suggestive fact that in another insular subregion--that of Madagascar
and the Mascarene Islands--these same colours reappear in the same
two groups.[50]
[48] _Lorius_, _Eos_ (Trichoglossidæ), _Eclectus_ (Palæornithidæ).
[49] _Microglossus_, _Calyptorhynchus_, _Turacœna_.
[50] _Coracopsis_, _Alectrœnas_.