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Author Topic:   Alfred Russel Wallace and Biogeography
RAZD
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Message 1 of 8 (721559)
03-09-2014 11:58 AM


The Law of Sarawak
On the Law Which Has Regulated the Introduction of New Species

quote:
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: http://people.wku.edu/charles.smith/wallace/S020.htm

This is the paper where Wallace first published his "Sarawak Law" that he developed from his pursuit of biogeographical and geological relationships:

quote:
The following propositions in Organic Geography and Geology give the main facts on which the hypothesis is founded.

Geography.

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.

Geology.

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 phænomena of representative groups, and those which Professor Forbes supposed to manifest polarity. 4th. The phænomena 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:

quote:
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, and "affinity" is used where today we would use homology.

This is 3 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.

Edited by RAZD, : .

Edited by RAZD, : 3 not 10

Edited by RAZD, : format, subtitle


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Message 2 of 8 (721561)
03-09-2014 2:42 PM


Thread Copied from Proposed New Topics Forum
Thread copied here from the Alfred Russel Wallace and Biogeography thread in the Proposed New Topics forum.
  
RAZD
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Message 3 of 8 (721643)
03-10-2014 5:45 PM
Reply to: Message 1 by RAZD
03-09-2014 11:58 AM


The Malthus Connection
Sadly I have not yet found a copy of the entire letter concerning his epiphany regarding Malthus, just excerpts from it:

The Letter from Wallace to Darwin ...

quote:
Wallace had been away since 1854, on his expedition to the Malay Archipelago. Years later, in his autobiography, he wrote how the theory came to him, in February 1858, in his bungalow on the remote island of Ternate (pronounced "turn-NAW-tay"). "At the time in question I was suffering from a sharp attack of intermittent [malarial] fever, and every day during the cold and succeeding hot fits had to lie down for several hours, during which time I had nothing to do but to think over any subjects then particularly interesting me. One day,
something brought to my recollection Malthus's "Principles of Population" … I thought of his clear exposition of "the positive checks to increase"—disease, accidents, war, and famine—which keep down the population … It then occurred to me that these causes or their equivalents are continually acting in the case of animals also; and as animals usually breed much more rapidly than does mankind, the destruction every year from these causes must be enormous in order to keep down the numbers of each species, since they evidently do not increase regularly from year to year, as otherwise the world would long ago have been densely crowded with those that breed most quickly. [Then] it occurred to me to ask the question, Why do some die and some live? And the answer was clearly, that on the whole the best fitted live. … that is, the fittest would survive. … The more I thought over it the more I became convinced that I had at length found the long-sought-for law of nature that solved the problem of the origin of species. … on the two succeeding evenings I wrote [the theory] out carefully in order to send it to Darwin by the next post. [Alfred Russel Wallace, My Life, pp. 361-363]

What I could find is the manuscript that he sent and that was read together with some material from Darwin

On the Tendency of Varieties to Depart Indefinitely From the Original Type

quote:
Editor Charles H. Smith's Note: This is the famous "Ternate essay" introducing natural selection that Wallace sent to Charles Darwin in February of 1858. This paper, along with excerpts from two unpublished writings by Darwin, was read before a special meeting of the Linnean Society of London on 1 July 1858, and published on pages 53-62 of Volume 3 of that Society's Proceedings series. It should thus be noted that, frequently seen comments to the contrary notwithstanding, Wallace did not "publish a paper describing natural selection before Darwin did"--in fact, there is conclusive historical evidence1 that even Wallace's own paper had not been intended for publication in the form in which it was sent to Darwin. Original pagination indicated within double brackets. To link directly to this page, connect with: http://people.wku.edu/charles.smith/wallace/S043.htm

