The style of the piece and the citation of his degrees made me think it was published somewhere, but I saw no citation on the site.
No citation because (a) it was published on Selby's site first and (b) it's his intellectual property and does not require a citation. It was submitted to multiple publications. Whether or not they choose to publish it is out of Selby's hands, but he can control what goes on his personal site, so he made sure it at least appeared there.