Why did the chewing complex start to decline in size with H. habilis?

The decline in the chewing complex size with H. habilis can be attributed to the use of stone tools, which significantly reduced the need for powerful chewing and the ripping and shredding of food. As early humans began to utilize tools for processing their food, they could cut, scrape, and otherwise prepare items in ways that made them easier to consume, lessening the reliance on strong jaws and large teeth. This adaptation reflects a shift in dietary practices that came with tool use, allowing for a broader range of foods to be accessed and consumed efficiently without the anatomical adaptations for extensive chewing.

While other factors, such as diet and environmental influences, play a role in the overall evolution of humans, the direct impact of tool use stands out as a key reason for the observed decline in the size of the chewing complex in H. habilis. The use of tools not only facilitated a change in diet but also drove changes in physical characteristics, demonstrating how behavioral adaptations can lead to morphological changes over time.