Copyright
Charles Darwin.

The Voyage of the Beagle online

. (page 39 of 51)
Online LibraryCharles DarwinThe Voyage of the Beagle → online text (page 39 of 51)
Font size
QR-code for this ebook


lizard was eating at the other end; and afterwards the little bird
with the utmost indifference hopped on the back of the reptile.

I opened the stomachs of several, and found them full of vegetable
fibres and leaves of different trees, especially of an acacia. In
the upper region they live chiefly on the acid and astringent
berries of the guayavita, under which trees I have seen these
lizards and the huge tortoises feeding together. To obtain the
acacia-leaves they crawl up the low stunted trees; and it is not
uncommon to see a pair quietly browsing, whilst seated on a branch
several feet above the ground. These lizards, when cooked, yield a
white meat, which is liked by those whose stomachs soar above all
prejudices. Humboldt has remarked that in intertropical South
America all lizards which inhabit dry regions are esteemed
delicacies for the table. The inhabitants state that those which
inhabit the upper damp parts drink water, but that the others do
not, like the tortoises, travel up for it from the lower sterile
country. At the time of our visit, the females had within their
bodies numerous, large, elongated eggs, which they lay in their
burrows: the inhabitants seek them for food.

These two species of Amblyrhynchus agree, as I have already stated,
in their general structure, and in many of their habits. Neither
have that rapid movement, so characteristic of the genera Lacerta
and Iguana. They are both herbivorous, although the kind of
vegetation on which they feed is so very different. Mr. Bell has
given the name to the genus from the shortness of the snout:
indeed, the form of the mouth may almost be compared to that of the
tortoise: one is led to suppose that this is an adaptation to their
herbivorous appetites. It is very interesting thus to find a
well-characterised genus, having its marine and terrestrial
species, belonging to so confined a portion of the world. The
aquatic species is by far the most remarkable, because it is the
only existing lizard which lives on marine vegetable productions.
As I at first observed, these islands are not so remarkable for the
number of the species of reptiles, as for that of the individuals,
when we remember the well-beaten paths made by the thousands of
huge tortoises - the many turtles - the great warrens of the
terrestrial Amblyrhynchus - and the groups of the marine species
basking on the coast-rocks of every island - we must admit that
there is no other quarter of the world where this Order replaces
the herbivorous mammalia in so extraordinary a manner. The
geologist on hearing this will probably refer back in his mind to
the Secondary epochs, when lizards, some herbivorous, some
carnivorous, and of dimensions comparable only with our existing
whales, swarmed on the land and in the sea. It is, therefore,
worthy of his observation that this archipelago, instead of
possessing a humid climate and rank vegetation, cannot be
considered otherwise than extremely arid, and, for an equatorial
region, remarkably temperate.

To finish with the zoology: the fifteen kinds of sea-fish which I
procured here are all new species; they belong to twelve genera,
all widely distributed, with the exception of Prionotus, of which
the four previously known species live on the eastern side of
America. Of land-shells I collected sixteen kinds (and two marked
varieties) of which, with the exception of one Helix found at
Tahiti, all are peculiar to this archipelago: a single fresh-water
shell (Paludina) is common to Tahiti and Van Diemen's Land. Mr.
Cuming, before our voyage, procured here ninety species of
sea-shells, and this does not include several species not yet
specifically examined, of Trochus, Turbo, Monodonta, and Nassa. He
has been kind enough to give me the following interesting results:
of the ninety shells, no less than forty-seven are unknown
elsewhere - a wonderful fact, considering how widely distributed
sea-shells generally are. Of the forty-three shells found in other
parts of the world, twenty-five inhabit the western coast of
America, and of these eight are distinguishable as varieties; the
remaining eighteen (including one variety) were found by Mr. Cuming
in the Low Archipelago, and some of them also at the Philippines.
This fact of shells from islands in the central parts of the
Pacific occurring here, deserves notice, for not one single
sea-shell is known to be common to the islands of that ocean and to
the west coast of America. The space of open sea running north and
south off the west coast separates two quite distinct conchological
provinces; but at the Galapagos Archipelago we have a
halting-place, where many new forms have been created, and whither
these two great conchological provinces have each sent several
colonists. The American province has also sent here representative
species; for there is a Galapageian species of Monoceros, a genus
only found on the west coast of America; and there are Galapageian
species of Fissurella and Cancellaria, genera common on the west
coast, but not found (as I am informed by Mr. Cuming) in the
central islands of the Pacific. On the other hand, there are
Galapageian species of Oniscia and Stylifer, genera common to the
West Indies and to the Chinese and Indian seas, but not found
either on the west coast of America or in the central Pacific. I
may here add, that after the comparison by Messrs. Cuming and Hinds
of about 2000 shells from the eastern and western coasts of
America, only one single shell was found in common, namely, the
Purpura patula, which inhabits the West Indies, the coast of
Panama, and the Galapagos. We have, therefore, in this quarter of
the world, three great conchological sea-provinces, quite distinct,
though surprisingly near each other, being separated by long north
and south spaces either of land or of open sea.

