Did Chinese Homo erectus survive into the Late Pleistocene?

14,000-year-old hominin thigh bone has archaic affinities.

In 2012, human remains differing from the modern condition were reported from two sites 300 km (185 miles) apart in southwest China: Longlin Cave in Guangxi Province, and Maludong (‘Red Deer Cave’) in Yunnan Province. The Longlin remains have been radiocarbon dated to 11,500 years old, and those from Maludong to 14,000 years old. The Longlin remains included a partial skull, a temporal bone fragment probably belonging to the skull, a partial lower jawbone and some fragmentary postcranial bones. The cheek bones of the skull are broad and flared sideways; the browridges conspicuous; the chin less prominent than in Homo sapiens; and the remains are very robust. The Maludong remains include a skullcap, two partial jawbones and a partial thighbone.

Popularly reported as the Red Deer Cave people, the hominins were at first thought to represent a single population, but newly-published work suggests that the Longlin skull has affinities to early modern humans. The bony labyrinth (the bony outer wall of the inner ear) of the temporal bone fragment is modern in appearance and it is possible that the skull’s unusual shape might be the result of interbreeding between archaic and modern humans. It has been suggested that Longlin was located in a ‘hybrid zone’ – a border between relict archaic and modern populations. Similar hybrid zones occur with some non-human primate populations.

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The Maludong thighbone is now claimed to show affinities to archaic humans, in particular those from the Early Pleistocene. There is a scarcity of later archaic human remains in East Asia, and the authors of the new report are reluctant to assign the thighbone to a particular archaic human species. However, the likeliest possibility is that the thighbone represents a late survival of Homo erectus in China. Regardless of species, the implications of these new findings is that isolated populations of archaic humans were still in existence in China as late as 11,500 years ago and that some of these populations were interbreeding with modern humans.

References:

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1.  Curnoe, D. et al., Human Remains from the Pleistocene-Holocene Transition of Southwest China Suggest a Complex Evolutionary History for East Asians. PLoS One 7 (3) (2012).

2.  Curnoe, D., Ji, X., Taçon, P. & Yaozheng, G., Possible Signatures of Hominin Hybridization from the Early Holocene of Southwest China. Scientific Reports 5, 12408 (2015).

3.  Curnoe, D. et al., A Hominin Femur with Archaic Affinities from the Late Pleistocene of Southwest China. PLoS One (2015).

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Hitherto-unknown early human species discovered deep inside Rising Star Cave, South Africa

A team led by Lee Burger has announced the discovery of a new species of early human.

Professor Berger, an American palaeoanthropologist working at the University of the Witwatersrand, Johannesburg, is known for Australopithecus sediba, announced in 2010 and at the time was the first new hominin species to be discovered in South Africa for decades. The discovery was when Matthew, Lee’s nine-year-old son, discovered a hominin collar bone embedded in a rock at Malapa, part of a now-eroded cave system near to Sterkfontein and Swartkrans, where many important hominin finds have been made.

Berger felt other cave systems in South Africa had the potential to yield hominin fossils, so in 2013 he recruited a team of cavers to search the Rising Star cave system, 50 km (30 miles) northwest of Johannesburg. The cave has been well explored over the years, but the team came across a narrow 18 cm (7 in.)-wide shaft that dropped vertically for 12 m (39 ft.) into an unexplored chamber. The cavers descended into the chamber and saw a fossil skull and jawbone lying on the floor of the cave. Berger believed that there were hominin fossils and obtained funding from the National Geographic for an expedition.

But to access what became known as Dinaledi Chamber (‘chamber of stars’) was problematic. Before they could even reach the narrow shaft leading down to the chamber, researchers, researchers would have to pass through another tiny shaft known as Superman’s Crawl and then climb a steep section known as Dragon’s Back. Berger placed an advertisement on Facebook for ‘small, skinny’ scientists believing at best there might be three or four people in the world who would fit the criteria. In the event, within days 57 suitable candidates had applied from which he chose six, all women. Within a month, the Rising Star Expedition had set up camp at the cave system and excavations commenced. Working in six-hour shifts, the six women soon recovered more fossil material than had been found in the whole of South Africa in the previous 90 years. Meanwhile, back on the surface, a large team began preparing and cataloguing the fossils, making full use of social media to report progress. A total of 1,550 fossils were recovered, comprising 15 individuals, including males, females and infants.

