Which hypothesis was proposed by Smith and Jones in the early 1900s?

The arboreal hypothesis, proposed by Smith and Jones in the early 1900s, suggests that the characteristics of primates—such as grasping hands and forward-facing eyes—evolved primarily because these traits provided advantages for living in trees. This hypothesis argues that the adaptations seen in primates are responses to the challenges of an arboreal lifestyle, including the need for better vision to navigate through branches and enhanced dexterity for grasping and manipulating objects.

In the context of primate evolution, this hypothesis emphasizes the importance of a tree-dwelling environment in shaping the physical and sensory traits of these species. Such adaptations improved their ability to forage for food, escape from predators, and move effectively through their habitats, which were predominantly arboreal.

While the other hypotheses touch on interesting aspects of primate evolution—like the visual predation hypothesis that focuses on foraging behavior and the angiosperm radiation hypothesis linking primate evolution with the rise of flowering plants—the foundational concept of the arboreal hypothesis directly aligns with the specific proposals made by Smith and Jones during that period of research, making it the correct answer.