I took great pains in collecting the insects, but excepting Tierra
del Fuego, I never saw in this respect so poor a country. Even in
the upper and damp region I procured very few, excepting some
minute Diptera and Hymenoptera, mostly of common mundane forms. As
before remarked, the insects, for a tropical region, are of very
small size and dull colours. Of beetles I collected twenty-five
species (excluding a Dermestes and Corynetes imported wherever a
ship touches); of these, two belong to the Harpalidae, two to the
Hydrophilidae, nine to three families of the Heteromera, and the
remaining twelve to as many different families. This circumstance
of insects (and I may add plants), where few in number, belonging
to many different families, is, I believe, very general. Mr.
Waterhouse, who has published an account of the insects of this
archipelago, and to whom I am indebted for the above details,
informs me that there are several new genera; and that of the
genera not new, one or two are American, and the rest of mundane
distribution. (17/4. "Annals and Magazine of Natural History"
volume 16 page 19.) With the exception of a wood-feeding Apate, and
of one or probably two water-beetles from the American continent,
all the species appear to be new.

The botany of this group is fully as interesting as the zoology.
Dr. J. Hooker will soon publish in the "Linnean Transactions" a
full account of the Flora, and I am much indebted to him for the
following details. Of flowering plants there are, as far as at
present is known, 185 species, and 40 cryptogamic species, making
together 225; of this number I was fortunate enough to bring home
193. Of the flowering plants, 100 are new species, and are probably
confined to this archipelago. Dr. Hooker conceives that, of the
plants not so confined, at least 10 species found near the
cultivated ground at Charles Island have been imported. It is, I
think, surprising that more American species have not been
introduced naturally, considering that the distance is only between
500 and 600 miles from the continent, and that (according to
Collnet, page 58) drift-wood, bamboos, canes, and the nuts of a
palm, are often washed on the south-eastern shores. The proportion
of 100 flowering plants out of 185 (or 175 excluding the imported
weeds) being new, is sufficient, I conceive, to make the Galapagos
Archipelago a distinct botanical province; but this Flora is not
nearly so peculiar as that of St. Helena, nor, as I am informed by
Dr. Hooker, of Juan Fernandez. The peculiarity of the Galapageian
Flora is best shown in certain families; - thus there are 21 species
of Compositae, of which 20 are peculiar to this archipelago; these
belong to twelve genera, and of these genera no less than ten are
confined to the archipelago! Dr. Hooker informs me that the Flora
has an undoubted Western American character; nor can he detect in
it any affinity with that of the Pacific. If, therefore, we except
the eighteen marine, the one fresh-water, and one land-shell, which
have apparently come here as colonists from the central islands of
the Pacific, and likewise the one distinct Pacific species of the
Galapageian group of finches, we see that this archipelago, though
standing in the Pacific Ocean, is zoologically part of America.

