Final answer:
Multiregional theorists suggest that cultural improvements in toolmaking, subsistence patterns, and symbolic expression are responsible for gradual changes in human facial features, teeth, and jaws as Homo sapiens evolved. These cultural developments, accompanied by environmental factors and changes in diet, influenced our physical and cerebral evolution.
Step-by-step explanation:
To explain why human evolution would proceed gradually and in the same direction in various parts of the Old World, multiregional theorists point to cultural improvements in toolmaking, subsistence patterns, and symbolic expression as driving factors that could cause the changes seen in the face, teeth, and jaws as Homo sapiens emerged. During the last 800,000 years, there has been a trend towards smaller faces, jaws, and front teeth, but much larger brains in Homo sapiens compared to earlier Homo species. Additionally, technological advancements related to toolmaking spread globally as human populations migrated. The adoption of new technologies likely affected dietary habits and thereby influenced the physical evolution of humans. About 40,000 years ago, there was a notable change in these practices, indicative of a cultural evolution comparable in its transformative impact to the Industrial Revolution. This was in parallel with the ability of humans to develop and use symbolic language, which also had implications on brain development. The intersection of climatic changes, migration patterns, and cultural evolution played a significant role in shaping human biology. Environmental factors compelled adaptive changes and sparked the development of new skill sets that characterized our species, contributing to our resilience and survival.