I do not say 'fittest,' because it is ordinarily understood to mean that the survivors have some morphological features, by which they are benefited, which lead on finally to specific characters.
I do not find this to be the case. Take an instance of great contrast. Sow 100 seeds of the water (submerged) Ranunculus fluitans in a garden. They all grow up as aërial plants, i.e. they vary as they grow precisely in the same way. It is only the weakest (from badly nourished seeds) which get crowded out of existence. Here, then, is definite variation without the aid of natural selection. Ex uno disce omnes.
2. Delimitation of varieties and species by the non-reproduction of intermediate forms.
It is generally said that if 'good species' are isolated, the intermediate forms have been killed off by natural selection. I maintain that they were never reproduced. Thus if A has passed by successive generations, A′, A″, A‴, &c., to An; A and An being now only in existence, then A′, A″, &c., represented a single generation apiece, each offspring being one degree nearer to An, but could never be reproduced, as the environment was continually acting upon the whole series, urging each generation forwards till it became stable in An.
This is precisely what takes place in cultivating a wild plant like the parsnip. Each year the grower selects a slightly improved form, till the required type is fixed. The 'Student' is now An, a more or less permanently fixed form, each of the intermediate forms, lasting one year, having ceased to be reproduced.
3. The geographical distribution of varieties and species by self-adaptation.
That is, if a number of plants migrate to a new locality with new environmental conditions, half of them may die; because they cannot adapt themselves; the other half may live—change, and become fixed forms, by their power of adaptation. The final conclusion of the whole is that plants require nothing more than climatic influences, to which their protoplasm may respond. The result is new varietal or specific characters. Then, if the same environment lasts, these become gradually more and more fixed and hereditary, but one can never tell beforehand but that the oldest plant in creation may not change again as soon as it finds a new environment.... This is what a long study of plants and experiments has led me to; and it is not a conclusion arrived at solely by 'thinking out' or evolving from my own consciousness—like the German camel!
Hoping you are progressing,
Believe me, yours sincerely,
George Henslow.