Written by: Xuân Phi, 05/08/2022
Supported by: Ex-BC Examiner, 06/08/2022
Question: The diagram shows the skeletal systems of two ancestors of modern human beings. Summarise the information by selecting and reporting the main features, and make comparisons where relevant.
The diagram depicts the skeletal structures of two early hominins, namely the Australopithecus afarensis and the Homo erectus. As can be seen from the picture, the Australopithecus afarensis is bigger in size and possesses longer arms more suited to climbing compared to the Homo erectus which has a slimmer body to facilitate long-distance running.
Regarding the Australopithecus afarensis, the structure of its upper body is larger. More specifically, the massive skull and the long snout contribute to its unbalanced head. Additionally, the Australopithecus afarensis has high and narrow shoulders with a wide chest as well as a short and wide waist. The length of the arms almost reaches the knees due to the long forearms and large palms. The lower part of the body consists of a small gluteus maximus and a long femoral neck. The joints for the hip, knee and ankle are small, while the Achilles tendon is short and the heel bone is similarly small. Finally, the toes are long with a partial foot arch.
Shifting to the Homo erectus, the head is more balanced with a shorter snout. Compared to the Australopithecus afarensis, the shoulders are lower and broader, but the chest and waist are smaller. The arms are shorter due to the short forearms. Furthermore, the Homo erectus has a large gluteus maximus and a short femoral neck. The hip, knee, and ankle joints are relatively enlarged, with an extended heel bone and a lengthy Achilles tendon, allowing for improved running and walking. Finally, the foot arch is stabilized through shorter toes.
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