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“Varieties… are just ‘incipient species,’ and what normally turns two varieties into two species is not that presence of something… but the absence of something: the intermediate cases” (Dennett 45).  I do agree with Dennett that in many cases of speciation, the species exist because the intermediate species no longer exist.  I do not agree, however, that there is no extra presence of something, like a gene, that makes the two species different. 

He is suggesting that there is a line of organisms, each more evolved than the one behind it, but the middle organisms in the line are extinct, and there is no extra presence of something that makes the first organism in the line different from the last.  Without that difference, the two organisms (first and last in the line) would just be varieties of the same species. 

I am probably being overly picky about his choice of words, but honestly, he is writing a book about evolution and the word that I felt was misused was italicized in his text.  So, I had to take advantage of the situation.

Andrea Zambetti