When Donald Johanson and his colleagues returned to the Afar region of Ethiopia in 1974 they were full of optimism. It was their second season searching for human fossils around Hadar.
The previous November Johanson had found a fossilised knee joint that was dated to more than 3 million years ago. When the tibia and femur was put together it was clear that they were from an upright walking hominid. In apes the leg bones form a straight line but in humans the joint is angular. This was the first fossil of it's kind from this age and gave hope that there was more to come.
The 1974 season started promisingly with the discovery of a hominid jaw but little else. Then on 24th November Johanson and a colleague were returning to the Land Rover at a site more than a mile from the location where the knee had been found the previous year. Johanson spotted an arm bone on the slope of a gulley. Beside it he quickly found a part of a skull, a femur, some ribs a pelvis and lower jaw.
That evening there was a party back at the camp with colleagues from America, Britain and France as well as local guides and guards. The tape that was played loudly and repeatedly included the Beatles' "Lucy in the Sky With Diamonds". Confident that the fossils belonged to a female hominid they decided to christen her Lucy.
Careful searching and sifting over the next few weeks turned up several hundred bone fragments making up 40% of the skeleton. Lucy was young but sexually mature - probably about 12 years old at the time of her death. She does not seem to have died as a result of violence. She was about three and a half feet tall and weighed around 60 pounds. Her arms were similar in length to a modern human but that is obviously long in proportion to her height.
Due to the volcanic layers above and below the strata where Lucy was found dating her remains has proven to be very consistent using Argon-Argon radiometric dating.
Lucy is the most famous specimen of a species known as Australopithecus afarensis - "Southern Ape from Afar". Her skeleton has lots of evidence showing that she walked upright. The knee joint was capable of locking straight. Apes never fully straighten their knees because they can't. Try standing or walking with slightly bent knees and see how long you last.
The femur was angled in relation to the condyles - the knobbly bits on the end of the bone. This angle makes it possible to balance on one leg at a time while walking. The condyles are large to support the load of bipedal walking. The big toe has come into line with the other toes unlike the splayed big toe of apes. Even her spine shows evidence of the curves that we all have to accommodate our upright posture.
Since 1974 the fossil remains of more than 300 of Lucy's species have been found. Australopithecus afarensis lived between 3.85 and 2.95 million years ago in Eastern Africa.
They had both ape and human characteristics with apelike face proportions and a small brain, usually less than 500 cubic centimeters -- about 1/3 the size of a modern human brain. They had long, strong arms with curved fingers adapted for climbing trees. They also had small canine teeth like all other early humans. Their adaptations for living both in the trees and on the ground helped them survive for almost a million years as climate and environments changed. The species survived for more than 900,000 years, which is over four times as long as our own species has been around.