Part 4 of this series concluded that the genus Homo (“human-like beings”) is a monophyletic lineage that emerged ca 2.5 million years ago (Mya) from ‘gracile’ African australopithecines close to Australopithecus africanus – see Part 3. The earliest broadly accepted Homo – “handy man” habilis (probably including bigger-brained ‘rudolfensis’) – was (like australopiths) pygmy-sized, fully-furred, sexually size-dimorphic and long-armed. However, like Homo, it had a much larger brain; its face was less prognathic; its brow-ridge was less prominent; its cheek bone was more rounded; it had a smaller jaw harboring smaller teeth (especially canines and molars) arranged in a parabola- (not U-) shaped arch, and it was a proficient – but not expert, obligate – biped who made and used tools.
Cladistically (evolutionarily genealogically), habilis is the sister species of a taxonomically highly polytypic, evolutionarily reticulate (bush-like) Homo sapiens sensu lato that diverged at ca 2 Mya. This developmentally plastic ‘super-sapiens’ includes the palaeo-subspecies ‘ergaster‘ (African erectus), ‘true’ erectus (Eurasia) and, subsequently, European neanderthalensis and Asian ‘denisova’ (both derived from Eurasian erectus) and the extant African sapiens sensu stricto (derived from African erectus). These forms of Homo were/are: later-maturing, longer-lived, ‘naked’, sweaty, tall, relatively sexually monomorphic, larger-brained, shorter-armed ‘flat-faced’; and big-nosed, and were efficient, obligate bipeds capable of long-distance dispersal.
And disperse, diverge, hyper-wander and actively interbreed they did! Forms of early erectus occupied (and diverged within) much of Africa, Europe (west to England and Spain) and Asia (east to Java) by 1.6 Mya, and eastern China and south-eastern Asia by ca 780 Kya. Super-sapiens had given rise to Neanderthals, Denisovans and Archaic African sapiens by 350 Kya.
These forms of Homo are, at most, geographical ‘real races’ (subspecies) because their covarying ‘diagnostic’ morphological differences seem to have evolved during periods of isolation in habitat ‘islands’ and are mosaics of primitive and derived features that are largely quantitative (rather than autapomorphic – uniquely qualitative species-specific) and non-functional in nature. They are NOT evolutionarily ‘real’ species – sets of populations that are evolutionarily effectively ‘amputated’ from other such sets. Time-and-again they re-connected and admixed genetically and – maybe even culturally – keeping them evolutionarily cohesive amongst themselves and to sapiens. Indeed, genetic admixture between Neanderthals and Denisovans has been widely detected in present-day non-African sapiens sensu stricto, and admixture between modern humans and archaic lineages appears to have been bi-directional. For example, this resulted in the replacement of both the mitochondrial DNA and Y chromosome of Neanderthals with that of early sapiens sensu stricto between ca 370 and 220 Kya, and strong overall genetic similarity (99.7% ) between them.
This pattern of morphological and molecular variation and interbreeding is consistent with what occurs when extant subspecies of African primates and birds come into contact (e.g. Papio baboons and Helmeted Guineafowl Numida meleagris and – see Part 1). In fact, since present-day, non-African, globally distributed modern sapiens retains both genetic and morphological ‘footprints’ from these palaeo-races – some of which may be adaptive – they are still arguably ‘extant’!
Another major concern about the taxonomy and phylogeny of Homo is: Just how far can one ‘push’ morphological fossil evidence in terms of delimiting species and explaining their evolution within a cladistic (tree-like) format.
‘Bits of unsortable bones in museum bins’
Most palaeo-anthropologists currently accept that there has been less-than-mooted anagenetic – ‘chain-of-being’ – evolution from ancestral australopithecine ‘chimp-men’ towards anatomically more ‘competitive’ and destructive anatomically modern humans. Moreover, they maintain that chronologically important, divergent, cladogenic (branch-like) variation within and between “different” forms of archaic and pre-modern Homo was the norm. This has resulted in the erection of dozens of species and subspecies of Homo fossils and – perniciously – races within extant sapiens and depicting their assumed evolutionary genealogy in ‘cladograms’ (evolutionary ‘trees’).
The foremost examples of ‘invented’ vs discovered fossil species of Homo are the more ‘primitive’, ‘gracile’, small-brained, less heavily brow-ridged, more prognathic African ergaster vs the ‘derived’, bigger-brained, heavily browed Eurasian ‘true’ erectus (See Part 4, here and here). In fact, early forms of ergaster/erectus from BOTH Africa and Western Asia/Eastern Europe (e.g. Dmanisi, Georgia – ‘H. georgicus’) are still moderately prognathic and have australopith-like small crania and morphological organization of their brain’s frontal lobe. In short, ergaster/erectus is better subsumed into a single, widespread, chrono-geo-graphically variable palaeo-subspecies – erectus.
‘Closer’ to Homo sapiens sensu stricto are ‘Homo’ antecessor and heidelbergensis. These chrono-species were created to ‘bridge’ the gap – described as the “muddle in the middle “ – between the relatively small-brained and prognathic Homo ergaster/erectus and big-brained and still flatter-faced Homo neanderthalensis and sapiens. These proposed species are temporally bounded taxa derived from a sequential development pattern which involves continuous, quantitative and uniform change (without branching) from an ancestral form that becomes extinct when it is supplanted by a derived form along an unbranching evolutionary lineage. Such segments of lineages are considered as meaningful, separate taxa because the fossil sample assessed across time has a “unique mix” of features deemed to exceed the overall morphological pattern of variation that occurs within closely related living species. For example, eminent palaeo-anthropologists Chris Stringer and Ian Tattersall favour this taxonomic ‘splitting’ strategy for Homo because differences amongst these putative taxa fall “clearly outside the range of Holocene members of the species” and are necessary to “show the complexity” of recent human evolution. To them, antecessor and heidelbergensis have “substantially differing morphologies” that should not be “brushed under the rug”. Two other eminent palaeo-anthropologists, Milford Wolpoff and Alan Thorne support the alternative view that erectus was a highly geographically variable species that exhibit variable/plastic features that indicate a gradual transformation into sapiens without speciation. Indeed, they claim that 17 of the 23 morphological characters that distinguish erectus from habilis are also found in sapiens.
In short, these chronospecies are intermediate, transitional, mosaic forms that don’t even meet the status of extant, clinally-varying subspecies of Helmeted Guineafowl (Numida meleagris – J. van Alphen-Stahl Unpubl. MSc UCT, 2005) and Papio baboons discussed in Part 1.
Moreover, the hominin fossil record during the muddle in the middle is extremely sketchy. Fossils that derive from this period are, in many cases, extremely limited in number, non-randomly distributed age-sex-wise, and spatially and temporally piecemeal and fragmentary. Even multivariate statistical analysis of these ‘species’ fails to demonstrate discrete clusters of individual specimens. Using such a phenetic species concept for these forms is thus an unwise strategy to justify recognition of entities as lineages that warrant taxonomic status (see Part 3 and here, here and here).
Employing a ‘splitting’ strategy for even statistically discernible forms of humanity in particular “has significant implications on how humanity is viewed because studies of race and human evolution are inexorably linked”. Worse still, such speculative taxonomies and phylogenies may aid ‘scientific’ racists who use the resulting pseudo-taxa with questionable evolutionary status and ‘relationships’ to ‘justify’ their malicious narratives.
Due to space limitations, I defer discussion of the taxonomy and phylogenetics of some ‘real’ other forms of Homo to Part 6.