Homo naledi

This is a good article. Click here for more information.
Source: Wikipedia, the free encyclopedia.

Homo naledi
Temporal range:
Ma[1]
↓
The 737 known elements of H. naledi
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Suborder: Haplorhini
Infraorder: Simiiformes
Family: Hominidae
Subfamily: Homininae
Tribe: Hominini
Genus: Homo
Species:
†H. naledi
Binomial name
†Homo naledi
Berger
et al., 2015
Location of Rising Star Cave in the Cradle of Humankind, South Africa

Homo naledi is an

Middle Pleistocene 335,000–236,000 years ago. The initial discovery comprises 1,550 specimens of bone, representing 737 different skeletal elements, and at least 15 different individuals. Despite this exceptionally high number of specimens, their classification with other Homo
species remains unclear.

Along with similarities to contemporary Homo, they share several characteristics with the ancestral Australopithecus as well as early Homo (mosaic evolution), most notably a small cranial capacity of 465–610 cm3 (28.4–37.2 cu in), compared with 1,270–1,330 cm3 (78–81 cu in) in modern humans. They are estimated to have averaged 143.6 cm (4 ft 9 in) in height and 39.7 kg (88 lb) in weight, yielding a small encephalization quotient of 4.5. H. naledi brain anatomy seems to have been similar to contemporary Homo, which could indicate comparable cognitive complexity. The persistence of small-brained humans for so long in the midst of bigger-brained contemporaries revises the previous conception that a larger brain would necessarily lead to an evolutionary advantage, and their mosaic anatomy greatly expands the known range of variation for the genus.

H. naledi anatomy indicates that, though they were capable of long-distance travel with a humanlike stride and gait, they were more

Early or Middle Stone Age industries
since no other human species in the vicinity at that time has been discovered. It has also been controversially postulated that these individuals were given funerary rites, and were carried into and placed in the chamber.

Discovery

Dinaledi Chamber
in yellow and the Lesedi Chamber in red

On 13 September 2013 while exploring the

Lee Rogers Berger on October 1.[2] Berger assembled an excavation team which included Hunter and Tucker, the so-called "Underground Astronauts".[3]

The chamber had been entered at least once before, by cavers in the early 1990s. They rearranged some bones and may have caused further damage, although much of the floor in the chamber had not been walked on prior to 2013.[4] It lies about 80 m (260 ft) from the main entrance, at the bottom of a 12 m (39 ft) vertical drop, and the 10 m (33 ft) long main passage is only 25–50 cm (10 in – 1 ft 8 in) at its narrowest.[4] In total, more than 1,550 pieces of bone belonging to at least fifteen individuals (9 immature and 6 adults)[5] have been recovered from the clay-rich sediments. Berger and colleagues published the findings in 2015.[6]

The fossils represent 737 anatomical elements – including portions of the skull, jaw, ribs, teeth, limbs, and inner ear bones – from old, adult, young, and infantile individuals. There are also some

Sima de los Huesos collection and later Neanderthal and modern human samples, the excavation site has the most comprehensive representation of skeletal elements across the lifespan, and from multiple individuals, in the hominin fossil record.[6]

The

jawbone. The paratypes, DH2 through DH5, all comprise partial calvaria. Berger and colleagues named the species Homo naledi in 2015, the specific name meaning "star" in the Sotho language, because the remains came from Rising Star Cave.[6]

The remains of at least three additional individuals (two adults and a child) were reported in the Lesedi Chamber of the cave by John Hawks and colleagues in 2017.[7]

Classification

In 2017, the Dinaledi remains were dated to 335,000–236,000 years ago in the

Middle Pleistocene, using electron spin resonance (ESR) and uranium–thorium (U-Th) dating on three teeth, and U-Th and paleomagnetic dating of the sediments they were deposited in.[1] The fossils were previously thought to have dated to 1–2 million years ago[6][8][9][3] because no similarly small-brained hominins had previously been known from such a recent date in Africa.[10] The smaller-brained Homo floresiensis of Indonesia lived on an isolated island, and apparently became extinct shortly after the arrival of modern humans.[11]

The ability of such a small-brained hominin to have survived for so long in the midst of bigger-brained Homo greatly revises previous conceptions of human evolution and the notion that a larger brain would necessarily lead to an evolutionary advantage.[10] Their mosaic anatomy also greatly expands the range of variation for the genus.[12]

