Human life history is characterized by an extended period of immaturity during which there is a disjunction between cerebral and somatic growth rates¹. This mode of ontogeny is thought to be essential for the acquisition of advanced cognitive capabilities in a socially complex environment while the brain is still growing². Key information about when and how this pattern evolved can be gleaned from the teeth of fossil hominins because dental development informs about the pace of life history^3,4,5. Here we show that the first evolutionary steps towards an extended growth phase occurred in the genus Homo at least 1.77 million years ago, before any substantial increase in brain size. We used synchrotron phase-contrast tomography⁶ to track the microstructural development of the dentition of a subadult early Homo individual from Dmanisi, Georgia. The individual died at the age of 11.4 ± 0.6 years, shortly before reaching dental maturity. Tooth growth rates were high, similar to rates in living great apes. However, the Dmanisi individual showed a human-like delayed formation of the posterior relative to the anterior dentition, and a late growth spurt of the dentition as a whole. The unique combination of great-ape-like and human-like features of dental ontogeny suggests that early Homo had evolved an extended growth phase before a general slow-down in life history, possibly related to biocultural reproduction⁷ rather than brain growth.

人类生活史的特点是长时间的不成熟，在此期间，大脑和躯体生长速度之间存在脱节¹。这种个体发育模式被认为对于在大脑仍在生长的社会复杂环境中获得高级认知能力至关重要²。可以从古人类化石的牙齿中收集到有关这种模式何时以及如何进化的关键信息，因为牙齿发育决定了生活史的速度^3,4,5。在这里，我们表明，迈向延长生长期的第一个进化步骤发生在至少 177 万年前的 Homo 属，当时大脑大小还没有大幅增加。我们使用同步加速器相差断层扫描⁶ 来跟踪来自佐治亚州德马尼西的亚成年早期人个体的牙列的微观结构发育。该个体在 11.4 岁± 0.6 岁时死亡，就在牙齿成熟前不久。牙齿生长速度很高，与现存类人猿的生长速度相似。然而，Dmanisi 个体表现出相对于前牙列的后部类似人类的延迟形成，并且整个牙列的生长突增较晚。牙齿个体发育的类大猿和类人特征的独特组合表明，早期人在生活史普遍放缓之前已经进化出一个延长的生长阶段，这可能与生物文化繁殖⁷ 而不是大脑生长有关。