Homo habilis

Credit: Julio Lacerda.

*Homo habilis* is an extinct species of hominin that lived in Eastern and Southern Africa during the Early Pleistocene.

## History

OH 7 is the first recognized *Homo habilis*. However OH 4 is the true first remains, but went unrecognized for some time. Oldman tools associated with it were originally assigned to *Zinjanthropus* in 1959 since it was the only hominin known from Olduvai. This was amended among the description of OH 7. Phillip V. Tobias and John R. Napier (1964) assigned the remains to *Homo* after recommendation. Raymond Dart then erected *H. habilis* (meaning "able/handy/mentally skillful/vigorous man"). The associated Oldowan industry was evidenced as great cognitive ability and as verification for *H. habilis* to belong to *Homo*. For a while after naming, it was debated whether this species should be classified as *Australopithecus* or even merged into *Australopithecus habilis*. This was partly due because *Homo* was thought to have evolved in Asia, so it was thought an ancestor with an age so old  from Africa was impossible. The brain was also smaller than Wilfred Le Gros Clark (1955) had considered when defining *Homo*. Nonetheless, the species gained recognition as more material was recovered. Tobias (1983) proposed *Australopithecus africanus* is the concestor of *Paranthropus* and *H. habilis*, and by effect, all descending *Homo* via cladogenesis. He also states a large leap between them since cranial capacity nearly doubles, hypothesizing a gradual evolution from then on. Some argued this new species was simply a male morph since all other specimens were females. Many other specimens have taxonomic questioning, sometimes bouncing between classification as *Homo erectus* and/or *Homo erectus*. Darren Curnoe (2010) suggested splitting many *H. habilis*, australopithecine and indeterminate specimens into *Homo guatengensis*. Many see little reason to consider this valid. OH 62 is the first postcrania, though fragmentary. Wood and Mark Collard (1999) suggested a recombination as *Australopithecus habilis*, subsequently. However, the conclusions drawn have been challenged by reanalysis. The discovery of Dmanisi has led to this species being lumped as *Homo erectus*. This conclusion is also often discredited.

## Classification

There is no common opinion if *H. habilis* is ancestral to *Homo erectus* or if it is an offshoot. Additionally, it is unknown if all specimens are assigned correctly. Still, it and *Homo rudolfensis* are commonly placed nearer to the bottom of the cladogram with no debate on the inclusion in the genus *Homo*. Many *Australopithecus* species have been proposed as an ancestor but it is unknown which truly is and when this happened. However, LD 350-1 suggests a split from *Australopithecus afarensis* at about the same time as its date. Some state this specimen is ancestor to *H. habilis*, but this is unclear. A.L. 666-1 is the oldest specimen but is more derived than the younger OH 7. This suggests derived and basal morphs coexisted. This suggests the lineage began before 2.3 million years ago. OH 13 is the youngest specimen, at 1.65 million years.

## Description

   Generally, it was thought brain size increased and rapidly between species transition. This would explain the theory that *H. habilis* evolved into *Homo erectus*. *H. habilis* has a cranial capacity of 500-900, as found by a 2015 study. This does indicate a jump from australopithecines. An expanded cerebrum is present. Striations in the teeth of OH 65 that slants right might have been self-inflicted while attempting to pull meat from its teeth while trying to cut it with a tool in its right hand. If this were true, this would indicate right handedness and handedness, which is associated with a reorganization of the brain and lateralization between both hemispheres of the brain. A similar scenario is proposed for some Neanderthal specimens. Lateralization is associated with tool usage and, weakly, language. The tooth rows are V-shaped, as opposed by later species. The face under the nose is prognathic, with everything above the nose flat.

   OH 62, a presumed female, and KNM-ER 3735, a presumed male, are fragmentary skeletons showing a morphology more similar to other hominids and even *A. afarensis*, consistent with an arboreal lifestyle. Due to this at least some arboreality is assumed. Based on OH 62 and australopiths, H. habilis is generally considered small-bodied. It is assumed pre-*Homo erectus* species have considerable sexual dimorphism. This species is thought to have thick body hair coverage since they appear to have lived in cooler environments and may have been less active than anything post *Homo erectus*, which are presumed hairless. Dental development rates assume an accelerated growth rate. This would be most similar to other hominids.

