从灵长类动物到直立人种，人类缘何得以进化？原因可能很复杂。美国研究人员6月4日报告说，大约350万年前原始人类开始“吃草”，饮食习惯的变化可能是人类进化过程中的重要一步。
美国科罗拉多大学等机构的研究人员4日在美国《国家科学院学报》报告说，他们利用碳同位素技术，对来自东非的原始人类和狒狒等灵长类动物的牙釉质化石样本进行了分析。结果发现，大约350万年前，原始人类的饮食结构发生了变化，食用热带草和莎草明显增加。
科罗拉多大学教授马特·施蓬海默说，400万年前，原始人类的饮食结构还和猩猩类似，主要以果实和一些叶片为食；大约350万年前，一些原始人类确实开始食用热带草和莎草等新食物。
不过，研究人员表示，碳同位素技术无法确定原始人类食用热带草或莎草的具体部分，原始人类究竟食用这些植物的种子、枝叶或是根茎还不知晓。
研究人员指出，原始人类开始吃草，可能标志着他们与猩猩等其他灵长类动物的脱离。研究人员说：“长期以来饮食是人类进化的一种驱动力，饮食变化关联着脑容量变大和直立行走的出现。”(生物谷Bioon.com)
doi: 10.1200/JOP.2012.000811
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Diet of Australopithecus afarensis from the Pliocene Hadar Formation, Ethiopia
Jonathan G. Wynna,1,Matt Sponheimerb,William H. Kimbelc,Zeresenay Alemsegedd,Kaye Reedc,Zelalem K. Bedasoe, andJessica N. Wilsona
The enhanced dietary flexibility of early hominins to include consumption of C4/crassulacean acid metabolism (CAM) foods (i.e., foods derived from grasses, sedges, and succulents common in tropical savannas and deserts) likely represents a significant ecological and behavioral distinction from both extant great apes and the last common ancestor that we shared with great apes. Here, we use stable carbon isotopic data from 20 samples of Australopithecus afarensis from Hadar and Dikika, Ethiopia (>3.4–2.9 Ma) to show that this species consumed a diet with significant C4/CAM foods, differing from its putative ancestor Au. anamensis. Furthermore, there is no temporal trend in the amount of C4/CAM food consumption over the age of the samples analyzed, and the amount of C4/CAM food intake was highly variable, even within a single narrow stratigraphic interval. As such, Au. afarensis was a key participant in the C4/CAM dietary expansion by early australopiths of the middle Pliocene. The middle Pliocene expansion of the eastern African australopith diet to include savanna-based foods represents a shift to use of plant food resources that were already abundant in hominin environments for at least 1 million y and sets the stage for dietary differentiation and niche specialization by subsequent hominin taxa.
