Homo habilis

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Homo habilis

• The Discovery of Handy Man

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The Discovery of Handyman Homo habilis

• In the summer of 1959, just weeks before the
  discovery of the Zinj cranium (P. boisei), a
  left mandibular fragments with M3 and isolates
  lower premolar were found about 8 ft above the
  basal lave at site MK, Bed I, Olduvai.
• These teeth (OH 4) were smack, narrow, and
  elongated.
• However, in the excitement over the discovery of
  the Zinj cranium a few weeks later, a detailed
  analysis of the MK teeth was postponed.

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• The following year some fragmentary postcranial
  (tibia and fibula-OH 35), calvarial, and dental
  (OH 6) remains of another small-toothed hominid
  were found at the same site (FLK) 2 that had
  yielded the massive-toothed type specimen of A.
  boisei (OH 5).
• The size and proportions of these smaller teeth
  clearly ruled out that this was an example of
  sexual dimorphism.

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• Later that same year, Louis and Mary Leakeys
  eldest son, Jonathan, discovered additional
  remains from a nearby occupational site, or
  living floor (FLK NN).
• These consisted of the greater part of a juvenile
  mandible with teeth, an isolated upper molar,
  large parts of two juvenile parietal bone, and a
  number of wrist, hand, and finger bones.
• All of these specimens were designated OH 7.

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• This hominizing trend was not confined to the
  teeth, however.
• Even though the parietals belonged to a juvenile,
  they were far bigger than any australopithecine
  parietals thus far described.
• Based on their size and shape, endocranial
  capacity was estimated at 642-723 cc in this
  individual, which is greater than in any
  australopithecine.

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• Thus, the same creature which showed hominizing
  tendencies in its teeth also showed a more
  hominized brain-size.
• Over the next few years, several other specimens
  were found (for example, OH 13,16) and in 1964
  these became the basis for the description of a
  new species of Homo that was formally named H.
  habilis.
• The type of the new species, i.e., the specimen
  that serves as the standard for the taxon, became
  the OH 7 sample mentioned above.

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• Other specimens attributed to H. habilis included
  the skull fragments and teeth (OH 4 and 6), part
  of an adult foot (OH 8), an incomplete cranium of
  an adolescent (OH 13), a collection of juvenile
  cranial pieces (OH 14), and the fragmented
  cranial vault and dentition (OH 16) of a young
  adult (8).
• The name habilis was suggested to Leakey,
  Tobias, and Napier by Raymond Dart and in Latin
  means handy, skillful, able.
• The best known specimens from Olduvai include
• OH 7 (known as Jonny's Child, after its
  discoverer, Jonathan Leakey),
• OH 13 ("Cinderella")
• OH 16 ("George")
• OH 24 ("Twiggy").

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• Some traditions die hard, and many
  anthropologists were not amused by the naming of
  a new species of Homo.
• While two of its describers proposed early on
  that H. habilis was both a phenetic and phyletic
  link between Australopithecus and H. erectus,
  this view was not universally shared.
• Critics raised doubts on several fronts,
  reflecting both the prevailing paradigms and
  biases of the day

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• it was believed that the morphological distance
  between A. africanus and H. erectus was too
  slight to accommodate another species between
  them.
• brain enlargement was accepted as a preeminent
  hallmark of Homo thus, hominids with brain sizes
  smaller than those of H. erectus could not be
  called Homo
• the definition of the genus Homo was held to be
  immutable and sacrosanct, and some critics were
  uncomfortable that Leakey, Tobias, and Napier
  would broaden it to accommodate habilis
• behavioral considerations, such as stone-tool
  culture, were considered irrelevant to the
  definition and diagnoses of hominid species

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• The senior author of the new species, Louis
  Leakey, took another tack altogether.
• He concluded that several features of cranial
  shape shared by H. habilis and H. sapiens were
  not found in H. erectus, and therefore H. habilis
  should not be regarded as a stage between A.
  africanus and H. erectus, but rather as a form
  directly ancestral to H. sapiens !
• By the end of the 1970s, many anthropologists
  came to recognize the distinctiveness of H.
  habilis, not only from Olduvai but also from
  other sites in East Africa like Lake Turkana and
  Omo and possibly from locations in South Africa
  (Sterkfontein).

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Morphological Features of Homo habilis

• In general, the cranium of H. habilis is more
  gracile than that of Australopithecus,
  particularly in its less well developed muscular
  crests.
• Cranial capacity averages about 650 cc and
  endocranial casts reveal the first
  paleoneurological evidence for Brocas area, the
  speech area in the left cerebral cortex.
• Average cranial capacities
• 413 cc for A. afarensi
• 441 cc for A. africanus
• 530 cc for A. robustus
• 515 cc for A. boisei.

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• Facial heights and breadths are reduced relative
  to those in Australopithecus
• In general, maxillae and mandibles are smaller
  than in Australopithecus and are within the size
  range of H. erectus and H. sapiens.
• The sagittal curvature of the parietal bone
  varies from slight (within the hominine range) to
  moderate (within the australopithecine range) and
  the curvature of the occipital bone is less than
  in Australopithecus or H. erectus, and within the
  range of H. sapiens

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• Regarding the dentition
• The canines are proportionately large relative to
  the premolars.
• The premolars and molars are within or below the
  size range found in A. africanus, while the
  incisors are relatively larger.
• There is a marked tendency toward (side-to-side)
  narrowing and (front-to-back) elongation of most
  teeth, especially the lower premolars and molars

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• H. habilis shows an interesting mosaic of
  australopithecine and Homo like postcranial
  features.
• For example, the foot is humanlike in terms of
  metatarsal robustness and in having a well-marked
  longitudinal and transverse arch and a
  nonopposable hallux.
• The middle phalanges of the hand are somewhat
  apelike in being robust and curved with
  well-marked insertions for powerful muscles of
  finger flexion however, the overall length and
  morphology of the distal phalanges are similar to
  those of modern humans and, most importantly, the
  thumb joint, or carpometacarpaljoint, is
  distinctly humanlike
• It would thus seem that H. habilis was bipedal
  but retained a hand capable of powerful grasping.

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Homo habilis One Species of Two?

• Two questions that paleoanthropologists must
  constantly grapple with are
• 1) How different do two fossils have to be in
  order to be considered different species?
• 2) How similar must two fossils be in order to be
  attributed to the same species?
• It has recently been argued that
  paleoanthropologists probably err on the side of
  underestimating the amount of taxonomic diversity
  in the hominid fossil record.
• Perhaps in partial reaction to this, there has
  recently been renewed interest in reevaluating
  the taxonomic homogeneity of the H. habilis
  hypodigm

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• Our whole concept of the taxon H. habilis is
  really based on the fossil material from Beds 1
  and II at Olduvai and there seems to be a slowly
  growing consensus that most, if not all, of this
  material is reasonably encompassed within a
  single species, the more important specimens
  being
• OH 7 (the type)
• OH 13 (cranial parts and mandible)
• OH 16 (badly fragmented cranium and mandibular
  dentition)
• OH 24 (crushed cranium)

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