Which discovery encouraged the Leakeys to continue looking for human remains at Olduvai Gorge?

The discovery of a hominin skull in 1959 at Olduvai Gorge by Mary Leakey encouraged the Leakeys to continue their search for human remains. This skull, known as "Nutcracker Man" or Paranthropus boisei, demonstrated the significance of the site for understanding human evolution and motivated further excavations.