11 – The discovery of Lucy

3.2 million years ago

Lucy, a female hominin living in an area of the African Rift Valley, died on a riverbank over 3.18 million years ago. Sediment quickly covered her little body, and her bones were preserved there until she was discovered by Donald Johanson and Tom Gray in 1974. It was a remarkable find, and Lucy continues to be such an important fossil specimen because so much of her skeleton was preserved, and her species, Australopithecus afarensis, is the first ancient ancestor that scientists believe walked upright, bipedally, all the time.

Evidence of obligate bipedalism in Lucy’s species includes a broad pelvis and gluteal muscle attachments that indicate Au. afarensis was capable of hip abduction, a stabilizing condition that makes bipedal striding smoother and more efficient. There is also an increased surface area in her knee joint for greater load bearing. Lucy has become a symbol of adaptability, ingenuity, and innovation in our ancestors.

Image courtesy ASU Institute of Human Origins.


    Pliocene5.3 to 2.58 million years ago

Environmental and Climate Changes

  • Continued aridity, enhanced seasonality—Loss of forests and savanna expansion 4.4 Ma
  • Shifts to even more open and arid environments 3 to 2.5 Ma

Changing Species