Final answer:
Adaptations to savannah life such as upright bipedalism, dietary shifts, and tool use explain the anatomy and behavior of Homo erectus/ergaster. Walking upright required anatomical changes that influenced their diet and social behavior, while the larger brain necessitated by a harsher climate promoted advanced tool use.
Step-by-step explanation:
The anatomy and behavior of Homo erectus/ergaster and its adaptations to savannah life are crucial to understanding their evolution. The savanna hypothesis suggests that various human traits, including upright bipedalism, evolved as adaptations to a savanna habitat. With the emergence of Homo erectus roughly two million years ago, we observed significant changes such as increased meat-eating, a more energy-efficient gait for long-distance walking and running, and the necessity for advanced cognitive abilities to make and use tools for better survival.
As Homo erectus began to walk upright, changes in their anatomy occurred - one being the movement of digestive organs lower into a smaller space, prompting a shift in diet towards more easily digestible foods like nuts, fruits, and meats. This also coincided with encephalization, or the growth of the brain, which was metabolically expensive and required high-quality food to sustain. Consequently, their hands were freed up to use tools, which likely led to advances in manual dexterity and tool sophistication. The use of fire for warmth and cooking and the potential development of rudimentary vocal communication would have aided in the species' social cooperation and survival.
A significant outcome of the digestive organ rearrangement was the species' dietary change from tough plant materials to nutrient-rich foods, thereby supporting a smaller digestive system compatible with the increased caloric demand of a larger brain. The expensive tissue hypothesis further supports this concept, indicating that the energy previously used for maintaining a large digestive tract was reallocated to brain development.