H. naledi is hypothesised to have branched off very early from contemporaneous Homo. It is unclear whether they branched off at around the time of

sister taxon to H. erectus and the contemporaneous large-brained Homo, or are a sister taxon to the descendants of H. heidelbergensis (modern humans and Neanderthals). This would mean that they branched off from contemporary Homo at latest before 900,000 years ago, and possibly as early as the Pliocene. It is also possible their ancestors speciated after an interbreeding event between Homo and late australopithecines.[10] Looking at the skull, H. naledi has the closest affinities to H. erectus.[12]

H. erectus georgicus, and H. floresiensis
.

It is unclear if these H. naledi were an isolated population in the Cradle of Humankind, or if they ranged across Africa. If the latter, then several gracile hominin fossils across Africa which have traditionally been classified as late H. erectus could potentially represent H. naledi specimens.[13]

Anatomy

Skull

Different views of LES1

Two male H. naledi skulls from the Dinaledi chamber had cranial volumes of about 560 cm3 (34 cu in), and two female skulls 465 cm3 (28.4 cu in). A male H. naledi skull from the Lesedi chamber had a cranial volume of 610 cm3 (37 cu in). The Dinaledi specimens are more similar to the cranial capacity of australopithecines. For comparison, H. erectus averaged about 900 cm3 (55 cu in),

H. e. georgicus. The encephalization quotient of H. naledi was estimated at 3.75, which is the same as the pygmy H. floresiensis, but notably smaller than all other Homo. Contemporary Homo were all above 6, H. e. georgicus at 3.55, and A. africanus at 3.81.[15] It is unclear if H. naledi inherited small brain size from the last common Homo ancestor, or if it was evolved secondarily more recently.[16]

The skull shape is more similar to Homo, with a slenderer shape, the presence of temporal and occipital lobes of the brain, and reduced post-orbital constriction, with the skull not becoming narrower behind the eye-sockets.[6][16] The frontal lobe morphology is more or less the same in all Homo brains despite size, and differs from Australopithecus, which has been implicated in the production of tools, the development of language, and sociality.[16]

Like modern humans, but unlike fossil hominins, including South African australopithecines, H. erectus, and Neanderthals, the permanent 2nd molar erupted comparatively late in life, emerging alongside the premolars instead of before, which indicates a slower maturation unusually comparable to modern humans.[17] The tooth formation rate of the front teeth is also most similar to modern humans.[18] The overall size and shape of the molars most closely resemble those of three unidentified Homo specimens from the local Swartkrans and East African Koobi Fora Caves, and are similar in size (but not shape) to Pleistocene H. sapiens. The necks of the molars are proportionally similar to those of A. afarensis and Paranthropus.[19]

Unlike modern humans and contemporary Homo, H. naledi lacks several accessory dental features, and has a high frequency of individuals who present main

hypocone (to the right on the lip-side) on the 2nd and 3rd molars, and a Y-shaped hypoconulid (a ridge on the lip-side towards the cheek) on all three molars. Nonetheless, H. naledi also has many dental similarities with contemporary Homo.[20]

The anvil (a middle ear bone) more resembles those of chimps, gorillas, and Paranthropus than Homo.[21] Like H. habilis and H. erectus, H. naledi has a well-developed brow-ridge with a fissure stretching across just above the ridge, and like H. erectus a pronounced occipital bun. H. naledi has some facial similarities with H. rudolfensis.[20]

Build

A skeletal reconstruction of the juvenile DH7 – Scale 10 cm (4 in)

The H. naledi specimens are estimated to have, on average, stood around 143.6 cm (4 ft 9 in) and weighed 39.7 kg (88 lb). This body mass is intermediate between what is typically seen in Australopithecus and Homo species. Like other Homo, male and female H. naledi were likely about the same size, males on average about 20% larger than females.

Turkana boy (H. ergaster). Because dental development is so similar to that of modern humans, a slower maturation rate is not completely out of the question. Using the faster growth rate, DH7 would have died at 8–11 years old, but using the slower growth, DH7 would have died at 11–15 years old.[22]

Concerning the

intercostal muscles above, and a strong quadratus lumborum muscle below. Unlike Neanderthals, there was weak attachment to the diaphragm. Overall, this H. naledi specimen appears to have been small-bodied compared with other Homo species, though it is unclear if this single specimen is representative of the species.[23]

The shoulders are more similar to those of australopithecines, with the

arboreal.[23]

Limbs

Fossil right hand of H. naledi (bottom view left, top view right) – Scale 5 cm (2 in)
Fossil right foot of H. naledi, A) top view, B) left-side view, C) arch – Scale 10 cm (3.9 in)

The

phalangeal joint is flattened. The distal thumb phalanx bone is robust, and proportionally more similar to those of H. habilis and P. robustus.[26]

The metacarpals of the other fingers share adaptations with modern humans and Neanderthals to be able to cup and manipulate objects, and the