If this character were owing merely to immigrants from America,
there would be little remarkable in it; but we see that a vast
majority of all the land animals, and that more than half of the
flowering plants, are aboriginal productions. It was most striking
to be surrounded by new birds, new reptiles, new shells, new
insects, new plants, and yet by innumerable trifling details of
structure, and even by the tones of voice and plumage of the birds,
to have the temperate plains of Patagonia, or the hot dry deserts
of Northern Chile, vividly brought before my eyes. Why, on these
small points of land, which within a late geological period must
have been covered by the ocean, which are formed of basaltic lava,
and therefore differ in geological character from the American
continent, and which are placed under a peculiar climate, - why were
their aboriginal inhabitants, associated, I may add, in different
proportions both in kind and number from those on the continent,
and therefore acting on each other in a different manner - why were
they created on American types of organisation? It is probable that
the islands of the Cape de Verd group resemble, in all their
physical conditions, far more closely the Galapagos Islands than
these latter physically resemble the coast of America, yet the
aboriginal inhabitants of the two groups are totally unlike; those
of the Cape de Verd Islands bearing the impress of Africa, as the
inhabitants of the Galapagos Archipelago are stamped with that of
America.

I have not as yet noticed by far the most remarkable feature in the
natural history of this archipelago; it is, that the different
islands to a considerable extent are inhabited by a different set
of beings. My attention was first called to this fact by the
Vice-Governor, Mr. Lawson, declaring that the tortoises differed
from the different islands, and that he could with certainty tell
from which island any one was brought. I did not for some time pay
sufficient attention to this statement, and I had already partially
mingled together the collections from two of the islands. I never
dreamed that islands, about 50 or 60 miles apart, and most of them
in sight of each other, formed of precisely the same rocks, placed
under a quite similar climate, rising to a nearly equal height,
would have been differently tenanted; but we shall soon see that
this is the case. It is the fate of most voyagers, no sooner to
discover what is most interesting in any locality, than they are
hurried from it; but I ought, perhaps, to be thankful that I
obtained sufficient materials to establish this most remarkable
fact in the distribution of organic beings.

The inhabitants, as I have said, state that they can distinguish
the tortoises from the different islands; and that they differ not
only in size, but in other characters. Captain Porter has described
those from Charles and from the nearest island to it, namely, Hood
Island, as having their shells in front thick and turned up like a
Spanish saddle, whilst the tortoises from James Island are rounder,
blacker, and have a better taste when cooked. (17/5. "Voyage in the
U.S. ship Essex" volume 1 page 215.) M. Bibron, moreover, informs
me that he has seen what he considers two distinct species of
tortoise from the Galapagos, but he does not know from which
islands. The specimens that I brought from three islands were young
ones: and probably owing to this cause neither Mr. Gray nor myself
could find in them any specific differences. I have remarked that
the marine Amblyrhynchus was larger at Albemarle Island than
elsewhere; and M. Bibron informs me that he has seen two distinct
aquatic species of this genus; so that the different islands
probably have their representative species or races of the
Amblyrhynchus, as well as of the tortoise. My attention was first
thoroughly aroused by comparing together the numerous specimens,
shot by myself and several other parties on board, of the
mocking-thrushes, when, to my astonishment, I discovered that all
those from Charles Island belonged to one species (Mimus
trifasciatus) all from Albemarle Island to M. parvulus; and all
from James and Chatham Islands (between which two other islands are
situated, as connecting links) belonged to M. melanotis. These two
latter species are closely allied, and would by some ornithologists
be considered as only well-marked races or varieties; but the Mimus
trifasciatus is very distinct. Unfortunately most of the specimens
of the finch tribe were mingled together; but I have strong reasons
to suspect that some of the species of the sub-group Geospiza are
confined to separate islands. If the different islands have their
representatives of Geospiza, it may help to explain the singularly
large number of the species of this sub-group in this one small
archipelago, and as a probable consequence of their numbers, the
perfectly graduated series in the size of their beaks. Two species
of the sub-group Cactornis, and two of the Camarhynchus, were
procured in the archipelago; and of the numerous specimens of these
two sub-groups shot by four collectors at James Island, all were
found to belong to one species of each; whereas the numerous
specimens shot either on Chatham or Charles Island (for the two
sets were mingled together) all belonged to the two other species:
hence we may feel almost sure that these islands possess their
representative species of these two sub-groups. In land-shells this
law of distribution does not appear to hold good. In my very small
collection of insects, Mr. Waterhouse remarks that of those which
were ticketed with their locality, not one was common to any two of
the islands.


