There’s an annoying Darwin quote-mine that’s come up recently in a Discovery Institute video. But I’ve seen it many other times, sometimes from non-creationists, even biologists.
The commonly quoted bit (page 184; all quotes from the 1st edition of the Origin):
In North America the black bear was seen by Hearne swimming for hours with widely open mouth, thus catching, like a whale, insects in the water. Even in so extreme a case as this, if the supply of insects were constant, and if better adapted competitors did not already exist in the country, I can see no difficulty in a race of bears being rendered, by natural selection, more and more aquatic in their structure and habits, with larger and larger mouths, till a creature was produced as monstrous as a whale.
The video proceeds to laugh at Darwin for suggesting that whales evolved from bears and shows evolutionary biologists laughing at Darwin for the same thing. (It then proceeds to laugh at the evolutionary biologists, but that’s another subject.)
But if you read carefully, Darwin wasn’t suggesting a line of descent at all, merely a scenario for possible future adaptation. He’s not saying that bears turned into whales. He’s saying that a population of bears, in a particular environment with a particular food source, might end up converging on a whale-like phenotype. Not clear from the quote? Then consider the context. Here’s the beginning of the paragraph, setting up this and other examples and explaining the point (page 183):
I will now give two or three instances of diversified and of changed habits in the individuals of the same species. When either case occurs, it would be easy for natural selection to fit the animal, by some modification of its structure, for its changed habits, or exclusively for one of its several different habits. But it is difficult to tell, and immaterial for us, whether habits generally change first and structure afterwards; or whether slight modifications of structure lead to changed habits; both probably often change almost simultaneously.
And here (page 179) is the title of the section, introducing the subject.
On the Origin and Transitions of Organic Beings with Peculiar Habits and Structure
Finally, here’s the beginning of the chapter (page 171)
CHAPTER VI. DIFFICULTIES ON THEORY. Difficulties on the theory of descent with modification — Transitions — Absence or rarity of transitional varieties — Transitions in habits of life — Diversified habits in the same species — Species with habits widely different from those of their allies — Organs of extreme perfection — Means of transition — Cases of difficulty — Natura non facit saltum — Organs of small importance — Organs not in all cases absolutely perfect — The law of Unity of Type and of the Conditions of Existence embraced by the theory of Natural Selection.
(The relevant portion of the chapter summary is in bold.)
And here’s relevant sentence from the introduction to the chapter (stil page 171):
Secondly, is it possible that an animal having, for instance, the structure and habits of a bat, could have been formed by the modification of some animal with wholly different habits?
So why is the bear mentioned? It’s not a phylogenetic hypothesis at all. It’s an example of a change in behavior potentially creating what we would now call an altered selective regime, which Darwin suggests could result in considerable divergence from the ancestral phenotype. It’s one of several such examples embedded in a discussion of that subject. If this is something you’ve been thinking Darwin was wrong about — and certainly he was wrong about some things — then you should stop.
(Quotes from the Origin were pulled from the handy Darwin-Online site; that link takes you right to the spot.)