What is the savanna hypothesis?

Question

BlackTom AI · Accepted Answer

Question context: We are asked to evaluate statements about the savanna hypothesis and determine which option correctly conveys the idea.
Option 1: 'Bipedalism was selectively favored because it helped our ancestors to stay cool in their warm environment.' While thermoregulation can be a consideration, the classic savanna hypothesis emphasizes ecological changes in habitat (open savannas) driving bipedalism, not specifically cooling the body as the primary selective pressure. This option misconstrues the core mechanism by focusing on thermoregulation alone.
Option 2: 'Climate changes around 8-5 mya due to plate tectonics caused landscape changes in Africa from forests to open grasslands (savannas).' This statement aligns with the broad context of the savanna hypothesis: a shift from forested to more open habitats in Africa during that time period, potentially due to climate shifts and tectonic influences. It correctly situates environmental change as a driver for hominin evolution, making it a plausible description of the hypothesis's backdrop.
Option 3: 'Bipedalism evolved in early humans that were monogamous, specifically to allow male human fathers to provision food and resources to human female partners.' This description mixes social behavior (monogamy, provisioning) with a claim about the origin of bipedalism that is not central to the savanna hypothesis. While provisioning theories exist, the savanna hypothesis traditionally emphasizes habitat change and efficiency of bipedal locomotion in open environments rather than a particular mating system driving the trait.
Option 4: 'Bipedalism was selectively favored in our ancestors when savanna grasslands expanded and forests receded.' This option directly ties the emergence and selection for bipedalism to the ecological shift toward savannas (expansion of grasslands and recession of forests), which is the core idea of the savanna hypothesis. It succinctly captures the proposed adaptive context: moving upright to navigate open habitats and exploit resources efficiently in a savanna environment.

In summary, Option 1 misattributes the primary selective pressure, Option 3 ties the trait to a social-provisioning narrative rather than habitat change, Option 2 describes a credible environmental backdrop but does not explicitly connect it to the functional advantage of bipedalism in the savanna context as clearly as Option 4 does, and Option 4 encapsulates the central claim of the savanna hypothesis by linking bipedalism to savanna expansion and forest recession. The reasoning across options highlights why each is plausible or not within the established framing of the savanna hypothesis.

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