Qafzeh cave, Israel, which is consistent with climbing behaviour.[26]

H. naledi was a

ankle bone has a low declination, which possibly indicate the foot would have been subtly stiffer during the stance phase of walking before the foot pushed off the ground.[27]

Pathology

The adult right

benign tumour. The individual would have experienced some swelling and localised discomfort, but the tumour's position near the medial pterygoid muscle (likely causing discomfort on the jaw hinge) may have impeded function of the muscle, and changed elevation of the right side of the jaw.[28]

Dental defects in H. naledi specimens during 1.6–2.8 and 4.3–7.6 months of development were most likely caused by seasonal stressors. This may have been due to extreme summer and winter temperatures causing food scarcity. Minimum winter temperatures of the area average about 3 °C (37 °F), and can drop below freezing. Staying warm for an infant of the small-bodied H. naledi would have been difficult, and winters likely increased susceptibility to respiratory diseases. Environmental stressors are consistent with present-day

diarrhoea hospitalisation being most frequent at the height of the rainy season in summer.[29]

Local hominins were likely preyed upon by large carnivores, such as lions, leopards, and hyaenas. There seems to be a distinct paucity of large carnivore remains from the northern end of the Cradle of Humankind, where Rising Star Cave is located, possibly because carnivores preferred the Blaaubank River to the south which may have offered better hunting grounds with a greater abundance of large prey items. Alternatively, because many more sites are known in the south than the north, carnivore spatial patterns may not be well-represented by the fossil record (

preservation bias).[30]

Culture

A facial reconstruction of Homo naledi

Food

Dental chipping and wearing indicates the habitual consumption of small hard objects, such as dirt and dust, and cup-shaped wearing on the back teeth may have stemmed from gritty particles. These could have originated from unwashed roots and tubers. Alternatively, aridity could have stirred up particulates onto food items, coating food in dust. It is possible that they commonly ate larger hard items, such as seeds and nuts, but these were processed into smaller pieces before consumption.[31][32]

H. naledi occupied a seemingly unique niche from previous South African hominins, including Australopithecus and Paranthropus. The teeth of all three species indicate that they needed to exert high shearing force to chew through perhaps plant or muscle fibres. The teeth of other Homo cannot produce such high forces perhaps due to the use of some food processing techniques, such as cooking.[31]

Technology

H. naledi could have produced

Early Stone Age (Acheulean and possibly the earlier Oldowan) or Middle Stone Age industries because they have the same adaptations to the hand as other human species which are implicated in tool production.[10][15] H. naledi is the only identified human species to have existed during the early Middle Stone Age of the Highveld region, South Africa, possibly indicating that this species manufactured and maintained this tradition at least during this time period. In this scenario, such industries and stone cutting techniques would have evolved independently several times among different Homo species and populations, or were transported over long distances by the inventors or apprentices and taught.[10]

Funerals

Dinaledi Chamber, in the Rising Star Cave

In 2015, archaeologist Paul Dirks, Berger, and colleagues concluded that the bodies had to have been deliberately carried and placed into the chamber by people because they appear to have been intact when they were first deposited in the chamber. There is no evidence of trauma from being dropped into the chamber nor of predation, and there is exceptional preservation. The chamber is inaccessible to large predators, appears to be an isolated system, and has never been flooded. That is, natural forces were not at play.[4]

There is no hidden shaft through which people could have accidentally fallen in, and there is no evidence of some catastrophe which killed all the individuals inside the chamber. They said it is possible that the bodies were dropped down a chute and fell slowly due to irregularity and narrowness of the path down, or a soft mud cushion to land on. In whatever scenario, the morticians would have required artificial light to navigate the cave. The site was used repeatedly for burials as the bodies were not all deposited at the same time.[4]

In 2016, palaeoanthropologist Aurore Val countered that such preservation may have been due to

mummification rather than careful burial, and the absence of long bone heads is reminiscent of predation. She believes that discounting natural forces such as flooding for depositing the bodies is unjustified. She identified evidence of damage done by beetles, beetle larvae, and snails, which facilitate decomposition. The chamber does not present ideal conditions for snails, nor does it contain snail shells, which would indicate decomposition initiated before deposition in the chamber.[33]

In 2017, Dirks, Berger, and colleagues reaffirmed that there is no evidence of water flow into the cave, and that it is more likely that the bodies were deliberately deposited into the chamber. They said it is possible that they were deposited by contemporary Homo, such as the ancestors of modern humans, rather than other H. naledi, but that the cultural behaviour of funerary practises is not impossible for H. naledi. They proposed that placement in the chamber may have been done to remove decaying bodies from a settlement, prevent scavengers, or as a consequence of social bonding and grief.[10]