... Even the least prolific of animals would increase rapidly if unchecked, whereas it is evident that the animal population of the globe must be stationary, or perhaps, through the influence of man, decreasing. Fluctuations there may be; but permanent increase, except in restricted localities, is almost impossible. For example, our own observation must convince us that birds do not go on increasing every year in a geometrical ratio, as they would do, were there not [[p. 55] some powerful check to their natural increase. Very few birds produce less than two young ones each year, while many have six, eight, or ten; four will certainly be below the average; and if we suppose that each pair produce young only four times in their life, that will also be below the average, supposing them not to die either by violence or want of food. Yet at this rate how tremendous would be the increase in a few years from a single pair! A simple calculation will show that in fifteen years each pair of birds would have increased to nearly ten millions! ... It appears evident, therefore, that so long as a country remains physically unchanged, the numbers of its animal population cannot materially increase. If one species does so, some others requiring the same kind of food must diminish in proportion. The numbers that die annually must be immense; and as the individual existence of each animal depends upon itself, those that die must be the weakest--the very young, the aged, and the diseased,--while those that prolong their existence can only be the most perfect in health and vigour--those who are best able to obtain food regularly, and avoid their numerous enemies. It is, as we commenced by remarking, "a struggle for existence," in [[p. 57] which the weakest and least perfectly organized must always succumb.


That lays out the Malthusian argument regarding natural selection and the struggle for survival. But there is more (as promised in the title):

quote:
Now it is clear that what takes place among the individuals of a species must also occur among the several allied species of a group,--viz. that those which are best adapted to obtain a regular supply of food, and to defend themselves against the attacks of their enemies and the vicissitudes of the seasons, must necessarily obtain and preserve a superiority in population; while those species which from some defect of power or organization are the least capable of counteracting the vicissitudes of food, supply, &c., must diminish in numbers, and, in extreme cases, become altogether extinct. Between these extremes the species will present various degrees of capacity for ensuring the means of preserving life; and it is thus we account for the abundance or rarity of species. ...

Most or perhaps all the variations from the typical form of a species must have some definite effect, however slight, on the habits or capacities of the individuals. Even a change of colour might, by rendering them more or less distinguishable, affect their safety; a greater or less development of hair might modify their habits. More important changes, such as an increase in the power or dimensions of the limbs or any of the external organs, would more or less affect their mode of procuring food or the range of [[p. 58] country which they inhabit. ... Now, let some alteration of physical conditions occur in the district--a long period of drought, a destruction of vegetation by locusts, the irruption of some new carnivorous animal seeking "pastures new"--any change in fact tending to render existence more difficult to the species in question, and tasking its utmost powers to avoid complete extermination; it is evident that, of all the individuals composing the species, those forming the least numerous and most feebly organized variety would suffer first, and, were the pressure severe, must soon become extinct. The same causes continuing in action, the parent species would next suffer, would gradually diminish in numbers, and with a recurrence of similar unfavourable conditions might also become extinct. The superior variety would then alone remain, and on a return to favourable circumstances would rapidly increase in numbers and occupy the place of the extinct species and variety.

The variety would now have replaced the species, of which it would be a more perfectly developed and more highly organized form. It would be in all respects better adapted to secure its safety, and to prolong its individual existence and that of the race. Such a variety could not return to the original form; for that form is an inferior one, and could never compete with it for existence.


And there you have the development of new species by the process of natural selection. He then contrasts this process with the Lamarkian view of acquired traits:

quote:
The hypothesis of Lamarck--that progressive changes in species have been produced by the attempts of animals to increase the development of their own organs, and thus modify their structure and habits--has been repeatedly and easily refuted by all writers on the subject of varieties and species, and it seems to have been considered that when this was done the whole question has been finally settled; but the view here developed renders such an hypothesis quite unnecessary, by showing that similar results must be produced by the action of principles constantly at work in nature. The powerful retractile talons of the falcon- and the cat-tribes have not been produced or increased by the volition of those animals; but among the different varieties which occurred in the earlier and less highly organized forms of these groups, those always survived longest which had the greatest facilities for seizing their prey. Neither did the giraffe acquire its long neck by desiring to reach the foliage of the more lofty shrubs, and constantly stretching its neck for the purpose, but because any varieties which occurred among its antitypes with a longer neck than usual at once secured a fresh range of pasture over the same ground as their shorter-necked companions, and on the first scarcity of food were thereby enabled to outlive them ...

And he ends with a summary statement:

quote:
We believe we have now shown that there is a tendency in nature to the continued progression of certain classes of varieties further and further from the original type--a progression to which there appears no reason to assign any definite limits--and that the same principle which produces this result in a state of nature will also explain why domestic varieties have a tendency to revert to the original type. This progression, by minute steps, in various directions, but always checked and balanced by the necessary conditions, subject to which alone existence can be preserved, may, it is believed, be followed out so as to agree with all the phenomena presented by organized beings, their extinction and succession in past ages, and all the extraordinary modifications of form, instinct, and habits which they exhibit.

