IN SEARCH OF HUMAN ORIGINS

 What are the features of the primate skeleton, and how can knowledge of them help us identify fossil remains?  Great Rift Valley  How do we locate, recover, and date fossil remains?  How are fossils formed, and what affects the condition of the fossils we find?  What can we learn about our past from new technologies in the study of genetics?

Osteology  Bones: The Primate Skeleton  When we look at a skeleton, it’s easy to imagine the bones as something separate from the muscles, nerves, blood vessels, and other soft tissues of the body. But, in fact, they all develop together and are adapted to function together.  Definition The study of the skeleton.

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Sexual Dimorphism  One of the more obvious and important things we can tell about a human skeleton is its sex. Humans belong to a species that exhibits sexual dimorphism, notably physical differences between the sexes that are not related to reproductive traits.  Definition: Physical differences between the sexes of a species not related to reproductive features.

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FOSSILS  Old Bones: Locating, Recovering and Dating fossils  A fossil is a priceless treasure, and finding one is an uncommon event.

Studying the Human Past © 2010 The McGraw-Hill Companies, Inc. All Rights Reserved 10  Old Bones: Locating, Recovering and Dating fossils  A fossil is a priceless treasure, and finding one is an uncommon event.

How Fossils get to be Fossils  The conditions under which an organisms, or some of its parts, can be preserved are quite specific.  A fossil reveals more than just the type of organism it once belonged to. A fossil also contains clues as to how the animal died and what happened to it after its death.  Definition: Petrified  Turned to stone. .

TECHNIQUE  Superposition  The principle of stratigraphy that, barring disturbances, more recent layers are superimposed over older ones.  Relative Dating Technique  A dating method that indicates the age of one item in comparison to another.  Biostratigraphy  The study of fossils in their stratigraphic context. Used as a relative dating technique.  Absolute Dating Technique  Dating methods that give specific ages, years, or ranges of years for objects or sites.  Chronometric Techniques  Another name for absolute dating techniques.  Radiometric  Referring to the decay rate of a radioactive substance.

DATING TECHNIQUES  Radiocarbon Dating  A radiometric dating technique using the decay rate of a radioactive form of carbon found in organic remains.  Half-life  The time needed for one-half of a given amount of a radioactive substance to decay.  Potassium/argon (K/Ar) Dating  A radiometric dating technique using the rate at which radioactive potassium, found in volcanic rock, decays into stable argon gas.  Argon/argon Dating  A radiometric dating technique that uses the decay of radioactive argon into stable argon gas. Can be used to date smaller samples and volcanic rock with greater accuracy than K/Ar dating.  Electron Spin Resonance (ESR) Dating  An absolute dating technique that measures the number of electrons excited to higher energy levels by natural radiation and trapped at those levels. Can be used to date tooth enamel, shells, corals, mineral cave deposits, and volcanic rock, but does not work well on bone.

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 Luminescence Dating  An absolute dating technique that measures trapped electrons by releasing their energy in the form of light. Can be used to date fired clay, pottery, and brick. It may have some application in soil dating.

Genes: New Windows to the Past  Two species may look very different, but their differences may be the result of extensive phenotypic effects of a very small number of genes, and the species may actually be quite closely related. Humans and chimps are an example. We are 98 percent genetically identical.

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 Summary  Although data from fossils is millions of years old, we may still use scientific methodology to interpret them.  We understand how fossils are formed and what their specific condition can tell us about how the organism died and became part of the fossil record.  Combining the preceding techniques with new methods from genetics, we have been able to piece together a tentative family tree of the hominids and related primates.