Middle Genus Homo (Muddle in the Middle)

He knows a lot about the science stuff, Professor Dave explains. We have already introduced the earliest species of the genus Homo, but there are several more to cover before we reach modern humans. The middle Pleistocene is colloquially known as the muddle-in-the-middle due to the fact that numerous Homo species are known from this period, but their relationships to one another are somewhat mysterious. This is due in part to the number of proposed species and the fact that many of them were interbreeding. Homo ergaster or African Homo erectus is thought to have given rise to the last common ancestor of Homo sapiens, Neanderthals, and Denisovans, all of whom we will meet a bit later. However, who this ancestor was is up for debate. Proposed hominin species that link these groups include Homo heidelbergensis, Homo rhodesiensis, Homo antecessor, and Homo bodoensis. Traditionally, this role has been assigned to Homo heidelbergensis. Homo heidelbergensis is one of the most controversial hominins for many reasons. The type specimen is a mandible, and the characteristics defining the species are not uniquely derived, but rather perceived to be transitional between Homo sapiens and earlier Homo erectus. Much like Homo erectus, this hominin has a sensu stricto and sensu lato definition, with the former encompassing the European specimens and the latter including African and Asian specimens. For this reason, Homo heidelbergensis is generally appreciated to be ancestral to Homo neanderthalensis, the Neanderthals, who evolved entirely in Europe. This is due to some characteristics that link the two species, effectively to the exclusion of Homo sapiens. As a result, some have proposed that the African Homo heidelbergensis should instead be known as Homo rhodesiensis. This is also controversial, both scientifically and culturally. From a scientific standpoint, some have argued that Homo heidelbergensis should simply be subsumed into the Neanderthals. This would make Homo neanderthalensis a much more variable and long-lived species, and it follows then that early Homo sapiens, or Homo rhodesiensis, should also be subsumed into that species. However, work from the 2010s suggests that a partial skull from Ethiopia links traditional Homo heidelbergensis to Homo ergaster directly. If this is the case, then Homo heidelbergensis originates in Africa, as most hominins do. This skull lacks any of the classically Neanderthal characteristics, but can be tied morphologically to some of the later Heidelbergensis neanderthalensis material. One can quickly see how this gets rather complicated. The Homo sapiens version of Homo heidelbergensis, Homo rhodesiensis, is not much better. Culturally, Homo rhodesiensis has deep colonial roots, being named after British imperialist and diamond magnate, Cecil Rhodes. This is where Homo bodoensis comes in. In 2021, Roxandic and colleagues proposed that all of Homo rhodesiensis should be renamed Homo bodoensis, after the Bodo skull. As well meaning as this was, it did not resolve the phylogeny issues presented by the material attributed to Homo heidelbergensis and Homo rhodesiensis. The problem is further complicated by another hominin known as Homo antecessor. While most material from Homo heidelbergensis and Homo rhodesiensis are younger than one million years, Homo antecessor can be dated as old as 1.2 million years. It was found in Spain and originally shook things up due to the proposal that its face was remarkably derived. This made it a good candidate for the last common ancestor of humans and Neanderthals, booting Homo heidelbergensis aside for the time being. The face is extremely flat, and the jaw is considered to be quite grassled. The vertebral column and limbs are very much like modern humans as well, and the technology found at the sites are par for the course. However, genetic work may have ousted this hominin from our lineage to an offshoot. Proteins collected from one of the teeth appear to remove it from the human line. However, paleoanthropologists have pointed out that the morphology additionally prevents a throughline. While the details of how each of these potential species are connected are hazy, there is no doubt that the series of individual specimens we have span the morphologic difference between earlier hominins and the three big contenders of the late Pleistocene. Let's now continue to move forward within the genus Homo.