Human Evolution The beginning: 10 million years ago in Africa

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Human EvolutionThe beginning 10 million years
ago in Africa

• Climatic change. Getting drier. Unbroken tropical
  forests becoming a patchwork of woodland and
  savanna.

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The split

• Sometime around 7 mybp east African primates
  began on an evolutionary path distinct from
  central and west African primates.
• West was more densely wooded. East less so, more
  open. East African primates went bipedal. Why? We
  dont know
• Carrying babies?
• Making tools?
• Thermodymics?
• Wading along shorelines?
• Looking for predators?
• More efficient movement?

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Earliest hominins pre-Australopiths

• Sahelanthropus tchadensis. (Toumai, hope of
  life in Goran). A single skull, jaw fragments,
  several teeth, unearthed in 2002 by Michael
  Brunet, dated to about 6.5 mybp Found in Chad,
  central Africa?
• Forward position of foramen magnum suggest
  bipedalism

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Earliest hominins pre-Australopiths

• Orrorin tugenenis original man in the local
  Tugen language. February 2001, French researcher
  Brigitte Senut, a few teeth and limb bone
  fragments in the Tugen hills of Kenya, dated to
  about 6mybp
• Femur (valgus) angle suggests bipedalism

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Earliest hominins pre-Australopiths

• Ardipithecus kadabba found in the Middle Awash
  region of Ethiopia, dated to around 5.5 mybp
• Ardipithecus ramidus (Ardi) remains are dated to
  between 5-4.4 mybp forest-dwelling, bipedal, but
  at home in trees as well. No evidence of
  knuckle-walking is this derived feature in great
  apes?
• Contros
• Are kadabba and ramidus related?
• Are kadabba, orrorin, and sahelanthropus related?
• Ardi appears to have low sexual size dimorphism,
  but australopiths have traditionally been thought
  of as highly dimorphic species?
• Is Ardi the only one likely to be ancestral to
  Homo?

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Earliest hominins Australopiths

• Australopithecus anamensis, first uncovered in
  1995 in northern Kenya and dated to between 4.2
  and 3.9 mybp. Descended from knuckle-walker
  (terrestrial before bipedal? contrast with Ardi.
• Australopithecus afarensis (Lucy) found in the
  mid-1970s by Donald Johanson and dated to around
  3.3 mybp, similar date for Lucys child found
  at Dikika, Ethiopia, est. 3yrs of age.
• Australopithecus africanus, Tung child found by
  Raymond Dart of the University of Witwatersrand
  in South Africa, 1922. Dated as somewhat more
  recent than Lucy

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Australopiths

• Australopithecus sediba
• Discovered in 2008 by Matthew Berger (9 year old
  son of Lee Berger). Not described until 2010.
  South Africa
• Later australopith showing a mosaic of
  australopith (teeth, limbs, upper chest) and homo
  features (lower chest, skull, face, pre-molars)
• A species at the transition point between
  Australopiths and Homo?
• Dated to 2-1.5 mybp

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Earliest hominins Australopiths

• Lucy bones unquestionably bipedal. Some
  adaptations for tree-dwelling present. Small 3-4
  feet in stature. High sexual dimorphism. Probably
  didnt run very well. Ate fruits, nuts, insects,
  small USOs, amounts of meat. Was prey as much as
  predator.

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Earliest hominins Australopiths

• Darts Taung child, killed by predator? Dated at
  about 2.5mybp, est. 4yrs.
• Period of nutritional stress at 2.5yrs, possible
  early weaning age compared to apes evidence of
  cooperative breeding, care of young?

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Earliest hominins Australopiths

• The pitted pattern of Laetoli feet, about 3.5
  mybp.

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Earliest hominins Australopiths

• Two general types
• Gracile Thinner boned, less powerful jaws,
  probably ate more fruits, insects, etc. (ex.
  Africanus, afarensis)
• Robust thicker boned, more powerful jaws, ridge
  crest on cranium, flatter teeth, seed-crusher?,
  fibrous vegetable material (probably not human
  ancestor ex Australopithicus or Paranthropus
  boisei and A. or P. aethiopicus)

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Earliest hominins Australopiths

• Summary Time period 5-1mybp, robust later than
  gracile. Robusts may have made stone tools, but
  little evidence. High sexual dimorphism, male
  male competition. Small family female bonded
  groups, single male. Bipedal but well adapted to
  trees. Forest, waterside dweller. Chimp-size
  brain, robust a little larger. Probably
  restricted to Africa. Bipedal apes.

