Final answer:
Piltdown Man was initially accepted because it fit with European-centrist views of human evolution, while the African fossils of Pithecanthropus and Australopithecus were rejected due to their location and primitive features. Over time, the accumulation of fossil evidence led to the rejection of Piltdown and the acceptance of the true human ancestors.
Step-by-step explanation:
The reason Piltdown Man was accepted for so long is due to the biases and expectations of the scientific community at the time. Its discovery in England fit neatly with contemporary views that modern humans originated in Europe. On the other hand, specimens such as Pithecanthropus (now known as Homo erectus) and Australopithecus were initially rejected as human ancestors because they were discovered outside Europe, and their primitive features didn't align with the then-prevalent belief of a linear progression of human evolution.
Pithecanthropus and Australopithecus were indeed ancestral to modern humans, unlike the fraudulent Piltdown. Australopithecus species, such as Australopithecus afarensis and Australopithecus africanus, were bipedal and had a mix of primitive and advanced features. They date back to between two and three million years ago, with brain sizes roughly between 400 and 500 cubic centimeters. Over time, as more fossil evidence was accumulated and knowledge advanced, the scientific consensus moved away from Piltdown Man and understood the true significance of Pithecanthropus and Australopithecus in the human lineage.