Institute of Human Origins, and School of Human Evolution and Social Change, Arizona State University, Tempe, AZ, 85287, USA; Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, D.C., USA; Department of Human Evolutionary Biology, Harvard University, Cambridge, MA, 02138, USA.
Institute of Human Origins, and School of Human Evolution and Social Change, Arizona State University, Tempe, AZ, 85287, USA.
J Hum Evol. 2020 Aug;145:102823. doi: 10.1016/j.jhevol.2020.102823. Epub 2020 Jul 8.
Age at lower first molar (M) emergence is a commonly used proxy for inferring life-history scheduling in fossil primates, but its utility is dependent on knowing to what extent extant populations vary in this datum and how this variation correlates with the scheduling of life-history variables. Here, we address the first of these issues among extant chimpanzees. While age at M emergence has been documented in several live individuals from the Kanyawara population of Pan troglodytes schweinfurthii in Uganda, it has been estimated for only one individual of Pan troglodytes verus, based on a deceased animal from the Taï Forest in Côte d'Ivoire. To further explore interpopulation variation in this variable in chimpanzees, and using dental histology, we calculated ages at death for two wild-shot individuals of P. t. verus with erupting M, both collected in Liberia during the mid-1950s, and estimated ages at M emergence from the ages at death. The overall range for these two individuals is ∼4.2-4.6 yr, compared with an age of ∼3.7 yr for the individual from the Taï Forest, and <2.5-3.3 yr for the several individuals of P. t. schweinfurthii. While the absolute range of ∼2 yr in these samples combined is little greater than in captive chimpanzees, the disparity between the samples of P. t. schweinfurthii and P. t. verus is striking, although it cannot be determined if this disparity represents a subspecies difference or simply population differences expressed in two different subspecies. While life-history data are unavailable for the population to which the Liberian chimpanzees belonged, the difference in M emergence ages between these individuals and those from Kanyawara still suggests caution when attempting even broad life-history inference in fossil apes and hominins based on age at M emergence.
下第一磨牙（M）萌出的年龄是推断化石灵长类动物生活史策略的常用指标，但该指标的有效性取决于了解现生物种在该数据上的变化程度以及这种变化与生活史变量的安排之间的相关性。在这里，我们研究了现生物种中的第一个问题。虽然乌干达的卡尼亚瓦拉群体中的几个活体黑猩猩的 M 萌出年龄已经有记录，但仅根据科特迪瓦泰森林中一只死亡的黑猩猩 Verus 个体估计了 M 萌出年龄。为了进一步探讨黑猩猩在这个变量上的种群间变异，并使用牙组织学，我们计算了两个野生 M 萌出的 P. t. verus 个体的死亡年龄，这两个个体都于 20 世纪 50 年代中期在利比里亚采集，并且根据死亡年龄估计了 M 萌出年龄。这两个个体的年龄范围约为 4.2-4.6 岁，而泰森林个体的年龄约为 3.7 岁，而 P. t. schweinfurthii 的几个个体的年龄小于 2.5-3.3 岁。虽然这两个样本的绝对范围约为 2 岁，但与 P. t. schweinfurthii 样本的差异是惊人的，尽管尚不能确定这种差异是否代表亚种差异或仅仅是两个不同亚种中表达的种群差异。虽然无法获得这些黑猩猩所属种群的生活史数据，但这些个体与 Kanyawara 个体的 M 萌出年龄差异表明，即使根据 M 萌出年龄尝试进行广泛的化石猿和人类的生活史推断，也需要谨慎。
