[AndrewC]

Not when the person's character is at the center of the issue. Dawkins was defending himself against scurrilous attacks that his science was a result of his alleged politics

It certainly is when Gould was not the writer of the article to which Dawkins was responding.

[CarolinaGuitarman]

"It certainly is when Gould was not the writer of the article to which Dawkins was responding."

So? The writer of the article was comparing Gould and Dawkins. Their differences was the issue of Bradley's article, with Bradley taking Gould's side exclusively. Bradley's arguments were all from Gould. In order to defend himself from Bradley, he had to simultaneously correct Gould's errors as well. Was he snippy? I would be too. Was it ad hominem? Only if you redefine ad hominem.