Thus evolution is an ongoing process.

But Wallace is not done, for he has another direction to go.

Edited by RAZD, : format


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RAZD
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Message 4 of 8 (721848)
03-12-2014 2:25 PM
Reply to: Message 3 by RAZD
03-10-2014 5:45 PM


Beyond Natural Selection
Having realized\discovered the process whereby new species develop via natural selection from varieties existing within breeding populations, Wallace looks to geographic distributions of fossils and living animals to show how geography has and is affecting this process:

On the Zoological Geography of the Malay Archipelago

quote:
Editor Charles H. Smith's Note: In this paper, presented to the Linnean Society on 3 November 1859 (and published in their Zoological Proceedings the next year), Wallace describes in detail for the first time the faunal discontinuity that would later bear his name: "Wallace's Line." Original pagination indicated within double brackets. To link directly to this page, connect with: http://people.wku.edu/charles.smith/wallace/S053.htm

The Australian and Indian regions of Zoology are very strongly contrasted. In one the Marsupial order constitutes the great mass of the mammalia,--in the other not a solitary marsupial animal exists. Marsupials of at least two genera (Cuscus and Belideus) are found all over the Moluccas and in Celebes; but none have [[p. 173] been detected in the adjacent islands of Java and Borneo. Of all the varied forms of Quadrumana, Carnivora, Insectivora, and Ruminantia which abound in the western half of the Archipelago, the only genera found in the Moluccas are Paradoxurus and Cervus. The Sciuridæ, so numerous in the western islands, are represented in Celebes by only two or three species, while not one is found further east. Birds furnish equally remarkable illustrations. The Australian region is the richest in the world in Parrots; the Asiatic is (of tropical regions) the poorest. Three entire families of the Psittacine order are peculiar to the former region, and two of them, the Cockatoos and the Lories, extend up to its extreme limits, without a solitary species passing into the Indian islands of the Archipelago. The genus Palæornis is, on the other hand, confined with equal strictness to the Indian region. In the Rasorial order, the Phasianidæ are Indian, the Megapodiidæ Australian; but in this case one species of each family just passes the limits into the adjacent region. The genus Tropidorhynchus, highly characteristic of the Australian region, and everywhere abundant as well in the Moluccas and New Guinea as in Australia, is quite unknown in Java and Borneo. On the other hand, the entire families of Bucconidæ, Trogonidæ and Phyllornithidæ, and the genera Pericrocotus, Picnonotus, Trichophorus, Ixos, in fact, almost all the vast family of Thrushes and a host of other genera, cease abruptly at the eastern side of Borneo, Java, and Bali. All these groups are common birds in the great Indian islands; they abound everywhere; they are the characteristic features of the ornithology; and it is most striking to a naturalist, on passing the narrow straits of Macassar and Lombock, suddenly to miss them entirely, together with the Quadrumana and Felidæ, the Insectivora and Rodentia, whose varied species people the forests of Sumatra, Java, and Borneo.

To define exactly the limits of the two regions where they are (geographically) most intimately connected, I may mention that during a few days' stay in the island of Bali I found birds of the genera Copsychus, Megalaima, Tiga, Ploceus, and Sturnopastor, all characteristic of the Indian region and abundant in Malacca, Java, and Borneo; while on crossing over to Lombock, during three months collecting there, not one of them was ever seen; neither have they occurred in Celebes nor in any of the more eastern islands I have visited. Taking this in connexion with the fact of Cacatua, Tropidorhynchus, and Megapodius having their western limit in Lombock, we may consider it established that the Strait of Lombock [[p. 174] (only 15 miles wide) marks the limits and abruptly separates two of the great Zoological regions of the globe. ...

Moreover there is nothing in the aspect or physical character of the islands to lead us to expect such a difference; their physical and geological differences do not coincide with the zoological differences. There is a striking homogeneity in the two halves of the Archipelago. The great volcanic chain runs through both parts; Borneo is the counterpart of New Guinea; the Philippines closely resemble the equally fertile and equally volcanic Moluccas; while in eastern Java begins to be felt the more arid climate of Timor and Australia. But these resemblances are accompanied by an extreme zoological diversity, the Asiatic and Australian regions finding in Borneo and New Guinea respectively their highest development.

