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Homo naledi

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Homo naledi
Temporal range: not dated
Holotype specimen of Homo naledi, Dinaledi Hominin 1 (DH1)
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Mammalia
Order:
Primates
Family:
Hominidae
Genus:
Homo
Species:
†H. naledi
Binomial name
Homo naledi
Berger et al., 2015[1]

Homo naledi is an extinct species of hominin assigned to the genus Homo, discovered within the Dinaledi Chamber of the Rising Star Cave system, which is located in the Cradle of Humankind, South Africa. The cave system is approximately 800 m (0.50 mi) southwest of Swartkrans (Afrikaans for “black cliff”), and within the same region as the well-known hominin-bearing sites of Sterkfontein (Afrikaans for “strong spring”) and Kromdraai (Afrikaans for “crooked turn”).[1]

The species is characterized by a body mass and stature similar to small-bodied human populations, a smaller endocranial volume similar to Australopithecus, and a cranial morphology (skull shape) similar to early Homo species. The skeletal anatomy combines primitive features known from australopithecines with features known from early hominins. The fossil bones in the cave include elements from at least 15 different individuals. The individuals show signs of having been deliberately disposed of within the cave near the time of death. The fossils themselves are not yet dated, but the lineage they belong to is estimated at 2.5 million years old.[1] The discoverers propose the bones represent a new species in the genus Homo, while other experts contend further analysis is needed to support or falsify this hypothesis.[2][3]

Etymology

The word naledi means "star" in the Sesotho and Setswana languages, two of the eleven national languages of South Africa, and refers to the fossils’ origin in the Dinaledi Chamber of the Rising Star cave system.[1]

Discovery

Illustration of the Dinaledi Chamber within Rising Star Cave, where H. naledi was recovered

In 2013, two Speleological Exploration Club of South Africa (SEC) members, Rick Hunter and Steven Tucker, who were working with scientists from the University of the Witwatersrand, including Pedro Boshoff, discovered the Dinaledi Chamber and the first specimens of H. naledi. While searching for an extension of the well-known Rising Star portion of the Westminster cave system, Hunter and Tucker found a narrow, vertically oriented "chimney" or "chute" measuring 12 m (39 ft) long with an average width of 20 cm (7.9 in).[4][5][6] Rather than a cave extension, Tucker and Hunter discovered a room 30 m (98 ft) underground (Site U.W. 101, the Dinaledi Chamber), the surface of which was littered with fossil bones.[6]

Fossil excavation

In November 2013, following an initial three-week-long excavation led by American and South African paleoanthropologist Lee R. Berger (National Geographic/University of the Witwatersrand Rising Star Expedition), 1,550 bone and teeth specimens belonging to H. naledi were uncovered.[7] Further excavations during March of 2014 recovered additional specimens. The finds were announced to the public two years later almost to the date on 10 September 2015.[1][4][8]

The remains of fifteen individuals, comprising 1,550 specimens—the largest set of human fossils ever found in Africa[9]—were found within clay-rich sediments during the initial investigation, and the layered distribution of the bones suggests that they had been deposited over a long time, perhaps centuries.[4] Scientists believe that there are many more remains to be found at the site.[10] The finds are considered the property of the South African people, and will probably remain in the country.[11]

The fossils include skulls, jaws, ribs, teeth, bones of an almost complete foot, of a hand, and of an inner ear. The bones of old, young and infants were found. Infants were identified by the small vertebrae.[4] Some of the bones resemble modern human bones, and other bones are more primitive than the australopithecine, an early ancestor of humans. The thumb, wrist and palm bones are modern-like while the fingers are curved, more australopithecine, and useful for climbing.[4] With the number of individuals, and the sexes and age groups represented, scientists consider the find to be "the richest assemblage of associated fossil hominins ever discovered in Africa, and aside from the Sima de los Huesos collection and later Neanderthal and modern human samples, it has the most comprehensive representation of skeletal elements across the lifespan, and from multiple individuals, in the hominin fossil record".[1]

Field work

On 6 October 2013, Lee Berger distributed a call over social media platforms Facebook, Twitter, and LinkedIn[12] for experienced paleoanthropologists with a unique skill set that involved cave and climbing experience. Candidates also were required to be "skinny and preferably small".[6][13] Of almost 60 scientists worldwide that responded, six female researchers were chosen that fitted these criteria. Dubbed "the Underground Astronauts", these early-career scientists included K. Lindsay Eaves (now Hunter), Marina Elliott, Elen Feuerriegel, Alia Gurtov, Hannah Morris, and Becca Peixotto.[14][15]

