[Orgmode] Recursive org-agenda-files

[Matthew Lundin]

Is it possible to set the org-agenda-files variable to include all org
files within a directory recursively?

I currently use:

(set org-agenda files (file-expand-wildcards "~/org/*.org"))

This, of course, includes all org files in ~/org. 

But how would I include all org files in both ~/org and
its subdirectories without having to enter them all by hand?

E.g.,

    org/
        (.org files here)
        professional/
            (.org files here)
            research/
                (.org files here)
            teaching/
                (.org files here)
        personal/
            (.org files here)
        computer/
            (.org files here)

Thanks!

Matt Lundin