By John Ostapkovich

PHILADELPHIA (CBS)  –  As the whole world awaits the selection of the next Pope, a LaSalle religion professor is focusing on the un-sung heroes of the Church.

From Nunsense to Sister Act, (and who could forget The Flying Nun?), women religious have been celebrated and also featured in more serious fare.

LaSalle Religion Professor Margaret McGuinness has taken a look at centuries of impact in “Called to Serve: A History of Nuns in America.”

She says nuns were the backbone of creating the parochial schools, and today have a more diverse focus serving any in need.

Just as there’s a priest shortage, there is a shortage for nuns.

McGuinness says ”the numbers have gone down dramatically since somewhere in the mid-1960′s which was really the peak year and now that the number has gone down, the average age has gone up. Women used to enter religious life at 18 to 20. Now they tend to be in their thirties.”

McGuinness aims for a general audience in tracking nuns from their arrival in 1727 through today, even if they don’t sing much.