Berger then invited thirty young postdoctoral researchers from fifteen countries to help him evaluate the haul at a workshop in Johannesburg. They were accompanied by twenty of Berger’s more senior colleagues, who had worked with him on the Australopithecus sediba discovery. This unusual move did not please everybody and some questioned the wisdom of handing over such important fossils to inexperienced researchers.

The findings have now been announced. The remains represent a new human species, Homo naledi, named for the word ‘star’ in the local Sotho language. The new species is comparable in height and weight to a small-bodied modern human or a large australopithecine, with an estimated stature of around 1.5 m (5 ft.) and weighing 40 to 55 kg (88 to 121 lb.). The brain is tiny, ranging from 465 to 560 cc, overlapping entirely with the range of values known for australopithecines. The reconstructed skeleton exhibits both humanlike and apelike features, but in a combination that has not been seen with other hominins. The feet and lower limbs are humanlike, but the upper thighbone, pelvis and shoulders are apelike. The hands and wrists are humanlike, though the fingers are curved suggesting that it spent some of its time in the trees as well as on the ground. Overall, Homo naledi is the most primitive, small-brained hominin ever to have been included in Homo, but the shape of cranium and lower jawbone and the dentition suggest that it is human rather than an australopithecine.

Unfortunately, no dates have yet been published for the fossils. They are presumably too old to be radiocarbon dated, but there is no readily-datable material in the chamber. Calcium carbonate flowstones have been found to have been contaminated with materials from associated muds, making them unsuitable for uranium series dating. All we currently have to go on is the primitive characteristics such as the small brains. These suggest that Homo naledi emerged close to the base of the human family tree 2.5 to 2.8 million years ago. But until we have dates for the fossils, or other fossils turn up that can be dated, it will be difficult to say just where Homo naledi fits into the overall picture of human evolution.

Also troublesome is the question of how the fossils reached Dinaledi Chamber in the first place. There is a near-absence of non-hominin fossils in Dinaledi Chamber – yet these are abundant in the adjacent Dragon’s Back. This rules out the remains having being swept into Dinaledi Chamber by a flash flood, as this would have left a mixture of hominin and non-hominin remains in both chambers. Carnivores are also ruled out: even if there was a carnivore that preyed exclusively on Homo naledi, why would it drag its prey into such an inaccessible location? In any case, none of the bones showed any evidence of having been gnawed by carnivores. Nor does it seem that the hominins fell down a shaft leading into the cave from the surface: there is no evidence that any such shaft had ever existed. The fossils accumulated over time, so it can also be ruled out that a single group entered the chamber for some reason and then become trapped there.

The only obvious explanation is that the remains were deliberately placed in the chamber as part of a post-mortem ritual, although there is no evidence for such rituals until much later. Mass deposition of corpses is first seen at the cave site of Sima de los Huesos in Spain, 430,000 years ago. Even this was nothing more than a hygienic disposal of the corpses rather than any form of ritual. Also, unlike Homo naledi, the brain size of the Sima people was only slightly below that of modern people. In any case, even hygienic disposal seems unlikely as there is no evidence that Rising Star was ever inhabited, and there would surely be no need to use such an inaccessible chamber.

Taken at face value, the evidence from Dinaledi Chamber suggests that early humans were far more behaviourally complex than has long been believed. However, it is probably too soon to jump to conclusions and all that can safely be said is that we don’t yet know how the fossils reached the cavern.

References:

1. Berger, L., Hawks, J., de Ruiter, D. & Churchill, S., 2015. Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa. eLife.

2. Dirks, P. et al., 2015. Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa. eLife.

The LD 350-1 jawbone

Introduction:

A partial lower jawbone and a number of teeth have been recovered from a surface outcrop of fossil-bearing sedimentary rock in the Ledi-Geraru research area, in the Afar region of Ethiopia. This region has long been associated with the fossils of early hominins. The jawbone has been assigned to Homo (species indeterminate) (Villmoare, et al., 2015). The age of the jawbone is constrained by stratigraphic and palaeomagnetic considerations to between 2.80 and 2.75 million years old (DiMaggio, et al., 2015). This means that LD 350-1 is at least 400,000 years older than the earliest previously-known fossil assigned to Homo. The findings are published as two articles in the journal Science.

What was our previous understanding of human origins?

