Pre-populating field content

I have a channel with a radio button field that I pre-populate from content from another channel. When I go to enter data into Publish the pre-populated radio buttons don’t sort alphabetically. They, of course, populate by most-recent entry into that other channel.

For instance, I have two channels: Author and Book. Author has the names of authors and Book has book information, including the author’s name (pre-populated from Author).

I enter into Author: - John Doe - Alan Johnson

And the radio button content in Book has authors as: - John Doe - Alan Johnson

Is there a way to change the default sort from entry date to alphabetical (presumably by title)?