(Darwin 1897, 233-234) said: “Until man selects birds differing in the relative length of the wing-feathers or toes (and so on), no sensible change in these parts should be expected. Nor could man do anything unless those parts happened to vary under domestication: I do not positively assert that this is the case…”.
On page 235, He (Darwin, 1897) continues: “The progress of selection almost inevitably leads to the neglect and ultimate extinction of the earlier and less improved forms, as well as many intermediate links in each long line of descent.”
It truly does appear that by his language, Darwin is fueling his “descent with modification” theory strongly based upon his observances in artificial selection (man’s husbandry) with pigeons.
When looking at the possible outcomes of a Punnett square, even with only one trait involved, sometimes there is 100% chance of a certain phenotype (outward appearance) manifesting and sometimes there is a 25% chance. Without bringing epigenetics into the picture, there is an element of DNA recombination between a sperm and egg that is random. Random and not “selected.” With that being said, I believe epigenetics is showing how certain traits (after their own kind/within a species) can be selected by nature, due to “external locks and unlocks” placed on the genome.
In pop culture, we have seen plenty of pictures of dramatic jumps from one type of animal to another type of animal, suggesting macroevolution. I find it interesting that Darwin said in the first entry I quoted that man’s artificial selection could not in effect, be performed on something (a trait) that was not already there. “Nor could man do anything unless those parts happened to vary under domestication (Darwin 1897, 233-234).” Darwin’s words came in light of what he observed in artificial selection with intelligent input from man, resulting in creatures “after their own kind.”
My thinking, which is not original, is that Darwin at least somewhat based his theory of evolution upon what he witnessed in mankind’s artificial selection within certain lines of animals (and plants), in this case pigeons. Many of the “changes” Darwin witnessed, after their own kind, required intelligent input and not random action.
Darwin, Charles. The variation of animals and plants under domestication, Volume I. New York: D. Appleton and Company, 1897.