0000000000000797

AUTHOR

Charles Devillers

The history of life may be compared to a huge cable enclosing as many strands as there are fossil and present species. The biosphere, with its 2 million species, would then correspond to a transverse section through this cable.

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We have pointed out that the history of the giraffe’s neck served as an example to explain the theoretical concepts of transformism, proposed by J.-B. Lamarck, and of Darwin’s natural selection. However, at that time it had not been substantiated by palaeontological data. Since then, the record has furnished a number of fossils which enable us to reconstruct the major trends in the evolution of the giraffides of Africa, Asia, and Europe [1,2, 3] (Fig. 16.1; Appendix 16.1).

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This quote by J. Huxley reflects the present consensus between scientists, philosophers, and theologians alike, after a long period of fundamental disagreement on this crucial question for mankind.

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The formulation of the synthetic theory represented a significant-advance for evolutionary studies, which had previously been hampered by apparently irreconcilable contractions. Combining Mendelian laws with Darwinism, it joined the antitheses in a synthesis which was subsequently refined and completed. Today, its content may not be simply rejected or ignored, although there are those who think of it as little more than a corpse.

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We may state that the path of development of an organism can play an important role in its immediate realization and also in its possible transformation. This leads to the problem of the existence of a causative link between individual development (ontogeny) and evolutionary history (phylogeny). This problem which has been dealt with by numerous authors, has led to contradictory answers, depending on the direction of the supposed connection: from the evolutionary history to individual development or vice versa, that is, from individual development to the evolutionary history.

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This hotly debated question remains topical. Is biological evolution subjected to a strict determinism, to laws facilitating prediction, or is it at least in part subject to chance, and thereby unpredictable? We shall now consider this problem.

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Biology tells us about the processes and mechanisms which are able to explain effectively the changes occurring in organisms and species. Palaeontology, with the temporal dimension at its disposal, adds to this data which are indispensable for our understanding of speciation and of the patterns and rhythms of evolutionary change. Only through this we are able to observe the historical development of the evolution, of the living world as it took place through geological time. Based on data obtained from other branches of the earth sciences, palaeontology is able to evaluate the external constraints which frequently act at random on the living organism and which control the formation of new s…

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Let us sit on the terrace of a street cafe and watch the crowds pass by. The first basic unit we observe is the individual: tall, small, fat, long-faced, round-faced — the diversity is large. Among these individuals there will be a few with particular features, such as colour of skin or type of hair, which differ from the vast majority of local individuals, thereby indicating that they originated from another part of the world. We shall install a video camera at this site and will carry out the same observations simultaneously in Paris, Dakar, and Tokyo. When the films are then brought together and shown in the same room, the observers will not fail to note that the individuals of one city …

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Observers of the past and present noted an extraordinary diversity in the organic world: A snail is different from a river crayfish, which differs from a starfish, which in turn has nothing in common with a lobster or even man.

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From his studies on Invertebrate animals and fossils in the vicinity of Paris, J.-B. de Lamarck (1744–1829) formulated a number of conclusions in his Zoological Philosophy [1] (1809), the first coherent theory of evolution. However, in contrast to commonly held belief, this was not based purely on speculation, but was progressively elaborated.

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The key stages in the history of the living world may be summed up as follows: formation of the major types of body plan at the start of the Cambrian, with the appearance of the last, the vertebrates, during the upper Cambrian. Thereafter evolution took place within these plans through “modulations” exploiting a number of possibilities.

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One of the first difficulties encountered when trying to understand evolution is the concept of geological time, for which we have no comparison in everyday life.

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Extending the species concept in time leads us to understand evolution as a dynamic process which takes place at different rates and in different patterns. We shall examine this below.

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Genetics and developmental genetics have given us such a wealth of new insight that, at the end of this century, the synthetic theory can no longer be maintained in the strict “orthodox” sense in which it was started.

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The genetic material containts the instructions necessary for the construction of an organism and ensures the continuity of the species by transmission of the construction plan from generation to generation over considerable periods of time.

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Jean-Baptiste de Lamarck [1], who introduced the concept of transformism, interpreted the lengthening of the giraffe neck by the animal’s desire to reach the higher leaves in trees: “As far as habits are concerned, it is of interest to observe its result, the particular shape of the giraffe (G. camelopardalis) and its size. We know that this tallest of all mammals lives in the African interior in areas which are almost continuously dry and without a grass cover. The animal thus has to live off the foliage of trees and has to strain itself continously to reach this foliage. As a result of this sustained habit, eventually in all individuals of this race, the front legs become longer than the …

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Lobsters and dolphins are adapted to aquatic life whereas the green woodpecker and the fly are adapted to aerial life. The way in which these organisms are constructed allows them to execute certain functions within certain environments. This is a first, simple definition of adaptation which describes:The evolutionary process of adjustment of an organism to its environment. This historical aspect will be discussed in subsequent chapters.The result of this process — the state of adaptation — or the form of an organism at a certain point in its history. This functional-structural aspect will be dealt with here.

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