In the brief sketch I have now given of this interesting subject, such obvious and striking facts alone have been adduced as a traveller's note-book can supply. The argument must therefore lose much of its weight from the absence of detail and accumulated examples. There is, however, such a very general accordance in the phenomena of distribution as separately deduced from the various classes or kingdoms of the organic world, that whenever one class of animals or plants exhibits in a clearly marked manner certain relations between two countries, the other classes will certainly show similar ones, though it may be in a greater or a less degree. ...


Wallace describes in great detail the divisions of species between the Malaysian types that predominate on the Malaysian islands and mainland, and the Australian types that predominate on the Australian islands and continent, geographical areas connected by their respective continental shelf.

He posits how the islands were colonized when these continental shelves were above sea level, and then their flora and fauna become isolated as the seas rose.

He ties the geographical distribution to the geological history.


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RAZD
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From: the other end of the sidewalk
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Message 5 of 8 (721857)
03-12-2014 6:12 PM
Reply to: Message 4 by RAZD
03-12-2014 2:25 PM


Wallace draws a line
In the previous post Wallace discussed the division of species between Malaysia and Australia and tied it into ancient (prehistorical) gelogical distributions and this theme is then further developed in another paper:

On the Physical Geography of the Malay Archipelago

quote:
Editor Charles H. Smith's Note: This paper, read at the Royal Geographical Society meeting of 8 June 1863 (and published in volume 33 of their Journal series later the same year), was a notable success, and did much to solidify Wallace's reputation as the leading expert on the natural history of the Indonesia region. Discussion following the paper's presentation was recorded, separately, in volume seven (for 1862-63), issue five, of the Society's Proceedings series. Both are reproduced below, with the original paginations indicated within double brackets. To link directly to this page, connect with: http://people.wku.edu/charles.smith/wallace/S078.htm

The Malay or Indian Archipelago is that extensive group of islands which occupies the space between south-eastern Asia and Australia, and divides the Indian from the Pacific Ocean. ...

In their physical constitution and attendant phenomena the islands of the Archipelago offer us some remarkable and instructive contrasts. Active and extinct volcanoes are abundant in many of the islands, in others they are altogether absent. The former, as a general rule, are subject to frequent earthquakes, which in the others are quite unknown. In the greater part of the Archipelago one vast, ever-verdant forest covers hill and valley, plain and mountain, up to the very loftiest summits; whereas in another and much smaller portion such dense and gloomy forests are altogether unknown, the country consisting of arid hills and plains, with a comparatively scanty covering of shrubs and trees. Again, over some extensive districts the monsoons, or periodical winds, with their attendant rains or drought, divide the year into a well-defined and regularly-recurring wet and dry season. Over other scarcely less extensive districts no such regularity exists; the inhabitants themselves can hardly tell you when their rainy or dry season usually begins, and the traveller soon finds the climate to be almost as variable and the skies as inconstant as in our own much-abused island. Even in districts where the season is regular, there are no less striking contrasts; one portion of an island having its wet weather while the remainder is parched up, and islands within sight of each other having very different seasons.

There is yet another contrasting aspect in which the Archipelago may be viewed, less obvious but leading to far more important results than any I have yet mentioned, namely, that one large portion of it is connected by a very shallow sea to the continent of Asia, another part is similarly joined to Australia, while the remaining islands are surrounded by a practically unfathomable ocean. We shall consider the chief islands of the Archipelago, therefore, under the heads of,--1st. Volcanic and Non-Volcanic; 2nd. Forest Country and Open Country; 3rd. Well-marked Seasons and Undefined Seasons; and 4th. The Western or Indo-Malayan Region, and the Eastern or Austro-Malayan Region.

The contrasts of vegetation and of climate in the Archipelago may best be considered together, the one being to some extent dependent on the other.

Placed immediately upon the Equator, and surrounded by extensive oceans, it is not surprising that the various islands of the Archipelago should be almost always clothed with a forest vegetation from the level of the sea to the summits of the loftiest mountains. This is the general rule. Sumatra, New Guinea, Borneo, the Philippines and the Moluccas, and the uncultivated parts of Java and Celebes, are all forest countries, except a few small and unimportant tracts, due perhaps, in some cases, to ancient cultivation or accidental fires. To this, however, there is one important exception in the island of Timor and all the smaller islands opposite, in which there is absolutely no forest such as exists in the other islands, and this character extends in a lesser degree to Flores, Sumbawa, Lombock, and Bali.

