Final answer:
Fossil evidence such as the Laetoli footprints and skull morphology of early hominins like Australopithecus and Paranthropus robustus indicates adaptions to a changing climate, such as increased bipedalism and dietary changes related to brain size and energy needs. The robust and gracile forms of australopithecines show diverse adaptations to their environment and diet, driven by colder and more variable climates during the Pliocene epoch.
Step-by-step explanation:
The evidence that indicates a dramatic climate change with the evolution of early hominins such as Australopithecus and Paranthropus robustus includes fossil records showing changes in morphology that were adaptations to new environmental conditions. Notable among these is the discovery of the Laetoli footprints by Mary Leakey, which provide clear evidence of bipedalism in Australopithecus afarensis around 3.5 million years ago, signaling changes in habitat and behavior likely driven by climate variation. Additionally, the morphological differences observed in Paranthropus robustus such as larger teeth for grinding hard foods and a sagittal crest for larger jaw muscles suggest adaptations to a tougher, more fibrous diet in response to cooler, more variable climates of the Pliocene epoch.
Fossil evidence supported by tools like the human evolution interactive timeline illustrates correlations between climate change, dietary adaptations, and increases in brain size. These changes are in line with theories like the expensive tissue hypothesis, which suggests that as the hominin brain grew, high-quality, energy-rich diets became necessary, potentially driving the shift to meat consumption. This shift in diet and the associated changes in digestive systems could have been a response to the demands of a larger brain in a colder climate.
Moreover, the robust and gracile forms of australopithecines show varying adaptations to diet and environment. The robust forms, which had adaptations for consuming tough plant materials, represent a branch of hominins that became extinct, while the gracile forms are considered more closely related to the lineage leading to modern humans. These physical divergences indicate a significant effect of climate on hominin evolution.