How can we justify scientifically that the Homo erectus, Homo heidelberensis, Neanderthal, and modern humans are separate species?
The main argument for treating these hominins as separate species is that each differs from the others in terms of skeletal morphology. Some of these morphologies are thought to arise from genetically programmed differences in growth. Thus, morphological differences are treated as proxies for genetic differences. Most of these fossil taxa also have non-overlapping distributions in time and space. This further suggests they were reproductively isolated from each other. This combination of morphogenetic difference and inferred reproductive isolation are basic criteria for identifying a species. Now, you are correct to be skeptical. We do not know the specific genetic underpinnings of many aspects of skeletal growth. Nor are we ever likely to know the precise geographic and chronological range of all hominin species. Treating these hominin morphological taxa as biological species is in essence, accepting a hypothesis that cannot be proven conclusively wrong. What experts should I ask abou