In Timor the most common trees are Eucalypti of several species, so characteristic of Australia, with sandalwood, acacia, and other sorts in less abundance. These are scattered over the country more or less thickly, but never so as to deserve the name of a forest. Coarse and scanty grasses grow beneath them on the more barren hills, and a luxuriant herbage in the moister localities. ... This peculiar character, which extends in a less degree to the southern peninsula of Celebes and the east end of Java, is most probably owing to the proximity of Australia. ...

It was first pointed out by Mr. George Windsor Earl, in a paper read before this Society eighteen years ago, that a shallow sea connected the great islands of Sumatra, Borneo, and Java, to the Asiatic continent, with which they generally agreed in their natural productions; while a similar shallow sea connected New Guinea and some of the adjacent islands to Australia. ...

In order to make this subject intelligible, it is necessary to make a few observations on the relations of the geographical distribution of animals and plants with geology.

Now, in all cases where we have independent geological evidence, we find that those islands, the productions of which are identical with those of the adjacent countries, have been joined to them within a comparatively recent period, such recent unity being in most cases indicated by the very shallow sea still dividing them; while in cases where the natural productions of two adjacent countries is very different, they have been separated at a more remote epoch--a fact generally indicated by a deeper sea now dividing them. ...

The nature of the contrast between these two great divisions of the Malay Archipelago will be best understood by considering what would take place if any two of the primary divisions of the earth were brought into equally close contact. Africa and South America, for example, differ very greatly in all their animal forms. On the one side we have baboons, lions, elephants, buffaloes, and giraffes; on the other spider-monkeys, pumas, tapirs, ant-eaters, and sloths; while among birds, the hornbills, turacos, orioles, and honey-suckers of Africa contrast strongly with the toucans, macaws, chatterers, and humming-birds of America.


By evaluating the differences in geology, fauna, flora and fossils in this area, Wallace anticipates plate tectonics, where we now know that the Australian plate is in collision with the Indo-Malaysian plate, with the subduction causing the volcanoes and earthquakes,

Wallace draws his famous line (see map above) where the Malaysian portion is well defined by the species that occupy the islands (later biologists draw a second line closer to Australia and call the area in between Wallacea), and this is the zone of subuction.

There is a massive consilience between the biological data, paleontological data, and the geological data showing that Australian plate and biology were once connected\linked to South America and have only recently (in geological terms) come into contact with the Indo-Malaysian plate and biology.


we are limited in our ability to understand
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This message is a reply to:
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RAZD
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Message 6 of 8 (722136)
03-16-2014 10:30 PM
Reply to: Message 5 by RAZD
03-12-2014 6:12 PM


Missing Informations and Anticipating Ecology
Just as Darwin's work on the evolution of new traits suffered from a lack of information about genetic inheritance, even while such knowledge was (at least in rudimentary form) available from Mendel's work on pea plants, so too did Wallace's work on biogeography suffer from a lack of information on two aspects that could have made his arguments even more persuasive.

I am currently reading Wallace's book

The Geographic Distribution of Animals
With a Study of the Relations of Living and Extinct Faunas
as Elucidating the Past Changes of the Earth's Surface.

(The book has been scanned by a rather poor program that leaves many amusing or confusing typos (Humble Bees for instance).h

The first piece of missing information I have already alluded to: plate tectonics, knowledge of which would have made his tracing of the history of "affinities" into the past, the ancestors of modern species, without having to posit the rise and fall of whole continents in and out of the seas. Such rising and falling, while explaining much of what is seen on islands on continental shelfs, does not explain the "affinities" between South America and Australia without a massive continental piece that came and went.

The second is bacteria, and here the parallel to Darwin's missing genetic inheritance information is even closer, for Louis Pasteur was showing the link between diseases and bacteria at about the same time as Wallace was writing this book.

quote:
Beverage contamination led Pasteur to the idea that micro-organisms infecting animals and humans cause disease. He proposed preventing the entry of micro-organisms into the human body, leading Joseph Lister to develop antiseptic methods in surgery.

