ANT203 Chapter 10 - Introduction to Physical Anthropology Textbook

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Maryam Nargolwalla

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CHAPTER 10: PALEOANTHROPOLOGY: RECONSTRUCTING EARLY HOMININ BEHAVIOR AND ECOLOGY I. Introduction a) Definite hominin fossil material has been found in Africa that dates to just after 5 mya. i) The hominin nature of these remains is indicated because of the way they behaved. ii) Hominin biocultural nature of human evolution, this chapter focuses in the methods scientists use to explore the secrets of early hominin behavior and ecology. II. Definition of a Hominin a) Hominin origins date to the end of the Miocene. b) Hominins have been variously defined as having: a large brain, bipedal locomotion, and/or tool-making behavior. i) It is clear that these characteristics did not evolve simultaneously. The phenomenon of different physiological systems evolving at different rates is called mosaic evolution. ii) Bipedal locomotion is the key indication that a fossil was a hominin. c) What’s in a name? we refer to members of the human family as hominins. i) Molecular evidence clearly shows that the great apes are not a monophyletic group. ii) Hominoid classification has been significantly revised adding two further taxonomic levels (subfamily and tribe). iii) There is very close evolutionary relationships between humans and African apes (particularly chimpanzees and bonobos) (1) The former term hominid has a quite different meaning in this revised classification referring to all great apes and humans. d) Biocultural evolution: the human capacity for culture i) The most distinctive feature of humans is our dependence on culture. (1) Human culture is an adaptive strategy that includes cognitive, political, social, and economic aspects as well as the capacity to make and use tools. ii) The earliest hominins did not regularly manufacture stone tools. (1) They probably had the tool-making capabilities of living chimpanzees. (a) Stone tools appear in the archaeological record about 2.6 mya. (2) By 7 to 6 mya, hominins had developed bipedalism and could carry and transport objects from place to place.. iii) The dynamics between neuronal reorganization, tool use, changing social organization, and communication form the core of biocultural evolution. III. The Strategy of Paleoanthropology a) Paleoanthropology, the study of ancient humans, is a multidisciplinary approach that includes geologists, archaeologists, physical anthropologists, and paleoecologists. i) The earliest artifact date back to 2.6 mya and were found in sites from the Gona and Bouri areas in northeastern Ethiopia. (1) Cut marks in bones found in Ethiopia extend this date to 3.4 mya. ii) Paleoanthropologists must synthesize information regarding: (1) Dating of the site. (2) The paleoecology of the site. (3) Any archaeological traces of behavior. (4) Any anatomical evidence from hominid remains. iii) The ultimate goal is to “flesh out” the hominids to produce a more complete and accurate understanding of human evolution. IV. Paleoanthropology in Action-Olduvai Gorge a) Olduvai Gorge, located on the eastern branch of the Great Rift Valley of Africa, has yielded an immense quantity of high-quality data on early hominid behavior. b) Olduvai has a well-documented sequence of geological, paleontological, archeological, and hominid remains that span the last 2 million years. i) The earliest hominid site dates to about 1.85 mya, and is accompanied by the Oldowan tool industry. ii) The most famous hominid fossil from Olduvai is probably the Zinjanthropus skull, discovered by Mary Leakey in 1959. V. Dating Methods a) The two types of dating methods are relative dating and chronometric, or absolute dating. i) One relative dating method is based on stratigraphy. (1) The law of superposition states that (in an undisturbed deposit) a lower layer is older than a higher layer. ii) Another relative dating method is fluorine analysis. (1) Groundwater contains fluorine, and the longer a bone is in a deposit; the more fluorine will accumulate during the fossilization process. (2) The fluorine method can only be used to compare bones found at the same location. iii) Chronometric methods are based on the phenomenon of the radioactive decay of unstable isotopes. (1) Depending on the half-life of the isotope used, the time range for this method varies from the age of the earth (billions of years) to less than 1,000 years. (a) Paleoanthropologists use the K/Ar method extensively to determine the age of volcanic deposits (and therefore the associated fossils) in East Africa. (i) The 40Ar/39Ar method can be used on smaller samples and provides more accurate results. (b) The C-14 method is used on organic materials and has a useful time-range of 75,000 to less than 1,000 years. (c) Thermoluminescence dates can be obtained from burnt flints. b) Applications of dating methods: examples from Olduvai i) Olduvai has several reliable K/Ar dates for the underlying basalt and the tuffs in Bed I, and the Zinj site has been dated to 1.79 + .3 mya (1) K/Ar dates must be cross-checked, since all dates have errors associated with them. (2) Another way of cross-checking is to use paleomagnetism. (a) With this technique, the orientation of magnetic sediments is checked to determine whether they were deposited during a period of normal or reversed magnetism. (3) Biostratigraphy, or faunal correlation, is another cross-check. (a) This technique matches faunal remains, such as pigs, elephants, rodents, and antelopes at the site in question with the known evolutionary sequences of the same faunal species. (4) Cross-checking with different methods lends confidence to the results because each method has a different source of error. VI. Excavations at Olduvai a) There are many hominin sites found at Olduvai. i) Mary Leakey excavated close to 20 of these sites. ii) There is much controversy regarding hominin activities at these sites (“campsites”). (1) These are general-purpose areas where hominins carried out daily activities. (2) The exact nature of the activities carried out at these
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