I believe Athena was a Greco-Egyptian, descended from IO. Pausanias tells us about Danaus building a temple to Athena from Sais, called Neith. Cicero gives us her genealogy.

Additionally, Cicero mentions 3? other Athena's, so there is definitely a Greek Lady who was deified as Athena as well. I have traced the timeframes of these other Athena's on this site before, but that is irrelevant.
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I have not read 'Black Athena'. The title of "Black" means something. It could be like "Kemi", which has been discussed before. However, in this 1-page-article, the term "Arian" appears. So it appears this guy is race-bating, regardless of what his work actually says.

The guy could have used a title like... "Egyptian Athena"... or "Athena Stolen" or a number of other titles, but he didn't. Maybe the title sells books, but it also invites criticism.

Note: I have read a few pages of excerpts of this book (Amazon or books.google.com); it seemed easy to understand... I saw some good info on the funerary statue of Amenhotep 3 by Edel.