The environment increased complexity required more neural functions to develop in the hominin brains, and the hominins adapted to the complexity by developing a bigger brain with a greater interconnection between its parts. Thus, complex environments drove the growth of the brain. In about two million years during hominin evolution, the brain increased three folds in size, one of the largest and most complex amongst mammals, relative to body size. The size increase has led to anatomical reorganization and complex neuronal interactions in a relatively small skull. At birth, the human brain is only about 20% of its adult size. That facilitates the passage through the birth canal. Therefore, the human brain, especially cortex, develops postnatally in a rich stimulating environment with continuous brain wiring and rewiring and insertion of billions of new neurons. One of the consequence is that in the newborn brain, neuroplasticity is always turned “on” and it remains active throughout life, which gave humans the ability to adapt to complex and often hostile environments, integrate external experiences, solve problems, elaborate abstract ideas and innovative technologies, store a lot of information. Besides, hominins acquired unique abilities as music, language, and intense social cooperation. Overwhelming ecological, social, and cultural challenges have made the human brain so unique. From these events, as well as the molecular genetic changes that took place in those million years, under the pressure of natural selection, derive the distinctive cognitive abilities that have led us to complex social organizations and made our species successful.

中文翻译：

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更大的大脑适应更复杂的环境。


环境的复杂性增加，需要古人类大脑中发育出更多的神经功能，而古人类通过发育出更大的大脑以及各部分之间更紧密的互连来适应复杂性。因此，复杂的环境推动了大脑的发育。在人类进化的大约两百万年里，大脑的大小相对于身体大小增加了三倍，是哺乳动物中最大、最复杂的大脑之一。尺寸的增加导致了相对较小的头骨中的解剖重组和复杂的神经元相互作用。人类出生时的大脑只有成人大小的 20% 左右。这有助于通过产道。因此，人类大脑，尤其是皮质，在出生后在丰富的刺激环境中发育，大脑不断布线、重新布线和插入数十亿个新神经元。结果之一是，在新生儿大脑中，神经可塑性始终处于“开启”状态，并且在整个生命过程中保持活跃，这使人类能够适应复杂且通常是敌对的环境，整合外部经验，解决问题，阐述抽象思想和创新技术，存储大量信息。此外，古人类获得了音乐、语言和强烈的社会合作等独特的能力。压倒性的生态、社会和文化挑战使人类大脑变得如此独特。从这些事件，以及在自然选择的压力下发生的分子遗传变化，衍生出独特的认知能力，这些能力使我们形成了复杂的社会组织，并使我们的物种取得了成功。