A perennial challenge of evolutionary psychology is explaining prosocial traits such as a preference for fairness rather than inequality, compassion towards suffering, and an instinctive ability to coordinate within small teams. Considering recent fossil evidence and a novel logical test, we deem present explanations insufficiently explanatory of the divergence of hominins. In answering this question, we focus on the divergence of hominins from the last common ancestor (LCA) shared with Pan. We consider recent fossil discoveries that indicate the LCA was bipedal, which reduces the cogency of this explanation for hominin development. We also review evolutionary theory that claims to explain how hominins developed into modern humans, however it is found that no mechanism differentiates hominins from other primates. Either the mechanism was available to the last common ancestor (LCA) (with P. troglodytes as its proxy), or because early hominins had insufficient cognition to utilise the mechanism. A novel mechanism, sub-group level selection (sGLS) is hypothesised by triangulating two pieces of data rarely considered by evolutionary biologists. These are behavioural dimorphism of Pan (chimpanzees and bonobos) that remain identifiable in modern humans, and the social behaviour of primate troops in a savannah ecology. We then contend that sGLS supplied an exponential effect which was available to LCA who left the forest, but was not sufficiently available to any other primates. In conclusion, while only indirectly supported by various evidence, sGLS is found to be singularly and persuasively explanatory of human's unique evolutionary story.

进化心理学的一个长期挑战是解释亲社会特征，例如对公平而非不平等的偏好、对苦难的同情以及在小团队中协调的本能能力。考虑到最近的化石证据和新的逻辑测试，我们认为目前的解释不足以解释人类的分歧。在回答这个问题时，我们关注与潘共享的最后一个共同祖先（LCA）的人类差异. 我们考虑最近的化石发现表明 LCA 是双足的，这降低了这种对人类发育的解释的说服力。我们还回顾了声称可以解释人类如何发展成现代人类的进化理论，但发现没有任何机制可以将人类与其他灵长类动物区分开来。要么该机制对最后一个共同祖先 (LCA) 可用（以P. troglodytes作为其代理），要么是因为早期人类没有足够的认知来利用该机制。通过对进化生物学家很少考虑的两条数据进行三角剖分，假设了一种新的机制，亚组水平选择(sGLS)。这些是潘的行为二态性（黑猩猩和倭黑猩猩）在现代人类中仍然可以识别，以及在大草原生态系统中灵长类动物部队的社会行为。然后，我们认为 sGLS 提供了一种指数效应，该效应对离开森林的 LCA 可用，但对任何其他灵长类动物来说都不够可用。总之，虽然只有各种证据间接支持，但 sGLS 被发现是对人类独特进化故事的独特而有说服力的解释。