What is the evolutionary relationship among fossils that share many similarities, but also subtle differences, separated across time and space?
What is the evolutionary relationship among fossils that share many similarities, but also subtle differences, separated across time and space? This question, prompted by the early Chinese and Javan fossils, remains an active research question today for the much larger sample of fossils assigned to H. erectus. Whether or not a sample from one region, for example Africa, part of a polytypic, geographically widespread lineage ( Homo erectus), or whether it is part of a related, but different species, is a debated topic and reveals much about the evolutionary pattern of the species (Rightmire 1998). For example, some researchers argue that H. erectus is restricted largely to Eastern and Southeast Asia, consistent with the original fossils attributed to the taxon. In that case, the bulk of its representatives lived from the end of the Lower Pleistocene through the Middle Pleistocene (~1.4-0.2 mya). From this perspective, earlier fossils from Western Asia (e.g., Dmanisi, Georgia; Figure 2) and Africa (e.g., Koobi Fora, Kenya) that are similar to the classic Asian H. erectus, but also have more ancestral traits, might be considered a separate lineage (often called Homo ergaster). Middle Pleistocene remains from Europe might be a second or third separate lineage ( Homo heidelbergensis). In this view, the ecological niche occupied by these species is more limited, leading to the isolation, and ultimately speciation, among different regional populations.