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
Earliest hominins: pre-Australopiths • Orrorin tugenenis “original man” in the local Tugen language. February 2001, French researcher Brigitte Senut, a few teeth and bone scraps in the Tugen hills of Kenya, dated to about 6mybp
Earliest hominins: pre-Australopiths • Ardipithecus kadabba found in the Middle Awash region of Ethiopia, dated to around 5.5 mybp • There is still some discussion as to whether kadabba is a separate species or a subspecies of the later-emerging Ardipithecus ramidus whose remains are dated to between 5-4.4 mybp
Earliest hominins: Australopiths • Australopithecus anamensis, first uncovered in 1995 in northern Kenya and dated to between 4.2 and 3.9 mybp. • Australopithecus afarensis (Lucy) found in the mid-1970’s by Donald Johanson and dated to around 3.3 mybp • Australopithecus africanus, Tung child found by Raymond Dart of the University of Witwatersrand in South Africa, 1922. Dated as somewhat more recent than Lucy
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. At fruits, nuts, insects, small amounts of meat. Was prey as much as predator.
Earliest hominins: Australopiths • Dart’s Taung child, killed by predator?
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. • 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).
Percussion technique requires motor control beyond that of nonhuman apes. Some advance in planning perceptual motor skills. 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.
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.
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 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.
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.
Acheulean Tool kit: emerges about 1.4mybp • 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.
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.
Middle Paleolithic or Middle Stone Age: 250,000 – 35,000 ybp • Emergence of two new species (possibly both descended from Homo heidelbergensis: Homo neanderthalensis (Neanderthals in Europe), and Homo sapiens sapiens (AMH in Africa). • Levant event: First (failed) excursion of AMH out of Africa
Brain Evolution • Increasing brain volume and EQ over time • Climatic explanation? Vrba turn-over pulse hypo; early brain expansion but not later • Ecological hypothesis: necessary but not sufficient; tools only roughly correspond to brain expansion • Social complexity: evidence of later Homo as superpredator
Toba eruption: 73,000 ybpPopulation bottleneck: 1-5,000 breeding females
Tsodilo Hills snake rock: first evidence of religion?Beads and body ornaments: evidence of trade networks? • Tsodilo Hills of Botswana. It was here in 2006 that University of Oslo archeologist Sheila Coulson discovered a ritually-modified snake-rock, dated to around 70,000 ybp (Minkel, 2006). The 6 meter long by 2 meter high boulder had a natural snake-like appearance that had been intentionally modified so that incoming natural light gave the impression of scales on its surface while firelight gave the impression of undulating movement. For Coulson, these modifications strongly suggested use of the site for consciousness altering rituals. The python plays an especially prominent role in San creation myths and Tsodilo hills are thought to be sacred.
Paul Mellars (2006) • Cites genetic evidence to argue for a “relative” population explosion among specific human groups around 80-60,000 ybp in Africa. • Mellars, P. (2006). Why did modern human populations disperse from Africa ca. 60,000 years ago? A new model. Proceedings of the National Academy of Science, 103, 9381-9386.
Modern Cognition: Cave art, abstract artifacts, religious/symbolic imagery