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Author Topic:   Alfred Russel Wallace and Biogeography
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Message 1 of 2 (721545)
03-09-2014 11:58 AM

On the Law Which Has Regulated the Introduction of New Species
Editor Charles H. Smith's Note: This paper, written at Sarawak in Borneo in February of 1855 and published in Volume 16 (2nd Series) of the Annals and Magazine of Natural History in September 1855, conveys Wallace's first formal statement of his understanding--a pre-natural selection understanding--of the process of biological evolution. Original pagination indicated within double brackets. To link directly to this page, connect with: On the Law Which Has Regulated the Introduction of New Species, by Alfred Russel Wallace
This is the paper where Wallace first published his "Sarawak Law" that he developed from his pursuit of biogeographical and geological relationships:
The following propositions in Organic Geography and Geology give the main facts on which the hypothesis is founded.
1. Large groups, such as classes and orders, are generally spread over the whole earth, while smaller ones, such as families and genera, are frequently confined to one portion, often to a very limited district.
2. In widely distributed families the genera are often limited in range; in widely distributed genera, well-marked groups of species are peculiar to each geographical district.
3. When a group is confined to one district, and is rich in species, it is almost invariably the case that the most closely allied species are found in the same locality or in closely adjoining localities, and that therefore the natural sequence of the species by affinity is also geographical.
4. In countries of a similar climate, but separated by a wide sea or lofty mountains, the families, genera and species of the [[p. 186] one are often represented by closely allied families, genera and species peculiar to the other.
5. The distribution of the organic world in time is very similar to its present distribution in space.
6. Most of the larger and some small groups extend through several geological periods.
7. In each period, however, there are peculiar groups, found nowhere else, and extending through one or several formations.
8. Species of one genus, or genera of one family occurring in the same geological time are more closely allied than those separated in time.
9. As generally in geography no species or genus occurs in two very distant localities without being also found in intermediate places, so in geology the life of a species or genus has not been interrupted. In other words, no group or species has come into existence twice.
10. The following law may be deduced from these facts:--Every species has come into existence coincident both in space and time with a pre-existing closely allied species.
This law agrees with, explains and illustrates all the facts connected with the following branches of the subject:--1st. The system of natural affinities. 2nd. The distribution of animals and plants in space. 3rd. The same in time, including all the phnomena of representative groups, and those which Professor Forbes supposed to manifest polarity. 4th. The phnomena of rudimentary organs. We will briefly endeavour to show its bearing upon each of these.
color and bold added: this is known as "The Law of Sarawak" and this formulation is an important step in his development of a theory of evolution.
He goes on to discusses how this law results in nested hierarchies of relationships between living and extinct groups:
If the law above enunciated be true, it follows that the natural series of affinities will also represent the order in which the several species came into existence, each one having had for its immediate antitype a closely allied species existing at the time of its origin. It is evidently possible that two or three distinct species may have had a common antitype, and that each of these may again have become the antitypes from which other closely allied species were created. The effect of this would be, that so long as each species has had but one new species formed on its model, the line of affinities will be simple, and may be represented by placing the several species in direct succession in a straight line. But if two or more species have been independently formed on the plan of a common antitype, then the series of affinities will be compound, and can only be represented by a forked or many-branched line. ....
Here "antitype" (antetype) is used where today we would use "common ancestor" for the ancestral population.
This is 10 years before he (or Darwin) ties the population dynamics of Malthus together with natural selection, but it shows that he had developed the basis for the theory of evolution.
This also shows the basis for biogeography that is his legacy.

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Message 2 of 2 (721560)
03-09-2014 2:42 PM

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