Final answer:
Current evidence suggests that the last common ancestors of hominins and African apes lived between 5 to 7 MYA, with species like Sahelanthropus tchadensis and Australopithecus providing significant insights into hominin evolution.
Step-by-step explanation:
Current evidence suggests that the last common ancestors of hominins and African apes lived approximately around 5 to 7 million years ago (MYA). The discovery of the complete cranium of Sahelanthropus tchadensis in Chad by Michel Brunet's team provides valuable insights into this period. This species, which lived right at the time of the divergence, had a cranial capacity similar to a chimpanzee and did not exhibit clear signs of bipedalism, which is a significant characteristic of later hominins.
The genus Australopithecus, evolving about four million years ago, represents a later stage in hominin evolution with their development of bipedalism. Fossils like the famous "Lucy" reveal a mixture of ape-like features and characteristics more common to later hominins. Males of this genus showed greater sexual dimorphism than in modern humans, similar to that seen in gorillas and orangutans. Despite a smaller brain size relative to body mass when compared to modern humans, they were bipedal and potentially spent time in trees as well.