In 1865, two parasitic diseases called pébrine and flacherie were killing great numbers of silkworms at Alais (now Alès). Pasteur worked several years proving that these diseases were caused by a microbe attacking silkworm eggs, and that eliminating the microbe in silkworm nurseries would eradicate the disease.[14]


And Wallace has this paragraph in his book:

quote:
Organic Changesas affccting Distribution. -- We have now briefly touched on some of the direct effects of changes in physical geography, climate, and vegetation, on the distribution of animals; but the indirect effects of such changes are probably of quite equal, if not of greater importance. Every change becomes the centre of an ever-widening circle of effects. The different members of the organic world are so bound together by complex relations, that any one change generally involves numerous other changes, often of the most unexpected kind. We know comparatively little of the way in which one animal or plant is bound up with others, but we know enough to assure us that groups the most apparently disconnected are often dependent on each other. We know, for example, that the introduction of goats into St. Helena utterly destroyed a whole flora of forest trees; and with them all the insects, mollusca, and perhaps birds directly or indirectly dependent on them. Swine, which ran wild in Mauritius, exterminated the Dodo. The same animals are known to be the greatest enemies of venomous serpents. Cattle will, in many districts, wholly prevent the growth of trees; and with the trees the numerous insects dependent on those trees, and the birds which fed upon the insects, must disappear, as well as the small mammalia which feed on the fruits, seeds, leaves, or roots. Insects again have the most wonderful influence on the range of mammalia. In Paraguay a certain species of fly abounds which destroys new-born cattle and horses; and thus neither of these animals have run wild in that country, although they abound both north and south of it. This inevitably leads to a great difference in the vegetation of Paraguay, and through that to a difference in its insects, birds, reptiles, and wild mammalia. On what causes the existence of the fly depends we do not know, but it is not improbable that some comparatively slight changes in the temperature or humidity of the air at a particular season, or the introduction of some enemy might lead to its extinction or banishment. The whole face of the country would then soon be changed: new species would come in, while many others would be unable to live there; and the immediate cause of this great alteration would probably be quite imperceptible to us, even if we could watch it in progress year by year. So, in South Africa, the celebrated Tsetse fly inhabits certain districts having well defined limits; and where it abounds no horses, dogs, or cattle can live. Yet asses, zebras, and antelopes are unaffected by it. So long as this fly continues to exist, there is a living barrier to the entrance of certain animals, quite as effectual as a lofty mountain range or a wide arm of the sea. The complex relations of one form of life with others is nowhere better illustrated than in Mr. Darwin's celebrated case of the cats and clover, as given in his Origin of Species, 6th ed., p. 57. He has observed that both wild heartsease and red-clover are fertilized in this country by bumble-bees only, so that the production of seed depends on the visits of these insects. A gentleman who has specially studied bumble-bees finds that they are largely kept down by field-mice, which destroy their combs and nests. Field-mice in their turn are kept down by cats; and probably also by owls; so that these carnivorous animals are really the agents in rendering possible the continued existence of red-clover and wild heartsease. For if they were absent, the field-mice having no enemies, would multiply to such an extent as to destroy all the bumble-bees; and these two plants would then produce no seed and soon become extinct.

Note that I have corrected some of the scanning typos, and I have bolded the pertinent parts for this second point: most likely it is not the insects but bacteria that they carry that are responsible for these effects, and knowledge of Pasteur's work would have shed light on this.

What Wallace writes here anticipates ecology and the study of the web of life in each ecological domain.


Edited by RAZD, : .

Edited by RAZD, : ..


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This message is a reply to:
 Message 5 by RAZD, posted 03-12-2014 6:12 PM RAZD has acknowledged this reply

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Pollux
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Posts: 201
Joined: 11-13-2011


(1)
Message 7 of 8 (722192)
03-17-2014 10:53 PM
Reply to: Message 6 by RAZD
03-16-2014 10:30 PM


The humble bumble-bee
Hi RAZD
"Humble" is not a typo but the usual name for the bee at his time of writing, though bumble was also sometimes used. Bumble really took over from early 20th century.
Thanks for your -as usual- interesting posts!
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RAZD
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Posts: 19295
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.3


Message 8 of 8 (722574)
03-22-2014 6:24 PM
Reply to: Message 7 by Pollux
03-17-2014 10:53 PM


Re: The humble bumble-bee
The PDF download is much better for reading, but not for copying text. The PDF does say "humble-bee" so I do stand corrected, thank you.
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