Saturday, 30 October 2021

Evolution News - A Newly-Named Species of Archaic Hominin Clarifies our Evolutionary Picture

Artist's rendering of Homo bodoensis
Credit: Ettore Mazza
Experts name new species of human ancestor | University of Winnipeg News

Far from there being no transitional fossils showing the evolution of modern humans from archaic ancestors, as Creationists traditionally claim, there are so many of them that they tend to confuse rather than clarify the picture

Fossils are, of course, an irregular and infrequent snapshot of an evolving species over time, so palaeontologists always have a problem of slotting a new species into existing classifications because there is never a sharp delineation between an ancestral form and a descendant one. It's a bit like trying to determine exactly where one colour changes to another in a rainbow.

Where does the colour change?

So, the tendency has been to name a new find which is significantly different to any others, as a new species, with a name often derived from the place where they were discovered - the scientific equivalent of naming it 'Heidelberg Man' or 'Rhodesia Man'. This is even more problematic if the species is widespread and subject to regional variation, consequently, definitions can be fuzzy and confusing as newer finds are slotted into pre-existing types, each new type broadening and blurring the definition of that species.

Talking about human evolution during this time period became impossible due to the lack of proper terminology that acknowledges human geographic variation.

Naming a new species is a big deal, as the International Commission on Zoological Nomenclature allows name changes only under very strictly defined rules.

Dr Mirjana Roksandic, co-first author
Winnipeg University, Winnipeg, Manitoba, Canada
This international team led by Dr. Mirjana Roksandic from Winnipeg University, Canada has clarified and simplified this muddle in the middle based on latest research and DNA analysis where DNA has been recovered and analysed. They looked especially at specimens that had been classified as Homo heidelbergensis or H. rhodesiensis, both of which carried multiple, often contradictory definitions. European specimens previously classified as H. heidelbergensis have been shown by DNA analysis to be early H. neanderthalensis, while H. rhodesiensis, named when Zimbabwe was still a British colony called Southern Rhodesia, has a name which is too closely associated with Cecil Rhodes and some of the more despicable and brutal aspects of Britain's former imperialism in Africa.

As the Winnipeg University news release explains:
The Middle Pleistocene (now renamed Chibanian and dated to 774,000-129,000 years ago) is important because it saw the rise of our own species (Homo sapiens) in Africa, our closest relatives, and the Neanderthals (Homo neanderthalensis) in Europe.

However, human evolution during this age is poorly understood, a problem which paleoanthropologists call 'the muddle in the middle" The announcement of Homo bodoensis hopes to bring some clarity to this puzzling, but important chapter in human evolution.

The new name is based on a reassessment of existing fossils from Africa and Eurasia from this time period. Traditionally, these fossils have been variably assigned to either Homo heidelbergensis or Homo rhodesiensis, both of which carried multiple, often contradictory definitions.


Recently, DNA evidence has shown that some fossils in Europe called H. heidelbergensis were actually early Neanderthals, making the name redundant For the same reason, the name needs to be abandoned when describing fossil humans from east Asia according to co-author, Xiu-Jie Wu (Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China).

Further muddling the narrative, African fossils dated to this period have been called at times both H. heidelbergensis and H. rhodesiensis. H. rhodesiensis is poorly defined and the name has never been widely accepted. This is partly due to its association with Cecil Rhodes and the horrendous crimes carried out during colonial rule in Africa — an unacceptable honour in light of the important work being done toward decolonizing science.

Homo bodoensis, a new species of human ancestor, lived in Africa during the Middle Pleistocene.
Image Credit: Ettore Mazza

The name "bodoensis" derives from a skull found in Bodo D'ar, Ethiopia, and the new species is understood to be a direct human ancestor. Under the new classification, H. bodoensis will describe most Middle Pleistocene humans from Africa and some from Southeast Europe, while many from the latter continent will be reclassified as Neanderthals.

The co-first author, Predrag Radovit (Faculty of Philosophy, University of Belgrade, Serbia) says, "Terms need to be clear in science, to facilitate communication. They should not be treated as absolute when they contradict the fossil record."

The introduction of H. bodoensis is aimed at "cutting the Gordian knot and allowing us to communicate clearly about this important period in human evolution" according to one of the co-authors Christopher Bae (Department of Anthropology University of Hawai'i at Manoa).
A simplified model for the evolution of the genus Homo over the last 2 million years, with Homo bodoensis sp. nov. positioned as the ancestral (mostly African) form of Homo sapiens
The team's findings and recommendations are published open access in the online journal, Evolutionary Anthropology. This paper contains a very interesting discussion of the history of 'H. heidelbergensis' and the role it played in the origins of this muddle. In their abstract, the authors say:

Recent developments in the field of palaeoanthropology necessitate the suppression of two hominin taxa and the introduction of a new species of hominins to help resolve the current nebulous state of Middle Pleistocene (Chibanian) hominin taxonomy. In particular, the poorly defined and variably understood hominin taxa Homo heidelbergensis (both sensu stricto and sensu lato) and Homo rhodesiensis need to be abandoned as they fail to reflect the full range of hominin variability in the Middle Pleistocene. Instead, we propose: (1) introduction of a new taxon, Homo bodoensis sp. nov., as an early Middle Pleistocene ancestor of the Homo sapiens lineage, with a pan-African distribution that extends into the eastern Mediterranean (Southeast Europe and the Levant); (2) that many of the fossils from Western Europe (e.g. Sima de los Huesos) currently assigned to H. heidelbergensis s.s, be reassigned to Homo neanderthalensis to reflect the early appearance of Neanderthal derived traits in the Middle Pleistocene in the region; and (3) that the Middle Pleistocene Asian fossils, particularly from China, likely represent a different lineage altogether.

This is a great example of how science adopts a provisional interpretation of the data until there is enough available to replace it with a better explanation. Instead of a myriad different species of hominins in Africa, leading to a confusing picture of human evolution, with no clear pathway through the muddle, we now have a single, geographically variable species from which H. sapiens emerged, just as we would expect of a geographically widespread species. The new name for this species means we have a simplified progression from a pan-African most recent common ancestor (MRCA) to H. sapiens, with all the regional variation being subsumed into that single species with a range extending up into the Eastern Mediterranean and the Levant and no sharp delineations needed to establish when one species emerged from its ancestral form.

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