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OriginOfSpecies - 475 Rows
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id int(11) 475 Column Stats
subject varchar(80) 14 Column Stats
title varchar(250) 139 Column Stats
ordinal int(11) 30 Column Stats
description text 474 Column Stats

475 rows, page 100 of 119 (4/p)
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12 - Geographical Distribution -- continued 12-50 - On colonisation from the nearest source with subsequent modification 90 I can hardly doubt that this rule is generally true, though it would be difficult to prove it.

Amongst mammals, we see it strikingly displayed in Bats, and in a lesser degree in the Felidae and Canidae.

bat
bat

cat
cat

dog
dog


We see it, if we compare the distribution of butterflies and beetles.

butterfly
butterfly

beetle
beetle
12 - Geographical Distribution -- continued 12-50 - On colonisation from the nearest source with subsequent modification 100 So it is with most fresh-water productions, in which so many genera range over the world, and many individual species have enormous ranges.

It is not meant that in world-ranging genera all the species have a wide range, or even that they have on an average a wide range; but only that some of the species range very widely; for the facility with which widely-ranging species vary and give rise to new forms will largely determine their average range.

For instance, two varieties of the same species inhabit America and Europe, and the species thus has an immense range; but, if the variation had been a little greater, the two varieties would have been ranked as distinct species, and the common range would have been greatly reduced.

Still less is it meant, that a species which apparently has the capacity of crossing barriers and ranging widely, as in the case of certain powerfully-winged birds, will necessarily range widely; for we should never forget that to range widely implies not only the power of crossing barriers, but the more important power of being victorious in distant lands in the struggle for life with foreign associates.

But on the view of all the species of a genus having descended from a single parent, though now distributed to the most remote points of the world, we ought to find, and I believe as a general rule we do find, that some at least of the species range very widely; for it is necessary that the unmodified parent should range widely, undergoing modification during its diffusion, and should place itself under diverse conditions favourable for the conversion of its offspring, firstly into new varieties and ultimately into new species.

In considering the wide distribution of certain genera, we should bear in mind that some are extremely ancient, and must have branched off from a common parent at a remote epoch; so that in such cases there will have been ample time for great climatal and geographical changes and for accidents of transport; and consequently for the migration of some of the species into all quarters of the world, where they may have become slightly modified in relation to their new conditions.

There is, also, some reason to believe from geological evidence that organisms low in the scale within each great class, generally change at a slower rate than the higher forms; and consequently the lower forms will have had a better chance of ranging widely and of still retaining the same specific character.

This fact, together with the seeds and eggs of many low forms being very minute and better fitted for distant transportation, probably accounts for a law which has long been observed, and which has lately been admirably discussed by Alph. de Candolle in regard to plants, namely, that the lower any group of organisms is, the more widely it is apt to range.

Alphonse de Candolle
Alphonse de Candolle


The relations just discussed, namely, low and slowly-changing organisms ranging more widely than the high, some of the species of widely-ranging genera themselves ranging widely, such facts, as alpine, lacustrine, and marsh productions being related (with the exceptions before specified) to those on the surrounding low lands and dry lands, though these stations are so different the very close relation of the distinct species which inhabit the islets of the same archipelago, and especially the striking relation of the inhabitants of each whole archipelago or island to those of the nearest mainland, are, I think, utterly inexplicable on the ordinary view of the independent creation of each species, but are explicable on the view of colonisation from the nearest and readiest source, together with the subsequent modification and better adaptation of the colonists to their new homes.
12 - Geographical Distribution -- continued 12-50 - On colonisation from the nearest source with subsequent modification 70 From these considerations I think we need not greatly marvel at the endemic and representative species, which inhabit the several islands of the Galapagos Archipelago, not having universally spread from island to island.

In many other instances, as in the several districts of the same continent, pre-occupation has probably played an important part in checking the commingling of species under the same conditions of life.

Thus, the south-east and south-west corners of Australia have nearly the same physical conditions, and are united by continuous land, yet they are inhabited by a vast number of distinct mammals, birds, and plants.

Australia
Australia


The principle which determines the general character of the fauna and flora of oceanic islands, namely, that the inhabitants, when not identically the same, yet are plainly related to the inhabitants of that region whence colonists could most readily have been derived, the colonists having been subsequently modified and better fitted to their new homes, is of the widest application throughout nature.

We see this on every mountain, in every lake and marsh.

For Alpine species, excepting in so far as the same forms, chiefly of plants, have spread widely throughout the world during the recent Glacial epoch, are related to those of the surrounding lowlands; thus we have in South America, Alpine humming-birds, Alpine rodents, Alpine plants, &c., all of strictly American forms, and it is obvious that a mountain, as it became slowly upheaved, would naturally be colonised from the surrounding lowlands.

Alps
Alps

South America
South America

Hummingbird
Hummingbird
12 - Geographical Distribution -- continued 12-60 - Summary of the last and present chapters 25 We can see why there should be some relation between the presence of mammals, in a more or less modified condition, and the depth of the sea between an island and the mainland.

We can clearly see why all the inhabitants of an archipelago, though specifically distinct on the several islets, should be closely related to each other, and likewise be related, but less closely, to those of the nearest continent or other source whence immigrants were probably derived.

We can see why in two areas, however distant from each other, there should be a correlation, in the presence of identical species, of varieties, of doubtful species, and of distinct but representative species.

As the late Edward Forbes often insisted, there is a striking parallelism in the laws of life throughout time and space: the laws governing the succession of forms in past times being nearly the same with those governing at the present time the differences in different areas.

Edward Forbes
Edward Forbes