Lucy: Australopithecus afarensis

Australopithecus afarensis existed between 3.7 and 3 million years ago. This species, with its remarkable bipedal locomotion, played a pivotal role in shaping our understanding of human evolution, from the early days of upright walking to the nuances of growth, development, and dietary adaptations. The taxonomic and phylogenetic research in paleoanthropology, which experienced a renaissance around the time of afarensis' discovery, has benefited from the extensive baseline data on skeletal and dental variation provided by the Hadar site sample. Several debates persist, including the nature of terrestrial bipedality, the degree of sexual dimorphism and its implications for social behaviour, and the structure of the phylogenetic tree before the emergence of Homo and robust australopith lineages. Lucy is a famous hominin fossil, discovered in 1974 by paleoanthropologist Donald Johanson in the Afar region of Ethiopia. Her skeleton was about 40% complete, and was a ground-breaking find, making her one of the most complete early hominins known at the time. The excavation took three weeks, revealing forty-seven out of 207 bones, including parts of the arms, legs, spine, ribs, pelvis, lower jaw, and skull fragments. Notably, there were no duplicate bones, indicating they belonged to a single individual. Lucy's pelvic bones indicated she was female. Despite her small stature of 1.05 meters and an estimated weight of 28 kilo grams, certain features suggested she was a young adult. The nickname "Lucy" comes from the Beatles' song "Lucy in the Sky with Diamonds," which the team often played at their camp. Formally known as A L two eight eight dash one, Lucy's age is around 3.18 million years. Initially, Johanson thought she might be a small member of the genus Homo or a small australopithecine. However, further analysis of nearby fossils and those from Laetoli in Kenya led scientists to establish a new species, Australopithecus afarensis, four years after Lucy's discovery. At that time, afarensis was considered the oldest known hominin species, although more ancient species have since been found. The taxon Australopithecus afarensis was suggested for all Hadar specimens. The Laetoli footprints, about 70 in total, suggest that these hominins walked in a manner more similar to humans than apes. Their foot structure, gait, and biomechanics resembled those of modern humans, although their legs may have been slightly more bent at the knee. The footprints also reveal intriguing social dynamics. Different-sized feet indicate a small group walking from south to north, with a smaller individual stepping into the footprints of a larger one. Another set of footprints, discovered 40 years later, showed a larger individual walking alongside smaller ones, suggesting a social group comprising a large male, females, and children. The Laetoli footprints provide valuable insights into the behavior and anatomy of early hominins, shedding light on their social structures and walking patterns. The well-preserved condition of Lucy's fossils allowed scientists to study her morphology and draw certain conclusions. Lucy's size was confirmed by other Hadar remains, indicating a smaller stature compared to modern humans. The length ratio of her humerus to femur suggested longer arms relative to legs, a feature not seen in current humans. The hand and foot bones of Lucy and related specimens differed from those of contemporary individuals. The structure of Lucy's hip suggested a bipedal posture, a significant aspect of her morphology. One notable missing part of Lucy is her face, as only a few cranial fragments were found. Reconstruction of her cranium involved combining fragments from different specimens, making the calculation of cranial capacity less precise. Nevertheless, it was evident that individuals like Lucy had a very small brain. It's important to note that Lucy's bipedalism, once emphasized, is now seen in a context different from modern humans' walking style. Lucy revealed bipedalism with a chimpanzee-like cranial size. This insight challenges earlier ideas and contributes to our understanding of early human evolution, highlighting the coexistence of bipedal locomotion and smaller brain size in our ancestors. Australopithecus afarensis, like Lucy, showed a mix of both primitive and more advanced traits, making them a great example of mosaic evolution. Some features, such as their hip shape, were advanced and similar to later hominins, indicating a closer relationship. On the other hand, certain traits, like their V-shaped dental arcade (different from our parabolic one), longer arms, and their small, robust brain, were more primitive. Despite having a small brain, afarensis had a pelvis and leg bones that functioned similarly to modern humans. In simple terms, they were like "ape-brained" creatures with body structures suited for walking on two legs.