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Early Homo

• Homo habilis Unearthed 1960s Louis Leakey.
  Olduvai Gorge in northern Tanzania. Larger brain
  size (640cc note chimps are about 400cc).
  Evidence of simple stone tools found also
  (Oldowan tools).
• Homo rudolfensis 1970s Richard Leakey. Brain
  size 750cc, but with more primitive looking face.
  Both dated to around 2.3-2.0 mybp

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The Oldowan tool kit

• Simple stone tools made by striking a hammer
  stone against a core to make a shape flake (cores
  may also have been used occasionally as tools).
  2.6mybp

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Hand/Brain and tool manufacture

• Pad to side grip thumb to side of index finger
• Three jawed chuck grip thumb, index, middle
  finger (baseball grip)
• Five jawed cradle thumb against four fingers
• Lucy could use these grips, apes generally
  cannot. Pounding, digging (USOs), throwing.
  Oldowan tools probably not, but maybe robusts
  later.
• What Lucy could not do
• Oblique power grip fourth and fifth fingers in
  ulnar opposition to thumb, used for holding and
  swinging clubs and hammers

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Hand/Brain and tool manufacture

• Pet scans of Oldowan knapping visual-motor
  coordination
• Primary motor cortex
• Somatosensory cortex
• Dorsal visual pathway (occipital/superior
  partietal)
• Cerrebellum
• Little frontal lobe activation

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Knapping apes

• Kanzi knapping studies
• Produces oldowan-like tools, but not using
  percussion technique
• Less power less precision and selectivity

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• Percussion technique requires motor control
  beyond that of nonhuman apes. Some advance in
  planning perceptual motor skills.
• Some evidence of adjustment in ongoing flaking
  process (Lokalalei site, northern Keyna)
• Probably not a big cognitive advance.

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Homo erectus/ergaster

• Nariokotome boy 1984 Richard Leakey. Near
  complete skeleton of 12 year old boy, west of
  Lake Turkana in northern Kenya, dated to around
  1.4mybp.

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Nariokotome

• 1984 the bones of an 11 ½ year old boy were found
  under a tree along a dry stream channel west of
  Lake Turkana

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Homo erectus/ergaster

• Erectus/ergaster probably emerged around 1.8mybp
  in Africa.
• Evidence of a quick expansion out of Africa into
  East Asia (1.7mybp) and Southeast Asia (1.5mybp).
  
• Some argue that Asia derivative should be
  erectus and African should be ergaster.
• Fully committed biped.
• Much larger brain NB 900cc
• Much lower sexual size dimorphism (in human
  range)
• Larger, more cooperative social groups
• More meat in diet
• Use, maybe control of fire
• Around 1.4mybp emergence of new tool
  technology Acheulen tools.

The earliest evidence for controlled use of fire
comes from the 790,000-year-old site of Gesher
Benot Ya'aquov, Israel, as depicted in this
illustration
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A tale of two species African ergaster and Asian
erectus

• African ergaster
• Ergaster migrated out of African almost as soon
  as it emerged.
• The ergaster that remained in Africa either (a)
  slowly evolved into modern Homo sapiens or (b)
  went extinct, leaving Africa to be re-colonized
  by descendants of Asian erectus who eventually
  evolved into modern Homo sapiens

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A tale of two species African ergaster and Asian
erectus

• Asian erectus
• remained in extreme southeast Asia until as
  recently as 20,000 ybp (Homo florensiensis the
  hobbit)
• Evolved into Homo heidelbergensis in Eurasia
  (500,000ybp) who eventually gave rise to
  Neanderthals and quite possibly Homo sapiens
• H. heidelbergensis very likely migrated
  extensively throughout Europe, east Asia, and
  possibly Africa. Probably the first true big-game
  hunter.

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Homo heidelbergensis

• 350,000 to 500,000 YA. The Homo heidelbergensis
  Skull Atapuerca 5 was discovered in Spain in 1992
  by Juan-Luis Arsuaga, in the fossil-rich caves of
  Sima de los Huesos (Bone Pit), Sierra de
  Atapuerca, This site has thus far yielded over
  5000 fossil hominid remains. Although somewhat
  smaller than other H. heidelbergensis, this
  individual is considered among the most complete
  premodern skulls ever found. The cranial capacity
  is 1125 cc.

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Summary of Hominin Species
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Acheulean Tool kit emerges about 1.4-7mybp

• Larger tools, more specialized, exemplified by
  the hand axe
• Later versions of hand axe (.5mybp) suggest an
  image to guide tool creation, attention to
  symmetry and shape. Some may not have been
  strictly utilitarian.

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Evolving mental capacities

• Boxgrove debitage (400kybp)
• Berekhat Ram (230kybp)
• Levallois prepared core technique (300kybp
• Pigment use (300kybp)
• Control of fire (300kybp)

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Composite tools 300,000 ybp

• Tools with multiple components (1) point,
  affixed to a (2) shaft, using a (3) binder.
  Extended construction processing possibly
  requiring the same type of sequential motor
  planning necessary for language.