TABLE 17/1.

Column 1 : Name of Island.

Column 2 : Total Number of species.

Column 3 : Number of species found in other parts of the world.

Column 4 : Number of Species confined to the Galapagos
Archipelago.

Column 5 : Number confined to the one island.

Column 6 : Number of Species confined to the Galapagos
Archipelago, but found on more than the one island.

James : 71 : 33 : 38 : 30 : 8.
Albemarle : 46 : 18 : 26 : 22 : 4.
Chatham : 32 : 16 : 16 : 12 : 4.
Charles : 68 : 39* : 29 : 21 : 8.
*(or 29, if the probably imported plants be
subtracted.)
If we now turn to the Flora, we shall find the aboriginal plants of
the different islands wonderfully different. I give all the
following results (Table 17/1) on the high authority of my friend
Dr. J. Hooker. I may premise that I indiscriminately collected
everything in flower on the different islands, and fortunately kept
my collections separate. Too much confidence, however, must not be
placed in the proportional results, as the small collections
brought home by some other naturalists though in some respects
confirming the results, plainly show that much remains to be done
in the botany of this group: the Leguminosae, moreover, have as yet
been only approximately worked out: -

Hence we have the truly wonderful fact, that in James Island, of
the thirty-eight Galapageian plants, or those found in no other
part of the world, thirty are exclusively confined to this one
island; and in Albemarle Island, of the twenty-six aboriginal
Galapageian plants, twenty-two are confined to this one island,
that is, only four are at present known to grow in the other
islands of the archipelago; and so on, as shown in the above table,
with the plants from Chatham and Charles Islands. This fact will,
perhaps, be rendered even more striking, by giving a few
illustrations: - thus, Scalesia, a remarkable arborescent genus of
the Compositae, is confined to the archipelago: it has six species:
one from Chatham, one from Albemarle, one from Charles Island, two
from James Island, and the sixth from one of the three latter
islands, but it is not known from which: not one of these six
species grows on any two islands. Again, Euphorbia, a mundane or
widely distributed genus, has here eight species, of which seven
are confined to the archipelago, and not one found on any two
islands: Acalypha and Borreria, both mundane genera, have
respectively six and seven species, none of which have the same
species on two islands, with the exception of one Borreria, which
does occur on two islands. The species of the Compositae are
particularly local; and Dr. Hooker has furnished me with several
other most striking illustrations of the difference of the species
on the different islands. He remarks that this law of distribution
holds good both with those genera confined to the archipelago, and
those distributed in other quarters of the world: in like manner we
have seen that the different islands have their proper species of
the mundane genus of tortoise, and of the widely distributed
American genus of the mocking-thrush, as well as of two of the
Galapageian sub-groups of finches, and almost certainly of the
Galapageian genus Amblyrhynchus.

The distribution of the tenants of this archipelago would not be
nearly so wonderful, if, for instance, one island had a
mocking-thrush, and a second island some other quite distinct
genus; - if one island had its genus of lizard, and a second island
another distinct genus, or none whatever; - or if the different
islands were inhabited, not by representative species of the same
genera of plants, but by totally different genera, as does to a
certain extent hold good; for, to give one instance, a large
berry-bearing tree at James Island has no representative species in
Charles Island. But it is the circumstance that several of the
islands possess their own species of the tortoise, mocking-thrush,
finches, and numerous plants, these species having the same general
habits, occupying analogous situations, and obviously filling the
same place in the natural economy of this archipelago, that strikes
me with wonder. It may be suspected that some of these
representative species, at least in the case of the tortoise and of
some of the birds, may hereafter prove to be only well-marked
races; but this would be of equally great interest to the
philosophical naturalist. I have said that most of the islands are
in sight of each other: I may specify that Charles Island is fifty
miles from the nearest part of Chatham Island, and thirty-three
miles from the nearest part of Albemarle Island. Chatham Island is
sixty miles from the nearest part of James Island, but there are
two intermediate islands between them which were not visited by me.
James Island is only ten miles from the nearest part of Albemarle
Island, but the two points where the collections were made are
thirty-two miles apart. I must repeat, that neither the nature of
the soil, nor height of the land, nor the climate, nor the general
character of the associated beings, and therefore their action one
on another, can differ much in the different islands. If there be
any sensible difference in their climates, it must be between the
windward group (namely, Charles and Chatham Islands), and that to
leeward; but there seems to be no corresponding difference in the
productions of these two halves of the archipelago.

