They seem to have been deliberately selected and placed at specific points in the circle that mark certain calendrical events (sunsets and solstices related to the four seasons, for example).
He was oftener selected because of his muscular development than on account of his scholastic attainments, though both were considered essential to complete success.
They were selected on the basis of their phylogenetic positions and their specific interest as human pathogens, or as industrially or environmentally important yeasts.