Human newborns are considered altricial compared with other primates because they are relatively underdeveloped at birth. However, in a broader comparative context, other mammals are more altricial than humans. It has been proposed that altricial development evolved secondarily in humans due to obstetrical or metabolic constraints, and in association with increased brain plasticity. To explore this association, we used comparative data from 140 placental mammals to measure how altriciality evolved in humans and other species. We also estimated how changes in brain size and gestation length influenced the timing of neurodevelopment during hominin evolution. Based on our data, humans show the highest evolutionary rate to become more altricial (measured as the proportion of adult brain size at birth) across all placental mammals, but this results primarily from the pronounced postnatal enlargement of brain size rather than neonatal changes. In addition, we show that only a small number of neurodevelopmental events were shifted to the postnatal period during hominin evolution, and that they were primarily related to the myelination of certain brain pathways. These results indicate that the perception of human altriciality is mostly driven by postnatal changes, and they point to a possible association between the timing of myelination and human neuroplasticity.

与其他灵长类动物相比，人类新生儿被认为是晚熟动物，因为它们出生时发育相对欠佳。然而，在更广泛的比较背景下，其他哺乳动物比人类更晚熟。有人提出，由于产科或代谢限制，人类的晚熟发育是继发性进化的，并且与大脑可塑性的增加有关。为了探索这种关联，我们使用了 140 种胎盘哺乳动物的比较数据来衡量人类和其他物种的晚熟性如何进化。我们还估计了大脑大小和妊娠长度的变化如何影响古人类进化过程中神经发育的时间。根据我们的数据，在所有胎盘哺乳动物中，人类表现出最高的晚熟性进化率（以出生时成年大脑大小的比例来衡量），但这主要是由于出生后大脑大小明显增大，而不是新生儿的变化。此外，我们发现，在古人类进化过程中，只有少数神经发育事件转移到出生后时期，并且它们主要与某些大脑通路的髓鞘形成有关。这些结果表明，人类早熟的感知主要是由出生后变化驱动的，并且它们指出髓鞘形成时间与人类神经可塑性之间可能存在关联。