Notice the part where it says "or", which implies one or the other:
It's not uncommon to see "or" used to combine alternate titles for the same work in writing from the 1800's. There's a difference in its use simply as a conjunction vs its use as a logical operator.
The dropping of this second part of the title should raise a flag.
Should the dropping of the second half of the first clause of the title not also raise a flag, then? I mean, there must be some kind of insidious meaning behind "by Means of Natural Selection", right? Wow, and now I see that many modern print editions are dropping the "On" from the title! Why would they do that? Let's see... "o" is the 15th letter of the alphabet, and "n" is the 14th... and if you add them together you get 29... which is a prime number... and if you add 2 and 9, you get 11... That's it! 2 9/11! They're saying there's going to be a second 9/11 attack by removing the first word of the title of a book written in the 1800's!
Or, sometimes, a cigar is just a cigar, to paraphrase Freud.
