The Lucy skeleton provided much information concerning A. afarensis. For one thing, the species had curved phalanges, which means the creature was an agile tree-climber. Scientists believe that trees offered much-needed protection from predators and supplied fruit, and thus the tree-climbing adaptation. A group of scientists have proposed, however, that A. afarensis was not habitually bipedal; rather, it spent the majority of its time as a quadruped and on the branches of trees. Others, such as Owen Lovejoy, believe the curved phalanges to just have been a throwback trait, unevolved, in the adoption of bipedalism. He reasoned that, sometimes, while one part evolves, another does not, but the part that does not evolve does not interfere with the part that does evolve.
It is very likely that A. afarensis lived in small foraging social groups, such as in modern chimpanzees and gorillas. The fossils of 13 individuals have been found together at Hadar, known as the First Family, and are thought to have died together. On the evidence of teeth, this creature was clearly omnivorous, with a diet of fruits and other soft foods.
A. afarensis had many ape-like aspects of its anatomy. For example, the humerus-femur ratio is approximately that of a chimpanzee: 95%. That means that the arm is almost as long as the leg. In humans, this ratio is only 70%. There was also strong sexual dimorphism in this species, with the males almost twice as bulky and large as the females. This is a sign of polygamy and is taken to be evidence that males competed with each other for mating privileges with females. However, there is no large and protruding canine in A. afarensis, and thus, maybe they seldom fought. Their chewing muscles are also similar to those of a chimpanzee. Furthermore, their rib cages had a conical shape.
At this stage, the brain still shows no sign of enlarging: A. afarensis' cranial capacity was still around 450 cc. Instead, it is mainly in the teeth that we see the vast majority of the change taking place (the pelvis and leg bones are already nearly humanlike): The canines are smaller than in A. anamensis, and there is the usual early-hominid V-shape of the dental arcade, halfway between the rectangular shape in apes and the parabolic one found in humans. Their molars are large with thick enamel.
Despite detailed research, there are still differing views of the exact role A. afarensis played in the evolution of humans. Its true identity and place in our family trees are still subjects of confrontation and debate among paleoanthropologists. It may be a while before the conflict is resolved.
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