Homo Naledi

'' Homo naledi'' is an extinct species of archaic human discovered in 2013 in the Rising Star Cave, Cradle of Humankind, South Africa dating to the Middle Pleistocene 335,000–236,000 years ago. The initial discovery comprises 1,550 specimens, representing 737 different elements, and at least 15 different individuals. Despite this exceptionally high number of specimens, their classification with other ''Homo'' remains unclear.

Along with similarities to contemporary ''Homo'', they share several characteristics with the ancestral ''Australopithecus'' and early ''Homo'' as well (mosaic evolution), most notably a small cranial capacity of 465–610 cm³ (28.4–37.2 cu in), compared to 1,270–1,330 cm³ (78–81 cu in) in modern humans. They are estimated to have averaged in height and in weight, yielding a small encephalization quotient of 4.5. Nonetheless, ''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 arboreal than other ''Homo'', better adapted to climbing and suspensory behaviour in trees than endurance running. Tooth anatomy suggests consumption of gritty foods covered in particulates such as dust or dirt. Though they have not been associated with stone tools or any indication of material culture, they appear to have been dextrous enough to produce and handle tools, and likely manufactured Early or Middle Stone Age industries. It has also been controversially postulated that these individuals were given funerary rites, and were carried into and placed in the chamber. In December 2022, suggestions that ''H. naledi'' used fire for light and cooking were reported.

Discovery

On 13 September 2013 while exploring the Rising Star Cave system in the Cradle of Humankind, South Africa, cavers Rick Hunter and Steven Tucker found hominin fossils at the bottom of the Dinaledi Chamber. On the 24th, they returned to the chamber and took photos, which they showed to South African palaeoanthropologists Pedro Boshoff and Lee Rogers Berger on October 1. Berger subsequently assembled an excavation team which included Hunter and Tucker, the so-called "Underground Astronauts".

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. It lies about from the main entrance, at the bottom of a vertical drop, and the long main passage is only at its narrowest. In total, more than 1,550 pieces of bone belonging to at least fifteen individuals (9 immature and 6 adults) have been recovered from the clay-rich sediments. Berger and colleagues published the findings in 2015.

The fossils represent 737 anatomical elements – including the parts of the skull, jaw, ribs, teeth, limbs, and inner ear bones – from old, adult, young, and infantile individuals. There are also some articulated or near-articulated elements, including the skull with the jaw bone, and nearly complete hands and feet. With the number of individuals of both sexes across several age demographics, it is the richest assemblage of associated fossil hominins discovered in Africa. Aside from the 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.

The holotype specimen, DH1, comprises a male partial calvaria (top of the skull), partial maxilla, and nearly complete jawbone. The paratypes, DH2 through DH5, all comprise partial calvaria. Berger and colleagues named the species ''Homo naledi'', the species name meaning "star" in the Sotho language, because the remains came from Rising Star Cave.

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.

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. The fossils were previously thought to have dated to 1~2 million years ago because no similarly small-brained hominins had previously been known from such a recent date in Africa (the smaller-brained ''Homo floresiensis'' of Indonesia lived on an isolated island, and apparently went extinct shortly after the arrival of modern humans.) 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. Their mosaic anatomy also greatly expands the range of variation for the genus.

''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 '' H. habilis'', ''H. rudolfensis'', and ''A. sediba''; are a 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

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