The conventional view is that the first human species was Homo habilis (‘Handy man’). Discovered in 1960 and announced as a new species four years later, it is believed to have evolved from an australopithecine ancestor though which is disputed. Possibilities include the South African Australopithecus africanus and Australopithecus afarensis from East Africa (or its probable descendant species Australopithecus garhi). The famous ‘Lucy’ belongs to Australopithecus afarensis. In comparison to a modern human, Homo habilis was small brained and its limb proportions (short legs, long arms) were still very apelike. However, the skull was less massively-built than an australopithecine; the upper and lower jawbones were within the human size range; and the feet and thumb joints were humanlike (Conroy, 1997). Homo habilis is known in the fossil record from 2.33 to 1.44 million years ago (Kimbel, et al., 1997; Spoor, et al., 2007). It is then presumed to have given rise to Homo erectus. Although still small-brained in comparison to a modern human, the limb proportions of Homo erectus are similar to those of later humans. Homo erectus first appears in the fossil record 1.8 to 1.9 million years ago (Wood, 2011).

This conventional view has a number of problems. Firstly, a second species, Homo rudolfensis is now known to have been contemporary with Homo habilis. First proposed in 1972, it was confirmed as a separate species in 2012 (Leakey, et al., 2012). How Homo rudolfensis fits into the bigger picture is far from clear: some have noted similarities to an earlier hominin, Kenyanthropus platyops (‘Flat-faced man of Kenya’) and it is possible that Homo rudolfensis belongs in Kenyanthropus rather than Homo.

Another problem is that the earliest example of Homo habilis, a 2.33 million year old upper jawbone known as AL 666-1 from Hadar, Ethiopia might in fact be something other than Homo habilis. The oldest uncontested example of Homo habilis is only 1.9 million years old (Lieberman, 2007) and given that the species also persisted well after the appearance of Homo erectus an ancestor/descendant relationship seems unlikely. Instead, it has been suggested that the two species shared a common ancestor (Spoor, et al., 2007).

Finally, it has been suggested that the late australopithecine species Australopithecus sediba from South Africa, which dates to around 2 million years old (Pickering, et al., 2011) is a more plausible ancestor for Homo erectus than is Homo habilis (Berger, et al., 2010).

Could LD 530-1 be an australopithecine?

The date of 2.8 million years ago puts it just after the time of Australopithecus afarensis (3.9 to 3.0 million years ago) and before the late australopithecine species Australopithecus garhi (2.5 million years ago).Given that the Australopithecus garhi is thought to descendant of Australopithecus afarensis, LD 350-1 is in the right place at the right time to be a part of that lineage. In terms of size, both the jawbone and the teeth are within the Australopithecus afarensis range, albeit towards the lower end. However, most other respects, the mandibular and dental characteristics of LD 350-1 fall outside the range for Australopithecus afarensis. The dentition is also reduced (and therefore more humanlike) in comparison to Australopithecus garhi, which would appear to bump the latter from the lineage leading to Homo. Overall, LD 350-1 appears to be transitional between Australopithecus and Homo and is likely to represent the earliest-known example of the latter.

What are the implications if LD 350-1 is indeed Homo?

Models that posit an australopithecine ancestor for Homo from the period 2.5 to 2.0 million years ago (e.g. Australopithecus garhi or Australopithecus sediba) would be ruled out. Instead, Homo diverged from Australopithecus much earlier than hitherto believed. Notably, 2.8 million years ago coincides with a shift to a more arid climate in Africa, suggesting a link between climate change and the emergence of Homo. The fossil record of Ledi-Geraru records a shift to a more open habitat of grasses or low shrubs at around this time.

Reboot for Homo habilis

In a separate study, published in the journal Nature, Fred Spoor and colleagues (Spoor, et al., 2015) carried out a reconstruction of the 1.8 million year old Homo habilis holotype specimen OH 7. The results suggest that the species was larger-brained than previously believed, within the range of Homo erectus. It was also found that the dentition of OH 7 is more primitive than the 2.33 million year old AL 666-1, suggesting that the latter cannot be Homo habilis – but implying that the origins of Homo habilis go back even further. The study did not consider the affinities of AL 666-1 any further but speculated that it could be early Homo erectus. By 2.33 million years ago, the Homo lineage was already apparently diverse, with early human species distinguished from one another more by gnathic morphology than by brain size. The reporting of the early Homo jawbone LD 350-1 dovetails neatly with this study.

What species is LD 350-1?

It is more primitive than Homo habilis but nevertheless lies within Homo. Its describers did not assign a species to it, but it is likely that it will be eventually recognised as a new species within Homo; the earliest human species yet. 

