Executive Director Neils Agather says the value of the sculptures now far exceeds anything that could justify owning them. The foundation's mission is to support activities in the community, not own art.
Several casts of each were made. One sold in November for $48 million.
The Fort Worth Star-Telegram reports the Kimbell Art Museum will receive two other works from the foundation, Henry Moore's "Figure in Shelter" and Fernand Leger's "La Fleur qui Marche."
Sotheby's is organizing a private sale for "The Backs."