The only light which I can throw on this remarkable difference in
the inhabitants of the different islands is that very strong
currents of the sea running in a westerly and west-north-westerly
direction must separate, as far as transportal by the sea is
concerned, the southern islands from the northern ones; and between
these northern islands a strong north-west current was observed,
which must effectually separate James and Albemarle Islands. As the
archipelago is free to a most remarkable degree from gales of wind,
neither the birds, insects, nor lighter seeds, would be blown from
island to island. And lastly, the profound depth of the ocean
between the islands, and their apparently recent (in a geological
sense) volcanic origin, render it highly unlikely that they were
ever united; and this, probably, is a far more important
consideration than any other with respect to the geographical
distribution of their inhabitants. Reviewing the facts here given,
one is astonished at the amount of creative force, if such an
expression may be used, displayed on these small, barren, and rocky
islands; and still more so, at its diverse yet analogous action on
points so near each other. I have said that the Galapagos
Archipelago might be called a satellite attached to America, but it
should rather be called a group of satellites, physically similar,
organically distinct, yet intimately related to each other, and all
related in a marked though much lesser degree, to the great
American continent.

I will conclude my description of the natural history of these
islands by giving an account of the extreme tameness of the birds.

This disposition is common to all the terrestrial species; namely,
to the mocking-thrushes, the finches, wrens, tyrant-flycatchers,
the dove, and carrion-buzzard. All of them often approached
sufficiently near to be killed with a switch, and sometimes, as I
myself tried, with a cap or hat. A gun is here almost superfluous;
for with the muzzle I pushed a hawk off the branch of a tree. One
day, whilst lying down, a mocking-thrush alighted on the edge of a
pitcher, made of the shell of a tortoise, which I held in my hand,
and began very quietly to sip the water; it allowed me to lift it
from the ground whilst seated on the vessel: I often tried, and
very nearly succeeded, in catching these birds by their legs.
Formerly the birds appear to have been even tamer than at present.
Cowley (in the year 1684) says that the "Turtledoves were so tame,
that they would often alight on our hats and arms, so as that we
could take them alive: they not fearing man, until such time as
some of our company did fire at them, whereby they were rendered
more shy." Dampier also, in the same year, says that a man in a
morning's walk might kill six or seven dozen of these doves. At
present, although certainly very tame, they do not alight on
people's arms, nor do they suffer themselves to be killed in such
large numbers. It is surprising that they have not become wilder;
for these islands during the last hundred and fifty years have been
frequently visited by bucaniers and whalers; and the sailors,
wandering through the wood in search of tortoises, always take
cruel delight in knocking down the little birds.

These birds, although now still more persecuted, do not readily
become wild: in Charles Island, which had then been colonised about
six years, I saw a boy sitting by a well with a switch in his hand,
with which he killed the doves and finches as they came to drink.
He had already procured a little heap of them for his dinner, and
he said that he had constantly been in the habit of waiting by this
well for the same purpose. It would appear that the birds of this
archipelago, not having as yet learnt that man is a more dangerous
animal than the tortoise or the Amblyrhynchus, disregard him, in
the same manner as in England shy birds, such as magpies, disregard
the cows and horses grazing in our fields.

The Falkland Islands offer a second instance of birds with a
similar disposition. The extraordinary tameness of the little
Opetiorhynchus has been remarked by Pernety, Lesson, and other
voyagers. It is not, however, peculiar to that bird: the Polyborus,
snipe, upland and lowland goose, thrush, bunting, and even some
true hawks, are all more or less tame. As the birds are so tame



Online LibraryCharles DarwinThe Voyage of the Beagle → online text (page 39 of 51)