Let's take a paragraph from the original source, which is only three paragraphs before the one you quote-mine:
Even a superficial glance is sufficient to show that all the innumerable forms in which the life-urge of Nature manifests itself are subject to a fundamental law – one may call it an iron law of Nature – which compels the various species to keep within the definite limits of their own life-forms when propagating and multiplying their kind. Each animal mates only with one of its own species. The titmouse cohabits only with the titmouse, the finch with the finch, the stork with the stork, the field-mouse with the field-mouse, the house-mouse with the house-mouse, the wolf with the she-wolf, etc.
Deviations from this law take place only in exceptional circumstances. This happens especially under the compulsion of captivity, or when some other obstacle makes procreative intercourse impossible between individuals of the same species. But then Nature abhors such intercourse with all her might; and her protest is most clearly demonstrated by the fact that the hybrid is either sterile or the fecundity of its descendants is limited. In most cases hybrids and their progeny are denied the ordinary powers of resistance to disease or the natural means of defence against outer attack.
Isn't the very *definition* of species, related to whether or not mating results in offspring, or more precisely, of fertile offspring?
And as for your assertion that
"Hitler was a rather strict Creationist - he doesn't even allow that a canine “kind” could give rise to foxes, dingos, coyotes, and wolves - all in record time when needed. Nope - to him “a fox is always a fox”.
try to reconcile that with the paragraph before the one you posted:
Such a dispensation of Nature is quite logical. Every crossing between two breeds which are not quite equal results in a product which holds an intermediate place between the levels of the two parents. This means that the offspring will indeed be superior to the parent which stands in the biologically lower order of being, but not so high as the higher parent. For this reason it must eventually succumb in any struggle against the higher species. Such mating contradicts the will of Nature towards the selective improvements of life in general. The favourable preliminary to this improvement is not to mate individuals of higher and lower orders of being but rather to allow the complete triumph of the higher order. The stronger must dominate and not mate with the weaker, which would signify the sacrifice of its own higher nature. Only the born weakling can look upon this principle as cruel, and if he does so it is merely because he is of a feebler nature and narrower mind; for if such a law did not direct the process of evolution then the higher development of organic life would not be conceivable at all.
And a couple of paragraphs later he says:
If the case were different the progressive process would cease, and even retrogression might set in. Since the inferior always outnumber the superior, the former would always increase more rapidly if they possessed the same capacities for survival and for the procreation of their kind; and the final consequence would be that the best in quality would be forced to recede into the background. Therefore a corrective measure in favour of the better quality must intervene. Nature supplies this by establishing rigorous conditions of life to which the weaker will have to submit and will thereby be numerically restricted; but even that portion which survives cannot indiscriminately multiply, for here a new and rigorous selection takes place, according to strength and health.
This is by definition survival of the fittest.
The difference, since you seem unable to grasp it, is that Adolph reasoned that changes in kind only came about by breeding of different kinds to create a new kind, whereas "evolution" suggests that changes come about by random changes in the allele -- but both are subject to selection pressures.
And it is the selection pressure which Adolph uses as his excuse for racism. As he writes in the next paragraph:
If Nature does not wish that weaker individuals should mate with the stronger, she wishes even less that a superior race should intermingle with an inferior one; because in such a case all her efforts, throughout hundreds of thousands of years, to establish an evolutionary higher stage of being, may thus be rendered futile.
To recap:
Evolutionists claim that the diversity of species results from random changes to the allele coupled with selection pressure leading to differentially greater chances for survival and hence reproduction among the offspring who happen to have characteristics more conducive to survival in a local environment; that such characteristics become dominant within a species over time; and that when enough genetic changes accumulate, representative individuals who possess enough of those changes become mutually infertile with members of the population who do not -- hence the "origin of species".
Hitler was only an amateur painter and dictator, we have no evidence he was a serious student of biology. He seemed to think new races came about by breeding of existing disparate populations or kinds; and that nature herself rejected the miscegenation of the stronger by making the offspring infertile, thereby preserving purity of races; and that if by any chance the offspring *were* fertile, they would represent a dead end since they did not have the survivability of the "stronger" parent.
In both cases, then, the action of culling by external actors applies: in the one case a nebulous 'fitness' function, in the other case strength and health (which are probably pretty well correlated with "fitness" btw, if one reads the endless articles in popular magazines about how people choosing mates based on appearance has an evolutionary origin and component...)
What Adolph did was to emphasize the fitness part and use it as a springboard for racism and eugenics. It is the philosophical feature of "survival of the fittest" taken out of its scientific context within evolutionary theory which served as the underpinning for this.
(Incidentally, the other feature of 'selection pressure' which lends itself to eugenics is its strictly statistical nature, with no notion of mercy, compassion, or forgiveness. Those who wish to engage in cruelty will always have an easier time justifying their actions by pointing to nature as a guide, since morality as expressed in Christianity is simply unknown when considering selection pressure per se The error consists in assuming or insisting that a model construct useful for approximating statistical populations of biological entities, is either an adequate reflection of, or a normative guide to, conscious behaviour of sentient beings within a socio-historical context.)
Cheers!