This section is from the book "Nature's Garden", by Neltje Blanchan. Also available from Amazon: Nature's Garden; An Aid To Knowledge Of Our Wild Flowers And Their Insect Visitors.
"All variations which render the blossoms more attractive, either by scent, colour, size of corolla, or quantity of nectar, make the insect visit more sure, and therefore the production of seed more likely. Thus, the conspicuous blossoms secure descendants which inherit the special variations of their parents, and so, generation after generation, we have selections in favour of conspicuous flowers, where insects are at work. Their appreciation of colour, because it has brought the blossom possessing it more immediately into their view, and more surely under their attention, has enabled them, through the ages, to be preparing the specimens upon which man now operates; he taking up the work where they have left it, selecting, inoculating, and hybridizing, according to his own rules of taste, and developing a beauty which insects alone could never have evolved. His are the finishing touches, his the apparent effects; yet no less is it true, that the results of his floriculture would never have been attainable without insect helpers. It is equally certain, that the beautiful perfume, and the nectar also, are, in their present development, the outcome of repeated bisect selection; and here, it seems to me, we get an inkling of a deep mystery: Why is life, in all its forms, so dependent upon the fusion of two individual elements? Is it not, that thus the door of progress has been opened? If each alone had reproduced, itself all-in-all, advance would have been impossible; the insect and human florists and pomologists, like the improvers of animal races, would have had no platform for their operation, and not only the forms of life, but life itself would have been stereotyped unalterably, ever mechanically giving repetition to identical phenomena." - Frank R. Cheshire in "Bees and Bee-keeping."