In 2018, anthropologist Charles Egeland and colleagues echoed Val's sentiments, and stated that there is insufficient evidence to conclude that a hominid species had developed a concept of the afterlife so early in time. They said that the preservation of the Dinaledi individuals is similar to those of baboon carcasses which accumulate in caves, either by natural death of cave-dwelling baboons, or by a leopard dragging in carcasses.[34]

In 2021, following the analysis of the bone fragments of an immature individual, Juliet Brophy and Berger again stated that the H. naledi remains were purposefully interred by some human species.[35] This would make Homo naledi the oldest evidence of burial by hominids.[36] The findings are disputed.[37]

Gallery

Skeletal elements
  • (A,B) Digitally reconstructed skull sides
    (A,B) Digitally reconstructed
    skull sides
  • Lower jaws of LES1 (left) and DH1 (right)
    Lower jaws of
    LES1 (left) and DH1 (right)
  • Upper jaws of LES1 (left) and DH1 (right)
    Upper jaws of
    LES1 (left) and DH1 (right)
  • (A,B,C,D) Views of one lower jaw
    (A,B,C,D) Views of one lower jaw
  • Views of one clavicle
    Views of one clavicle
  • Views of one humerus
    Views of one humerus
  • Views of one ulna
    Views of one ulna
  • Metacarpals from several individuals, each labeled
    Metacarpals
    from several individuals, each labeled
  • Views of a 10th thoracic vertebra
    Views of a 10th
    thoracic vertebra
  • Views of an 11th thoracic vertebra
    Views of an 11th
    thoracic vertebra
  • (A,B) ilium, (C,D) adolescent sacrum, (E,F) ischium
    (A,B) ilium, (C,D) adolescent sacrum, (E,F) ischium
  • Views of one femur
    Views of one femur
  • (A,B,C,D) Views of one tibia
    (A,B,C,D) Views of one tibia
  • Ankle bones from several individuals, each labeled
    Ankle bones
    from several individuals, each labeled
  • (1) adult right foot, (2) juvenile left, (3,4) adult left, (5) juvenile right
    (1) adult right foot, (2) juvenile left, (3,4) adult left, (5) juvenile right

See also

References

  1. ^
    PMID 28483040
    .
  2. ^ a b Tucker, Steven (13 November 2013). "Rising Star Expedition". Speleological Exploration Club. Retrieved 8 September 2015.
  3. ^
    doi:10.1511/2016.121.198. Archived from the original
    on 16 May 2017.
  4. ^
    PMID 26354289
    .
  5. doi:10.17159/sajs.2018/20170066
    .
  6. ^
    PMID 26354291
    .
  7. ^
    PMID 28483039
    .
  8. PMID 27457542
    .
  9. doi:10.17159/sajs.2015/a0124
    .
  10. ^
    PMID 28483041
    .
  11. S2CID 4469009
    .
  12. ^
    PMID 27836166
    .
  13. PMID 26354290
    .
  14. S2CID 21705705
    .
  15. ^
    PMID 28874266
    .
  16. ^
    PMID 29760068
    .
  17. PMID 26914367
    .
  18. S2CID 14006736
    .
  19. S2CID 109058795
    .
  20. ^
    PMID 29887210
    .
  21. S2CID 51618301
    .
  22. PMID 32236122
    .
  23. ^
    PMID 28094004
    .
  24. S2CID 2909448
    .
  25. ^
    PMID 27855981
    .
  26. ^
    PMID 26441219
    .
  27. PMID 26439101
    .
  28. S2CID 29150977
    .
  29. doi:10.17159/sajs.2019/5872
    .
  30. ^ Reynolds, S. C. (2010). "Where the Wild Things Were: Spatial and Temporal Distribution of Carnivores in the Cradle of Humankind (Gauteng, South Africa) in Relation to the Accumulation of Mammalian and Hominin Assemblages". Journal of Taphonomy. 8 (2–3): 233–257.[unreliable source?]
  31. ^
    PMID 29606200
    .
  32. S2CID 24296825
    .
  33. PMID 27039664
    .
  34. PMID 29610322
    .
  35. doi:10.48738/2021.iss1.64
    .
  36. ^ Davis, Josh (5 June 2023). "Claims that ancient hominins buried their dead could alter our understanding of human evolution".
  37. S2CID 260201327
    .

Further reading

External links

Wikimedia Commons has media related to Homo naledi.
Wikispecies has information related to Homo naledi.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Homo_naledi&oldid=1218642548"