Discovering our most famous ancestor

	What is Evolution?
	Lucy's Discovery

On November 24, 1974 after a long hot morning of surveying for fossils, Donald Johanson and Tom Gray made the discovery of a lifetime. Searching in a maze of ravines at Hadar in northern Ethiopia, Johanson spotted a tiny fragment of arm bone on the ground that he quickly identified as a hominid – an ancestral member of the family of humans. Looking up the slope, he saw a skull bone, then a femur, some ribs, a pelvis and the lower jaw.

After extensive screening and sorting, the team unearthed 47 bones of a skeleton - nearly 40% of a hominid that had lived approximately 3.2 million years ago.

Its small size and the shape of its pelvis identified the skeleton as female. In life, she would have stood approximately 3.5 feet tall and weighed between 60 to 65 pounds. To this day, Lucy remains the oldest and most complete adult human ancestor fully retrieved from African soil.

An Inspired Name

Technically, she was known as AL-288. But during the celebration on the night of her discovery, the Beatles song “Lucy in the Sky With Diamonds” was played over and over. Someone suggested she be named Lucy and the name stuck. The Ethiopian people refer to her as “Dinkenesh,” an Amharic language term meaning “You are beautiful.”

An entirely new species

The discovery of Lucy yielded an entirely new species of human ancestor, known as Australopithecus afarensis, or “southern ape of Afar,” after the region of Ethiopia where the bones were found. To determine if a fossil represents a new species, paleoanthropologists compare it to known samples, noting the similarities and differences. Then, using knowledge of evolutionary processes as well as anatomy and biology, it is determined whether the differences are significant enough to distinguish a new species.

How do we know she was a she?

The fossil known as Lucy was determined to be female based on several traits:

• Lucy’s small size compared to other representatives of the same species.
• The shape of her pelvis compared to the pelvis of the larger individuals.
• Lucy’s small size is seen as an expression of “sexual dimorphism.” This terminology refers to the difference in shape between individuals of different sex in the same species. For example, in mammals, the male is larger than the female.
• The first complete male afarensis skull was discovered in 1994, less than ten kilometers from the site of Lucy’s discovery. An analysis of the skull indicated that afarensis males were twice the weight of females.

The Controversy Continues

The discovery of Lucy continues to profoundly influence our understanding of human origins. “Lucy’s Legacy” provides people the opportunity to better understand current scientific theory of human evolution and to see for themselves how, more than 30 years after her discovery, she continues to create debate.