It's arms are considered to be proportionally longer and better for swinging and climbing. Martin Haeustler and Henry McHenry (2004) use the humerus-femur ratio of OH 62 to determine ape-like proportions are unfounded, with KNM-ER 3735 with near-apomorphic proportions. Still the humerus of OH 62 (258-270 millimeters long) and the ulnar (245-255 millimeters long) are closer to Pan. OH 7 displays precision gripping in the hand. The femur is traditionally compared with A.L. 288-1 in justification for giving it stouts. However,  Hassler and McHenry suggest OH 24, not of *H. habilis*, to be more apt for comparison. If it did have long, apomorphic-esque legs, it may have been effective for long-distance movement. However, the fossil is incomplete. OH 62 is close in thickness to Pan rather than *Homo erectus*, which may represent the differing load-bearing capabilities brought with arboreality in *H. habilis*. OH 35 has a strong fibula more like other hominids and consistent with arboreality and vertical climbing, though this specimen may be a *Paranthropus boisei*.

OH 8 is a foot better adapted for terrestriality more than *A. afarensis*, but is still rather ape-like with characters seen in climbing species. A projecting toe and compacted mid-foot joints indicate a restricted rotation in the foot and ankle. Stability enhances 5h3 force generated while running, which may indicate a degree of endurance running in *H. habilis*, contrary to hypotheses that state that evolved in *Homo erectus* or *Homo erectus*.

## Paleobiology

### Society

It is difficult to know how *H. habilis* lived with confidence. Additionally, many specimens with tentative gender are assumed from the size of robustness of the remains when the pelvis and other diagnostic bones are not preserved. Mating practices are perceivable from dental morphology, but this species presents a mosaic of morphology, making this method dubious. Tool and processed animal carcasses at Olduvai indicate these areas were a communal processing and consumption grounds rather than the nuclear family dynamic in apomorphic hunter gatherers. In most cases, the behaviour of *H. habilis* is inferred from savanna chimpanzees and baboons. These groups consist of several males that defend the group from threats, sometimes by throwing objects or engaging in group threat display. OH 7 appears to have been severed by a crocodile, maybe *Crocodylus anthropophagus*. OH 35 is either leg of *H. habilis* or *Paranthropus boisei* seems to bear signs of leopard predation. Olduvai hominids were likely preyed upon by hyenas and sabertooth cats. Leslie C. Airflow and Robin Dunbar (1993) estimated a group may have been of 70-85 individuals based on the neocortex and other hominids. *H. habilis* lived with *Homo rudolfensis* and *Paranthropus boisei*, but it is unknown how they interacted. The latter was associated with Oldowan tools, but it did not create them. To explain this, Leakey et al. suggested it was killed by *H. habilis* in a cannibalistic act. However, no evidence suggests this.

### Diet

*Homo habilis* likely scavenged rather than hunting, stealing prey from smaller predators. Fruit was probably also important in their diets based on dental erosion. They probably did not eat many tough items. They were likely generalistic omnivores with a greater proportion of meat, which led to brain growth. Two hypotheses exist: that meat allowed the brain to grow in order to more effectively steal carcasses, or that meat allowed the herbivores ape gut to decrease and for the saved energy towards brain growth. It is also suggested that, in a dry climate, they relied in underground foods like tubers and food sharing. This would have allowed members to have bonded. The gathering model explains brain growth but does not consider arboreality and other morphology . Large incisors compared to its ancestors suggest a reliance on them. The mandibular bodies are thicker, resisting more torsion. This suggests their jaws could withstand and produce great strength  the greater molar cusp relief suggests it used tools to fracture tough foods rather than wearing down teeth. Nonetheless, technological adaptation did not likely greatly effect the diet of *H. habilis*.

