Final answer:
The main problem with Savanna theories for the origins of bipedalism is that they are not testable, making it challenging to understand why our ancestors evolved bipedalism. Multiple hypotheses have been proposed, making it difficult to determine the main driving factor behind bipedalism.
Step-by-step explanation:
The main problem with Savanna theories for the origins of bipedalism is that they are not testable. This means that scientists cannot directly observe or experimentally validate these theories. Without testable hypotheses, it becomes challenging to understand why our ancestors evolved the behavior of bipedalism. Additionally, there have been multiple hypotheses proposed, ranging from carrying tools or food to increasing energy efficiency, making it difficult to determine the main driving factor behind bipedalism.