Tiedemann, 2 the Heidelberg anatomist, who has been generally ignored, although he surpassed many a recent zoogeographer by the wide view he took of the problem; in fact he was the first to connect distribution with environmental or bionomic factors; e.g.
If a character of much longer standing (certain properties of height, length, breadth, colour, &c.) had not become fixed and congenital after many thousands of successive generations of individuals had developed it in response to environment, but gave place to a new character when new moulding conditions operated on an individual (Lamarck's first law), why should we suppose that the new character is likely to become fixed and transmitted by mere heredity after a much shorter time of existence in response to environmental stimulus ?
Beginning in 1793 he boldly advocated evolution, and further elaborated five great principles--namely, the method of comparison of extinct and existing forms, the broad sequence of formations and succession of epochs, the correlation of geological horizons by means of fossils, the climatic or environmental changes as influencing the development of species, the inheritance of the bodily modifications caused by change of habit and habitat.
- In the long vicissitudes of time and procession of continental changes, animals have been subjected to alternations of habitat either through their own migrations or through the " migration of the environment itself," to employ Van den Broeck's epigrammatic description of the profound and sometimes sudden environmental changes which may take place in a single locality.
This is not due to environmental conditions solely, because senescent branches of normal progressive groups are found in all geologic horizons, beginning, for gastropods, in the Lower Cambrian.
Naturalist, 1906, pp. 7 6 9-795, 82 9- 8 59) finds that foremost in the long series of causes which lead to extinction are the grander environmental changes, such as physiographic changes, diminished or contracted land areas, substitution of insular for continental conditions; changes of climate and secular lowering of temperature accompanied by deforestation and checking of the food supply; changes influencing the mating period as well as fertility; changes causing increased humidity, which in turn favours enemies among insect life.
In other words, a balance appears to be always sustained between the internal (hereditary and ontogenetic) and the external (environmental and selectional) factors of evolution.
These attempts to reject environmental variation rest on several grounds.
Such cases show in the plainest way the co-operation of external or environmental and internal or constitutional factors.
The old organism is more stable and responds in obvious ways to direct assaults from without; the young organism is at once less stable and more profoundly modified by environmental change, replying in terms less easy to predict from knowledge of the nature and amount of the impinging agency.
And finally, there are a series of variations, amongst which no doubt are the mutations of de Vries and the disintegrations and recombinations of the unit factors with which Mendel and his followers have worked, in which the external or environmental factor is most remote from the actual result.
Cossar Ewart, "Variation, Germinal and Environmental," in Trans.
And greener (in the environmental way, not the color way).