Lamarck, the Founder of Evolution: His Life and Work

by A. S. Packard

“To sum up the results of our examination of certain series of fossil mammals, one sees clearly that transformation, whether in the way of the addition of new parts or the reduction of those already present, acts just as if the direct action of the environment and the habits of the animal were the efficient cause of the change, and any explanation which excludes the direct action of such agencies is confronted by the difficulty of an immense number of the most striking coincidences.... So far as I can see, the theory of determinate variations and of use-inheritance is not antagonistic but supplementary to natural selection, the latter theory attempting no explanation of the causes of variation. Nor is it pretended for a moment that use and disuse are the sole or even the chief factors in variation.”

As early as 1868 the Lamarckian factor of isolation, due to migration into new regions, was greatly extended, and shown by Moritz Wagner[234] to be a most important agent in the limitation and fixation of varieties and species.

“Darwin’s work,” he says, “neither satisfactorily explains the external cause which gives the first impulse to increased individual variability, and consequently to natural selection, nor that condition which, in connection with a certain advantage in the struggle for life, renders the new characteristics indispensable. The latter is, according to my conviction, solely fulfilled by the voluntary or passive migration of organisms and colonization, which depends in a great measure upon the configuration of the country; so that only under favorable conditions would the home of a new species be founded.”

This was succeeded by Rev. J. T. Gulick’s profound essays “On Diversity of Evolution under One Set of External Conditions”[235] (1872), and on “Divergent Evolution through Cumulative Segregation”[236] (1887).

These and later papers are based on his studies on the land shells of the Hawaiian Islands. The cause of their extreme diversity of local species is, he claims, not due to climatic conditions, food, enemies, or to natural selection, but to the action of what he calls the “law of segregation.”

Fifteen years later Mr. Romanes published his theory of physiological selection, which covered much the same ground.

A very strong little book by an ornithologist of wide experience, Charles Dixon,[237] and refreshing to read, since it is packed with facts, is Lamarckian throughout. The chief factor in the formation of local species is, he thinks, isolation; the others are climatic influences (especially the glacial period), use and disuse, and sexual selection as well as chemical agency. Dixon insists on the “vast importance of isolation in the modification of many forms of life, without the assistance of natural selection.” Again he says: “Natural selection, as has often been remarked, can only preserve a beneficial variation—it cannot originate it, it is not a cause of variation; on the other hand, the use or disuse of organs is a direct cause of variation, and can furnish natural selection with abundance of material to work upon” (p. 49). The book, like the papers of Allen, Ridgway, Gulick, and others, shows the value of isolation or segregation in special areas as a factor in the origination of varieties and species, the result being the prevention of interbreeding, which would otherwise swamp the incipient varieties.

Here might be cited Delbœuf’s law:[238]

“When a modification is produced in a very small number of individuals, this modification, even were it advantageous, would be destroyed by heredity, as the favored individuals would be obliged to unite with the unmodified individuals. Il n’en est rien, cependant. However great may be the number of forms similar to it, and however small may be the number of dissimilar individuals which would give rise to an isolated individual, we can always, while admitting that the different generations are propagated under the same conditions, meet with a number of generations at the end of which the sum total of the modified individuals will surpass that of the unmodified individuals.” Giard adds that this law is capable of mathematical demonstration. “Thus the continuity or even the periodicity of action of a primary factor, such, for example, as a variation of the milieu, shows us the necessary and sufficient condition under which a variety or species originates without the aid of any secondary factor.”

Semper,[239] an eminent zoölogist and morphologist, who also was the first (in 1863) to criticise Darwin’s theory of the mode of formation of coral atolls, though not referring to Lamarck, published a strong, catholic, and original book, which is in general essentially Lamarckian, while not undervaluing Darwin’s principle of natural selection. “It appears to me,” he says, in the preface, “that of all the properties of the animal organism, Variability is that which may first and most easily be traced by exact investigation to its efficient causes.”