References:

1.      Berger, L. et al., 2010. Australopithecus sediba: A New Species of Homo-Like Australopith from South Africa. Science, 9 April, Volume 328, pp. 195-204.

2.       Conroy, G., 1997. Reconstructing Human Origins: A Modern Synthesis. New York, NY: W. W. Norton & Company, Inc..

3.       DiMaggio, E. et al., 2015. Late Pliocene fossiliferous sedimentary record and the environmental context of early Homo from Afar, Ethiopia. Science, 5 March.

4.       Kimbel, W., Johanson, D. & Rak, Y., 1997. Systematic Assessment of a Maxilla of Homo From Hadar, Ethiopia. American Journal of Physical Anthropology, Volume 103, pp. 235-262.

5.       Leakey, M. et al., 2012. New fossils from Koobi Fora in northern Kenya confirm taxonomic diversity in early Homo. Nature, 9 August, Volume 488, pp. 201-204.

6.       Lieberman, D., 2007. Homing in on early Homo. Nature, 20 September, Volume 449, pp. 291-292.

7.       Pickering, R. et al., 2011. Australopithecus sediba at 1.977 Ma and Implications for the Origins of the Genus Homo. Science, 9 September, Volume 333, pp. 1421-1423.

8.       Spoor, F. et al., 2015. Reconstructed Homo habilis type OH 7 suggests deep-rooted species diversity in early Homo. Nature, 5 March, 7541(519), pp. 83-86.

9.       Spoor, F. et al., 2007. Implications of new early Homo fossils from Ileret, east of Lake Turkana, Kenya. Nature, 9 August, Volume 448, pp. 688-691.

10.    Villmoare, B. et al., 2015. Early Homo at 2.8 Ma from Ledi-Geraru, Afar, Ethiopia. Science, 5 March.

11.    Wood, B., 2011. Did early Homo migrate “out of ” or “in to” Africa?. PNAS, 28 June, 108(26), p. 10375–10376.

Archaic human recovered from seabed off western coast of Taiwan

Could partial lower jawbone be from a Denisovan – or an entirely new species?

A partial fossil human jawbone from Taiwan is reportedly the first archaic hominin to be found there. The jawbone was dredged by a fishing net from the 60 to 120 m (200 to 400 ft.) deep Penghu Channel, 25 km (15.5 miles) of the island’s western coast. Also recovered were vertebrate fossils known as the terminal Middle/Late Pleistocene ‘Penghu fauna’. Both Taiwan and the Penghu Channel were part of the Asian mainland during Pleistocene episodes of lowered sea levels. The jawbone found its way to an antique shop in Tainan City, where it was purchased by a local man who in turn donated it to the National Museum of Natural Science of Taiwan.

The nature of its recovery means that there is no stratigraphic data by which the Penghu 1 jawbone can be dated. Accordingly, researchers measured its fluorine and sodium content in relation to that of other Penghu fossils. Fluorine, deriving from the surroundings, tends to accumulate slowly over time in buried bones; sodium on the other hand exists at about one percent in the bones of living vertebrates, but decreases when they are fossilised. By this means, the researchers matched Penghu 1 with fossil remains of Crocuta crocuta ultima, an extinct Eurasian subspecies of the spotted hyena that reached northern China between 500,000 and 250,000 years ago, but did not reach southern China until 240,000 years ago. There were episodes of lowered sea levels between 190,000 to 130,000 years ago and from 70,000 to 10,000 years ago; Penghu 1 probably dates to one of these two intervals.

Penghu 1 is identified as archaic by its relatively large molars and premolars, and by its lack of a chin. The short and relatively wide shape of its dental arcade is derived in comparison to the earliest humans (Homo habilis and the Dmanisi hominins), but other than that it cannot readily be assigned to any particular archaic human species. The second molar is larger than those of other archaic Asian hominins, and the low, thick body is closer to some examples African and European Homo from 400,000 years ago than to Early/Middle Pleistocene Asian Homo, with the exception of the 400,000-year-old Chinese Hexian Homo erectus remains.

The large second molar suggests Denisovan affinities in M2 crown size, but unfortunately no Denisovan lower jawbones or lower M2 teeth have yet been found for comparison. Not until we have a Denisovan lower jawbone that can be identified as such by genetic means will we have a better idea if Penghu 1 belonged to a Denisovan.  Nor can we rule out the possibility that Penghu 1 represents a completely new archaic human species.

Reference:

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Chang, C. et al., The first archaic Homo from Taiwan. Nature Communications 6, 6037 (2015).

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