Morphology and interpretations

Two views of a hand
Foot in dorsal (A) and side (B) views. Scale bar = 10 cm

The physical characteristics of H. naledi present traits similar to the genus Australopithecus, mixed with traits more characteristic of the genus Homo, as well as traits not known in other hominin species.[1]

H. naledi stood approximately 150 centimetres (4 ft 11 in) tall, its stature falling within the range of small-bodied modern humans. Adult males stood around 150 cm (5 ft) tall and weighed around 45 kg (100 lb), while females were a little shorter and weighed a little less. An analysis of H. naledi's skeleton suggests it stood upright and was fully bipedal. Its hip mechanics are similar to australopithecines, but its feet and ankles are more similar to the genus Homo.[1]

However, the species' brains were markedly smaller than modern Homo sapiens, measuring between 450 and 550 cm3 (27–34 cu in). Four skulls were discovered, thought to be two females and two males, with a cranial volume of 560 cm3 (34 cu in) for the males and Template:Covert for females, approximately half the volume of modern human skulls; average Homo erectus skulls are 900 cm3 (55 cu in). The H. naledi skulls are closer in cranial volume to australopithecine skulls.[4] Nonetheless, the cranial structure is described as more similar to those found in the genus Homo than to australopithecines, particularly in its slender features, and the presence of temporal and occipital bossing, and the fact that the skulls do not narrow in behind the eye-sockets.[1] The teeth and mandible musculature are much smaller than those of most australopithecines, which suggests a diet that did not require heavy mastication.[1]

The hands of H. naledi appear to have been better for object manipulation than those of australopithecines.[1] However, the structure of the upper body seems to have been more primitive than that of other members of the genus Homo, even apelike.[4]

It is thought the bones are of members of one taxonomic family, as their features are strikingly similar.[10] The overall anatomical structure of the species has prompted scientists to classify the species within the genus Homo, rather than within the genus Australopithecus. Nonetheless, the proposal of assigning H. naledi a status as a separate species within Homo is not yet fully accepted. For example, paleoanthropologist Tim D. White commented that, based on the published descriptions, the fossils could well be considered to fall within the variation of the species Homo erectus, and his concern was echoed by paleoanthropologist Eric Delson. Berger rejected the possibility of the fossils representing the species H. erectus.[16]

The H. naledi skeletons indicate that the origins of the genus Homo were complex and may be polyphyletic, and that the species may have evolved separately in different parts of Africa.[17]

Age estimates

The Rising Star fossil assemblage itself is as yet undated. More primitive aspects of Homo naledi's anatomy, such as the smaller brain volume, suggest the species evolved near or at the beginning of the genus Homo 2.5 million to 2.8 million years ago. Geologists think the cave in which the fossils were discovered is no older than three million years.[18] The exact significance of the find for the scientific understanding of human evolution may depend on whether the fossils turn out to be significantly older or younger than the period in which Homo habilis, until now the earliest member of the genus Homo, emerged.[16]

Possible behavior

Experts speculate that, because the bones were discovered together, the species members were disposing of dead bodies in the cave as a ritualistic behaviour, a sign of symbolic thought.[19] If correct, this would be remarkable since this type of behavior has been generally considered to have emerged much later, among Homo sapiens and Homo neanderthalensis.[4] "Ritual" here means an intentional and repeated practice, disposing of dead bodies in the cave, and not meaning any type of religious ritual.[18]

Berger thinks that deliberate disposal of bodies within the intricate cave system would have required the hominins to find their way through total darkness and back again, and he speculates that this would have required light in the form of torches or fires lit at intervals.[4]

Documentary

A PBS NOVA National Geographic documentary Dawn of Humanity, describing the discovery of H. naledi, was put online on 10 September 2015, and will be broadcast on 16 September 2015.[20]

