Which theory of the selection pressures and environmental features the were key factors in hominin evolution is best supported by the fossil and geological evidence? 关于人类进化过程中选择压力和环境特征的关键因素，哪种理论最能得到化石和地质证据的支持？单项选择题

Rapid environmental change selected greater cognitive capacity for adaption and for larger and more complex social structures. 快速的环境变化促使人们进化出更强的认知能力来适应环境，并构建更大、更复杂的社会结构。

The migration out of Africa was only accomplished by hominins with vastly increased brain size compared to those who distributions are restricted to Africa. 只有脑容量远大于分布于非洲的人类才能走出非洲。

Life on the plains (rather than in forests or jungles) selected bipedalism and larger social groups, which coincides with selection for bigger brains. 平原上的生活（而不是森林或丛林中的生活）促使了双足行走和更大的社会群体的出现，这与大脑容量增大的选择相吻合。

Bigger brains were selected once bipedalism freed the hands (to make tools and sign communication.) 双足行走解放了双手（用于制造工具和进行符号交流），从而促使大脑体积增大。