IN SEARCH OF HUMAN ORIGINS

Jinsha Museum in Chengdu, southwest China's Sichuan province.

What are the features of the primate skeleton, and how can knowledge of them help us identify fossil remains?

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.

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.

FOSSILS

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.

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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.

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.

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.

Archaeological Excavation

Excavation is the technique used to uncover buried remains from the past. Buried materials are usually more abundant

and better preserved than those found on the surface.

Excavation is often essential to obtain more information about the past.

Excavations are conducted to answer specific questions framed by the archaeologist.

Archaeological Excavation

Selecting sites for excavation involves several factors. Sites threatened by modern construction

are often good candidates for excavation. Sites are also chosen because they are well-

preserved or contain information that will aid the understanding of a particular region or time.

The choice of a site is often based upon the results of a survey.

Archaeological Excavation

Creating maps and grids during excavation is essential. Accurate mapping of layers and artifacts is

the key to the proper recording of information.

A grid is marked out across the surface of a site prior to excavation.

Reference points need to be established. Today, a total station is used to

electronically map sites.

Archaeological Excavation

Vertical excavations take the form of pits or trenches placed across a site. The stratigraphy, or layers, reveal how the

site was formed and how materials accumulated.

The bottom layer is typically the oldest. Evaluation of a stratigraphic sequence

involves distinguishing between natural and human activities.

Assessment of the layers allows for the interpretation of the history of the deposits.

Archaeological Excavation

Horizontal, or area, excavations often follow vertical excavations and expose large areas of ground. Area excavations are intended to recover

information on site arrangement and structures.

Actual prehistoric living floors may be exposed.

As layers are removed, information about each one is analyzed and recorded.

Analysis of Archaeological Materials Fieldwork yields portable objects altered by

human activities, called artifacts. Artifacts must be cleaned and recorded. A catalog description of each artifact

includes many pieces of information, such as form, technology, and style.

A description could include a drawing or picture.

Classifying the artifacts into specific types can create order.