early humans: meet the ancestors 2. archaeological evidence and the limits of knowledge
TRANSCRIPT
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Early Humans: Meet the Ancestors
2. Archaeological Evidence and the Limits of Knowledge
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Objectives
• Look at the scientific investigative tools
• Stratigraphy
• Archaeological dating methods
• Comparative Anatomy of Fossils
• DNA and Isotope analysis
• Artefact and Ecofact Evidence
• Consider the security of our interpretations.
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Charles Darwin
• Origin of Species, 1859
• The Descent of Man, 1871
• Cartoon from “The Hornet” satirical magazine 1871
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Stratigraphy
• Provides relative dating – separating the remote past into horizons of greater and lesser age.
• Boxgrove, England
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Fauna Assemblages – Environmental Dating
• Boxgrove excavation era of strata indicated by animal bone assemblages
• Extinct rhinocerous,
Stephanorhinus hundsheimensis• Period when Britain had a climate
like modern Africa• Sites can be given sequence
relative to each other but not a date by this method.
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Radio Carbon Dating
• Invented c. 1950
• Based on the principle that C14 decays at a predictable rate
• Age calculation made by examining ratio of C14 and C12
• Relatively short half life c. 5740 years makes it accurate, but limits its range to about the last 40,000 years
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Lascaux, S France
• Accelerator Mass Spectroscopy – very small samples.
• C14 dating of cave painting, targeting carbon based pigments
• Images date to 30-10 kya• Some images refreshed
over thousands of years
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Potassium - Argon Dating
• Less accurate but much greater dating range – suitable for the earliest hominids
• Used to date layers of volcanic rock
• Noble gas Argon 40 released when rock molten
• Any Argon 40 present must have derived from Radio Decay of Potassium
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Laetoli, Early Hominid FootprintsVolcanic ash Potassium – Argon suggests 3.6 mya
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Uranium Series Dating
• Based on ratios between radio active Uranium isotopes and daughter products
• Uranium products are soluble in water.
• Thorium and Protractium products are insoluble in water.
• Calcareous deposits like limestone therefore start their existence with no Thorium or Protractium present.
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Uranium 238 Series
• Uranium 238 4.51 billion years
• Uranium 234 250,000 years
• Thorium 230 75,200 years
• Radium 226 1620 years
• Radon 222 3.83 days
• Lead 210 22 years
• Polonium 210 138 days
• Lead 206 stable
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Uranium 235 Series
• Uranium 235 713 million years
• Protractium 231 32,400 years
• Thorium 227 18.6 days
• Radium 223 11.1 days
• Lead 207 stable
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Vartop Cave, Romania
• Limestone cave Neanderthal occupation dated to 62kya to 97kya by U-series.
• Footprints Suggests an individual 1.46 m tall
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Cave Art Creswell Crags, Derbyshire
• Engraving Church Hole Creswell Crags
• U-series sampling of flowstone suggests pre- 12,800 BP
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Equilibrium Level
As levels of Thorium 230 increase rate at which it is destroyed approaches rate at which Thorium 230 is created by decay of Uranium 234.
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Comparative Anatomy of Fossils
• Comparison of cranial capacity
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Incompleteness
• Australopithecus Afarensis• Best specimen “Lucy”• Only 40 % complete• No formal burials from this
period. • Most bodies dismembered and
scattered by scavengers
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Turkana Boy
• H. erectus, 1.5 mya• Very narrow spinal column• Lacked fine control of diaphragm• Implications for speach• Other specimens fall with range
of modern humans• Might be an individual with
genetic defect.
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New Species or or Diseased
Individual
• Recent discovery of a new “hobbit” species contested
• H. floresiensis skull compared to modern human with the genetic disorder microcephaly.
• H. floresiensis frontal and temporal lobes highly developed
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Dimorphism in Australopithecine
• Suggested Australopithecine dimorphism as compared to modern humans
• Hominids of different sizes now thought to represent different contemporary species
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Ancient DNA
• Cheddar Gorge• Late Palaeolithic skull
1911• DNA recovered 1990’s• Adrian Targett –
descendant living few miles from find site
• Fears of contamination from modern DNA
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Age Estimation
• Tooth Eruption can give age at death in modern humans very accurately
• Age can also be estimated from the state of fusion of bones of the skull and limbs
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Errors in estimating age
• Australopithecene infant “Taung’s Child”
• Age by comparison with humans 7 years
• Age by comparison with chimps 3 years
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Comparative Anatomy - Teeth
• Nakalipithecus nakayamei jaw, Kenya, c 10mya• Homo erectus c. 1 mya• Broad grinding teeth indicate a fibrous plant diet, smaller
teeth of H. erectus indicate an omnivore's diet – high value foods like fruit and meat.
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Isotopes and Diet• Fractionation of stable
isotopes can idicate the origin of food sources.
• Ratios of C13 and C12 different for terrestrial and marine diets
• Mesolithic shell midden with human remains, Oronsay, Inner Hebrides
• Suggest protein almost entirely from fish, shellfish and marine mammals
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• Butchered animal bone, Boxgrove
• Homebase site – resources brought back to a central base.
• Sequence of cuts and knaw marks suggests human kill later scavenged by other large predators,
Assessing Prey Species
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Tool Use
• Modern chimps demonstrating tool use.• Baringo Basin tools, Kenya 2.6 mya• Earlier tools almost certainly being used but
impossible to distinguish from naturally broken material
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Inorganic Artefacts
• Clacton-on-Sea spear• Sharpened and fire
hardened shaft• Earliest wooden artefact,
290 kya• Associated with Homo
heidelbergensis.• Earlier artefacts simply
have not survived.
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Problems
• Interpretation rests on very partial survival of evidence.
• Measuring errors – complex procedures to measure very small differences in composition
• Sampling errors – contamination • Most interesting statements rest on chains of
inference• All data is subject to a degree of doubt
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Piltdown Man Hoax• Discovered 1908 gravel pit
East Sussex by museum Charles Dawson
• Published in the Journal of the Geological Society 1912, named Eoanthropus dawsoni
• Exposed by fluoride absorption test 1949, published 1953 in “Time”
• Medieval human skull Orang-utan jaw and chimpanzee teeth