See also

References

  1. ^ a b c d e f g h i j k Berger, Lee R.; et al. (10 September 2015). "Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa". eLife. 4. doi:10.7554/eLife.09560. Retrieved 10 September 2015. {{cite journal}}: Unknown parameter |laysummary= ignored (help)CS1 maint: unflagged free DOI (link)
    Full list of authors
    • Lee R Berger
    • John Hawks
    • Darryl J de Ruiter
    • Steven E Churchill
    • Peter Schmid
    • Lucas K Delezene
    • Tracy L Kivell
    • Heather M Garvin
    • Scott A Williams
    • Jeremy M DeSilva
    • Matthew M Skinner
    • Charles M Musiba
    • Noel Cameron
    • Trenton W Holliday
    • William Harcourt-Smith
    • Rebecca R Ackermann
    • Markus Bastir
    • Barry Bogin
    • Debra Bolter
    • Juliet Brophy
    • Zachary D Cofran
    • Kimberly A Congdon
    • Andrew S Deane
    • Mana Dembo
    • Michelle Drapeau
    • Marina C Elliott
    • Elen M Feuerriegel
    • Daniel Garcia-Martinez
    • David J Green
    • Alia Gurtov
    • Joel D Irish
    • Ashley Kruger
    • Myra F Laird
    • Damiano Marchi
    • Marc R Meyer
    • Shahed Nalla
    • Enquye W Negash
    • Caley M Orr
    • Davorka Radovcic
    • Lauren Schroeder
    • Jill E Scott
    • Zachary Throckmorton
    • Matthew W Tocheri
    • Caroline VanSickle
    • Christopher S Walker
    • Pianpian Wei
    • Bernhard Zipfel
  2. ^ Sample, Ian (10 September 2015). "Homo naledi: New species of ancient human discovered, claim scientists". The Guardian. Retrieved 10 September 2015.
  3. ^ Greenfieldboyce, Nell (10 September 2015). "South African Cave Yields Strange Bones Of Early Human-Like Species". NPR. Retrieved 10 September 2015.
  4. ^ a b c d e f g h i Shreeve, Jamie (10 September 2015). "This Face Changes the Human Story. But How?". National Geographic News. Retrieved 10 September 2015.
  5. ^ Dirks, P.H. G. M.; Berger, L. R.; Roberts, E. M.; Kramers, J. D.; Hawks, J.; Randolph-Quinney, P. S.; Elliott, M.; Musiba, C. M.; Churchill, S. E.; de Ruiter, D. J.; Schmid, P.; Backwell, L. R.; Belyanin, G. A.; Boshoff, P.; Hunter, K. L.; Feuerriegel, E. M.; Gurtov, A.; du G. Harrison, J.; Hunter, R.; Kruger, A.; Morris, H.; Makhubela, T. V.; Peixotto, B.; Tucker, S. (10 September 2015). "Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa". eLife. 4: e09561. doi:10.7554/eLife.09561. ISSN 2050-084X. PMC 4559842.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  6. ^ a b c Tucker, Steven (13 November 2013). "Rising Star Expedition". Speleological Exploration Club. Retrieved 8 September 2015.
  7. ^ Howley, Andrew (6 November 2013). "Rising Star Expedition: Prehistory in the Making". National Geographic Society. Retrieved 8 September 2015.
  8. ^ Feltman, Rachel (10 September 2015). "Meet the six female 'underground astronauts' who recovered our newest relative". Washington Post. Retrieved 10 September 2015.
  9. ^ Wong, Kate (10 September 2015). "Mysterious New Human Species Emerges from Heap of Fossils". Scientific American. Retrieved 10 September 2015.
  10. ^ a b Alford, Justine (10 September 2015). "New Species Of Human Discovered In South Africa". IFL Science. {{cite web}}: External link in |website= (help)
  11. ^ Nutt, Amy Ellis (10 September 2015). "Scientists shocked the world with a brand new species of man — but who owns the bones?". Washington Post. Retrieved 10 September 2015.
  12. ^ Gibbons, Ann (10 September 2015). "New human species discovered". Science (journal). Retrieved 11 September 2015.
  13. ^ Dave Ingold (6 December 2013). "Rising Star Expedition Finds Over 1,000 Hominid Fossils". Speleological Exploration Club. Retrieved 8 September 2015.
  14. ^ Staff (6 November 2013). "Rising Star Expedition Launched". University of the Witwatersrand. Retrieved 8 September 2015.
  15. ^ Brahic, Catherine (26 November 2014). "Bone Bonanza: Chamber of Secrets Yields Human Remains". New Scientist. Retrieved 8 September 2015.
  16. ^ a b Staff (10 September 2015). "Bones of Homo naledi, new human relative, found in South African cave". AP News. Retrieved 10 September 2015.
  17. ^ Stringer, Chris (10 September 2015). "The many mysteries of Homo naledi". eLife. 4: e10627. doi:10.7554/eLife.10627. ISSN 2050-084X. PMC 4559885.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  18. ^ a b Wilford, John Noble (10 September 2015). "New Species in Human Lineage Is Found in a South African Cave". New York Times. ISSN 0362-4331. Retrieved 10 September 2015.
  19. ^ Ghosh, Pallab (10 September 2015). "New human-like species discovered in S Africa". BBC News. Retrieved 10 September 2015.
  20. ^ Staff. "Dawn of Humanity". PBS. Retrieved 10 September 2015.
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