This drying trend led to the separation of an ape population in eastern Africa from other populations of apes in the more heavily forested areas of western Africa.The eastern population had to adapt to drier, open savanna environments, which favored the evolution of terrestrial living.This chapter introduces students to the development of the hominid line. An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.
Criticism of the savanna hypothesis has spawned alternative ideas about early human evolution.
The woodland-mosaic hypothesis proposes that the early australopiths evolved in a mosaic of woodland and grassland that offered opportunities for feeding both on the ground and in the trees.
It is possible that these fossils belong in the hominid family, or they may be representatives of the ancestors of the chimpanzees/bonobos, or they may represent forms for which there are no modern descendants.
This species is known for only a single skull, found in Chad in Central Africa. The hominid-like traits include nonhoning canine teeth and a foramen magnum positioned at the base of the skull, indicating that is was (most likely) bipedal.
These important evolutionary changes would have depended on increased mental abilities and, therefore, may have correlated with the development of larger brains in early humans.
Critics of the savanna hypothesis argue against it on several grounds, but particularly for two reasons. afarensis has been found in Chad in west-central Africa, 2500 kilometers west of the African rift valley.
However, the cranial capacity is small and within the range of chimpanzee/bonobo, it has a huge brow ridge, and the enamel on its premolars and molars is thinner than found in other hominids.
Both cranial and post-cranial elements have been found at Lake Turkana, Kenya.
This find suggests that australopiths ranged widely over the African continent and that East Africa may not have been fully separated from environments further west.
Second, there is growing evidence that open savannas were not prominent in Africa until sometime after 2 million years ago.
There are many ideas about why the early australopiths split off from the apes, initiating the course of human evolution.