Human EvolutionThe beginning: 10 million years ago in Africa

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

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 don’t know– Carrying babies?

– Making tools?

– Thermodymics?

– Wading along shorelines?

– Looking for predators?

– More efficient movement?

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

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

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?

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-1970’s by Donald Johanson and dated to around 3.3 mybp, similar date for “Lucy’s 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

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

Earliest hominins: Australopiths

• Lucy bones – unquestionably bipedal. Some adaptations for tree-dwelling present. Small 3-4 feet in stature. High sexual dimorphism. Probably didn’t run very well. Ate fruits, nuts, insects, small USOs, amounts of meat. Was prey as much as predator.

Earliest hominins: Australopiths

• Dart’s 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?

Earliest hominins: Australopiths

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

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)

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.

Early Homo

• Homo habilis: Unearthed 1960’s 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: 1970’s Richard Leakey. Brain size 750cc, but with more primitive looking face. Both dated to around 2.3-2.0 mybp

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

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

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

Knapping apes

• Kanzi knapping studies• Produces “oldowan-like” tools, but not using percussion

technique• Less power; less precision and selectivity

• 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.

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.

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

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

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

A tale of two species: African ergaster and Asian erectus

• Asian erectusremained 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 sapiensH. heidelbergensis very likely migrated extensively throughout Europe, east Asia, and possibly Africa. Probably the first true big-game hunter.

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.

Summary of Hominin Species

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.

Evolving mental capacities

• Boxgrove debitage (400kybp)

• Berekhat Ram (230kybp)

• Levallois “prepared core” technique (300kybp

• Pigment use (300kybp)

• Control of fire (300kybp)

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.