Eimer's Orthogenesis





Organisation is due to internal causes. Structural characters crystallise

out, as it were. "Orthogenesis," or the definitely determined tendency of

evolution to advance in a few directions, is a law for the whole of the

animate world. In active response to the stimuli and influences of the

environment the organism expresses itself in "organic growth" without any

relation to utility. Butterflies in particular, and especially their

markings and coloration, are taken as illustrations. In the Darwinian

theory of "mimicry" these played a brilliant part. The great resemblance

to leaves, to dried twigs, or to well-protected species which are secure

from enemies, was regarded as the most convincing proof of the operation

of natural selection. But Eimer shows that markings, striping, spots, the

development of pattern, and the alleged or real resemblances to leaves,

are really subject to definite laws of growth, in obedience to which they

gradually appear, developing according to their own internal laws, varying

and progressing altogether by internal necessity, and without any

reference to advantage or disadvantage, In association with this

orthogenesis, Eimer recognises halmatogenesis, correlation and

"genepistasis" (coming to a standstill at a fixed and definite stage), and

these seem to him to make the Darwinian theory utterly impossible. The

text and the illustrations of the book show how, in the sequence of

evolution (according to Eimer's laws of transformation), the groupings of

stripes, bands, and eye-spots must have appeared on the butterfly's wing,

how convex or concave curvings of the contour must have come about at

certain points, so that the form of a "leaf" and the lines of its venation

resulted, how the eye-spots must have been moulded and shunted, so that

they produced the effect of rust or other spots on withered leaves.

Particular interest attaches to the detailed arguments against the idea

that the butterfly must receive some advantage from its "mimicry." Even

the Darwinians have to admit that in a whole series of cases the advantage

is not obvious. They talk with some embarrassment of "pseudomimicry." Some

butterflies that are supposed to be protected have the protective markings

on the underside, so that these are actually hidden when the insects are

flying from pursuing birds. Many of the leaf-like butterflies are not

wood-butterflies at all, but meadow species,(47) and so Eimer's arguments

continue.



A specially energetic fellow-worker on Eimer's line is W. Haacke, a

zoologist of Jena, author of "Gestaltung und Vererbung," and "Die

Schoepfung des Menschen und seiner Ideale."(48) In the first of these works

Haacke combats, energetically and with much detail, Weismann's

"preformation theory," and defends "epigenesis," for which he endeavours

to construct graphic diagrams, his aim being to make a foundation for the

inheritance of acquired characters, definitely directed evolution,

saltatory, symmetrical, and correlated variation.



The principles of the new school are very widespread to-day, but we cannot

here follow their development in the works of individual investigators,

such as Reinke, R. Hertwig, O. Hertwig, Wiesner, Hamann, Dreyer, Wolff,

Goette, Kassowitz, v. Wettstein, Korschinsky, and others.(49)





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