### Technology

Homo habilis is associated with the Oldowan culture that was mainly used to butcher and flay, but sometimes utilized for sawing or scraping wood and to cut soft plants. They appear to have selected lithic cores and had good knowledge of what rocks could break a certain way if struck with enough force in one spot. They created choppers, polyhedrons and discoids, although specific shapes were probably not curated before production (instead resulting from a lack of standardization and the use of certain raw materials). Spheroids are common in Olduvai, made from abundant large and soft quartz and quartzite; Koobi Fora lacks spheroids and mostly comprises of hard basalt lava rocks. Unlike the Acheulean of *Homo ergaster*, Oldowan does not require planning and foresight or high knapper cognition, but still requires much coordination and some mechanical data. These tools did not have retouching and were probably discarded after use in most cases. Oldowan was first detected in 1934, but not recognized as one of the earliest cultures until the 1960s, aging as far back as 2.6 million years ago with *Homo* sp.. However, australopithecines also made tools, as evidenced by the Lomekwian culture (the true earliest) associated with *Kenyanthropus*. Nonetheless, Oldowan is a major advancement in australopithecine culture in the use of sharp edges that could process a larger diet, which was advantageous in a time of climate change. It is not known if the industry was individually invented or the product of experimentation over hundreds of thousands of years. A 366 x 427 × 30 centimeter (12 × 14 × 1 foot) circle constructed of volcanic rock were found in 1962 in Olduvai Gorge. Rocks piled 15-23 centimeters 6-9 inches) high in 61-76 centimeter (2-2.5 foot) intervals were suggested by Mary Leakey to support poles that supported a windbreak or hut, since apomorphic tribes construct similar walls to build temporary shelter, using branches as poles and grasses and animal hide as a screen. This is 1.75 million years old, being the oldest architecture, possibly being made by late-surviving *H. habilis* of *Homo ergaster*.

## Synonyms

* *Australopithecus habilis*
* *H. microcranous*
* *H. guatengensis*
* *H. olduvaiensis*
* *H. habalis* (lapsus)
* *Australopithecus africanus habilis*
* *H. sapiens habilis*
* *H. erectus habilis*
* *H. erectus olduvaiensis*

## Subspecies

### Reassigned Subspecies

* *H. h. habilis*
* *H. h. platyops*
* *H. h. rudolfensis*
* *H. h. guatengensis*
* *H. h. sediba*

## Notable Specimens

* AL 666: An *H. cf. habilis*, consisting of a maxilla from Hadar that is 2.33 million years old. It was once one of the primary contenders to represent a novel species dubbed *H. guatengensis*, but the species has since fallen into disuse as a catch-all taxon.
* SK 847: A fragmented cranium sometimes assigned to this species, an australopithecine or as a paratype for *Homo guatengensis*, the former being a wastebasket that has been disused. It is debated whether the specimen is a composite of 3 elements, which may explain why up to 5 hominin species have been proposed to support this specimen. Many features (a short and narrow face, a large brow, a sharp-sloping frontal, delicate cheekbones, a rounded and forward-projecting nasal, a defined supratoral sulcus, moderate constriction behind the eyes, a short palate and small temporomandibular joint) line with *Homo*.
* Stw 75-79: Teeth that just barely fall into the variation of *H. habilis*, but were used as paratypes for *H. guatengensis*. They also bear similarities to *H. erectus* and australopithecines.

## References

* https://en.wikipedia.org/wiki/Homo\_habilis
* https://en.wikipedia.org/wiki/Homo\_gautengensis
* https://www.researchgate.net/publication/282758082\_Early\_Pleistocene\_Homo
* https://www.sciencedirect.com/science/article/abs/pii/S0018442X10000727
* https://en.wikipedia.org/wiki/SK\_847
* Smith, Dwight and Mangiacopra, Gary. (2007). The Hobbits of Flores: A New Genus of Hominid – *Parahomo*. In: Heinselmann, Craig (ed.). *Elementum Bestia: Being an Examination of Unknown Animals of the Air, Earth, Fire and Water*. CRYPTO. 265 pp.
* https://books.google.ca/books?id=440TmWXToLAC&dq=%22proanthropus%22&source=gbs\_navlinks\_s