There is something here that is much more general than this particular issue: dictionary definitions of scientific concepts (and those in many other fields) are

There is something here that is much more general than this particular issue: dictionary definitions of scientific concepts (and those in many other fields) are merely summaries, and far from being the last word on the matter (you can't learn quantum mechanics from a dictionary.) It is not uncommon, in forums like HN, for there to be arguments over the 'true' definition of a word, but unless the issue being debated is lexicographical, these arguments are usually missing the point. While it is the case that the teaching of a subject often begins with some definitions, that is only the beginning, and it is usually done to shortcut the difficult process by which those definitions came to be written in the first place. On reflection, it should be clear that the definitions cannot be written (or, at least, finalized) until after we have gained an understanding of that which we are defining. What we are observing here is the selection part of evolution. We did not observe the origination of the mutation causing the trait being acted on by selection, but it is empirically established that it is not uncommon for such mutations to occur. Nor have we seen it play out fully, where the trait, and the mutation causing it, become ubiquitous, and other alleles disappear (if the selection pressure continues and the species does not become extinct.) Here, we are observing evolution in progress, not its ultimate result. This change alone will not create a new species, but if enough changes occur that the descendants could not, in principle, breed successfully with their ancestors, then it has. We can see a precursor to this in the mutation being lethal in males.