A research paper published in 2025 (Candidate Denisovan fossils identified through gene regulatory phenotyping, by Nadav Mishol, Gadi Herzlinger, Yoel Rak, Uzy Smilanksy, Liran Carmel, David Gokhman, bioRxiv 2024.04.18.590145; doi: https://doi.org/10.1101/2024.04.18.590145 and in Proceedings of the National Academy of Sciences doi: 10.1073/pnas.2513968122) reported the study of the shape of different skulls from the Middle Pleistocene, spanning Eurasian and African specimens, including Neanderthal, Homo erectus and modern humans to try to identify the traits that indicate the Denisovan morphology. The study found something quite interesting besides the similarity between Denisovans and some East Asian fossils, below I cite their conclusions and highlight the relevant part:
"these analyses revealed that the East Asian specimens of Harbin and Dali show an exceptionally high concordance with the Denisovan profile, surpassing all other examined Middle Pleistocene hominin specimens, including Neanderthals. Specifically, 15 out of 18 of Dali’s features and 16 out of 18 of Harbin’s matched Denisovan predictions. These findings are robust to overall skull size and to correlations between phenotypes. We also found that Kabwe 1 shows a strong affinity to the Denisovan–Neanderthal clade and might be placed near its root"
Kabwe the African fossil
Kabwe 1 was unearthed in 1921 in Kabwe, in what is now Zambia. It is a fossil skull also known as the Rhodesia man or Broken Hill, and has been classified as a member of the Homo heidelbergensis group. It is rather primitive, with heavy brow ridges, and a flat forehead, its shape resembles that of Homo erectus yet it is relatively recent, dated to around 324,000 - 274,000 years old (source) which makes it contemporaneous with the first members of our species, Homo sapiens who are said to have appeared in North Africa 300,000 years ago.
Besides the oddity of archaic and moderns co-existing in Africa 300 kya. Kabwe 1 is extremely close to Denisovans! Which is an unusual finding because Denisovans are not known to have migrated into Africa, they are better known as East or Southeast, or Central Asian populations that admixed over there with modern humans as these entered that region around 50 ky ago.
Let's see what the paper has to say about this similarity:
"Several test subjects, most notably Kabwe 1, exhibit unexpectedly high concordance with the Denisovan profile, despite being unlikely to be Denisovans. Although discovered in Africa, Kabwe 1 not only aligns well with the Denisovan profile (Fig. 4) but also clusters closely in the PCA with Dali, a potential Denisovan (Fig. 6 and SI Appendix, Fig. S3). Although our current knowledge of Denisovan habitat is lacking, it is unlikely that they reached Southern Africa. Hence, Kabwe 1 is unlikely to be directly positioned on the Denisovan lineage. A more plausible explanation is that the resemblance of some of these specimens to Denisovans reflects a proximal phylogenetic affinity with the Neanderthal–Denisovan clade, perhaps close to its root."
So, the authors assume that there has been no migration of Denisovans into Africa, and based on this assumption they suggest that the African fossil is similar to Denisovans because it was a close relative to the Denisovan-Neanderthal group that left Africa, and split into Neanderthals and Denisovans. A conclusion repeated again in the closing part of the paper, as you can read below:
"The resemblance of several specimens attributed to H. heidelbergensis to the Denisovan profile, and specifically the African specimen Kabwe 1, is particularly intriguing. The similarity between Kabwe 1 and other high-scoring specimens is evident in all PCAs (Figure 4 and Supplementary Figure 10), suggesting that this resemblance is not limited to Denisovan-like phenotypes. Despite our limited knowledge of the true range of Denisovans, it is unlikely that they reached Southern Africa, hence Kabwe 1 is unlikely to be directly positioned on the Denisovan lineage. A more plausible explanation is that the resemblance of some of these specimens to Denisovans reflects a proximal phylogenetic affinity with Denisovans. For example, H. heidelbergensis specimens were positioned either close to the split between modern and archaic humans or close to the split between Neanderthals and Denisovans [29]. If H. heidelbergensis is indeed phylogenetically closer to the Neanderthal-Denisovan split than Neanderthals are, it is expected to exhibit an even greater similarity to the Denisovan profile than Neanderthals do. Another alternative explanation is that Denisovans might have retained several ancestral phenotypes observed in H. heidelbergensis [59], or that these phenotypes were affected by gene flow into Denisovans, originating from contemporaneous H. heidelbergensis [17]."
The authors don't explain how the African fossil can be closer to the Denisovans than the Neanderthals. It is assumed that neither group entered Africa. That the common ancestor of Denisovans and Neanderthals left Africa, splitting from the group that would lead to us, modern humans. Then, in Eurasia, the ancestral group of Denisovans and Neanderthals split into two species, one heading East, the other colonizing the West of Eurasia. So, how could a primitive hominin in Zambia be closer to a group that split in the Levant?
The second explanation requires explaining why the Denisovans ended up with the primitive ancestral form found in Kabwe but not the Neanderthals. The final explanation of gene flow into Denisovans via contemporaneous Homo heidelbergensis would require them being alive and kicking in Western Eurasia around 600 ky ago!
The nice part of this paper is that it is thought provoking: Denisovans and Homo heidelbergensis are linked. Notice that Heidelbergensis got its name from a site in Heidelberg, Germany where it was found in 1908 (source). It is found in Europe and Africa. Of course, it is claimed to have evolved in Africa. But, could these people have evolved in Eurasia, leading to the ancestor of modern humans, Denisovans and Neanderthals, adding more genes to the Denisovans who carried them east, and finally, a group of heidelbergensis moved into Africa resulting in the Zambia fossils?
The current bias against an Into Africa flow makes this hypothesis unlikely to be accepted. But it seems the most logical one. Furthermore, flow of the heidelbergensis into Atapuerca people and then from Spain into North Africa seems a plausible explanation for the evolution of Modern Humans separately from the Neanderthal-Denisovan group.
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