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Week 12
Chimpanzees
Dating things
Intro to Human Origins
Chimpanzees
(Pan troglodytes)
Chimpanzees
  Chimpanzees are perhaps the best
known of all nonhuman primates.
  Most of us experience captive or
trained chimpanzee behavior and
consider it as being “just like
human.”
  There is a difference between trained
behavior and conscience choicedriven behavior
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  Chimpanzees are found in
Africa in rainforests or in
mixed forest-savanna
environments.
  Like gorillas, they are
knuckle-walkers with longer
arms than legs, but they are
more agile than gorillas.
  They are both terrestrial and
arboreal.
  Their diet consists of fruit,
leaves, seeds, nuts, insects,
and meat (small animals like
monkeys).
Chimpanzees
  Chimpanzees live in large
communities of 50 or more
individuals.
  Their social structure
constantly changes.
  They recognize and interact
with others in thee group.
  The most important social
behaviors revolve around
mother and infant.
  Adult males are generally
dominant.
Chimpanzees
  Fission-fusion arrangement
Fission-fusion society
  Multiple females and males live together in one
group
  When resources are abundant, group stays
together
  When resources are scarce, parties divided by sex
  Males create territories based on kinship
  More complex inter-sex relationships
  Teasing, Laughter, Embraces, Display
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Bonobos (Pan paniscus)
  Bonobos are the least
well known of the African
apes.
  They are closely related
to the chimpanzee, and
commonly considered a
separate species of
chimpanzee known as
“pygmy chimpanzee.”
  They are unique to a
restricted rainforest
region of Zaire, central
Africa.
Bonobos
  They eat a leaf and plant
diet.
  Bonobos are distinguished
from chimpanzees by their
relatively longer legs,
narrower chest, and higher
center of gravity.
  Their forehead and face are
also shaped differently.
  They can walk upright more
easily than other apes.
  It has been suggested that
the first hominoids may have
been quite similar in many
ways.
Bonobos
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  Bonobos live in large
multimale / multifemale
groups like chimpanzees
  Strongest social bonds exist
between adult females.
  Bonobos are known to
practice polyandry
  Females withhold sex from
males in return for less
aggressive behavior
Bonobos
Dating the Past
  Our past can be revealed
from clues accumulated
over time. The fossil record
provides us with bits and
pieces of a small
proportion of living
organisms that have lied
and died in the past.
  In order to use this
information, we need to be
able to determine time
Dating Terminology
•  Relative Dating –
Placing events in
chronological order
but without assigning
numerical values.
•  Example: Julius
Caesar died before
today’s class.
•  This was the only way
anthropologists
measured time in
prehistory until the
20th century.
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Dating Terminology
•  Absolute Dating –
Giving a calendar date to
an event or events
•  Example: Julius Caesar
died on March 15, 44 B.C.
Today’s class occurred on
A.D. June 24, 2011.
•  Calendar dates use:
▫  BC/AD
▫  BCE – before common
era
▫  BP (bp) before present
  (1950)
Flourine Dating
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Relative Dating Methods
•  Fluorine Dating measures the accumulation of
fluorine levels in bone.
▫  The greater the amount of fluorine in bones from
the same area, the older they are
Pildown Man
Human skull
Orangutan jaw
Relative Dating Methods
•  Stratigraphy makes use of the geological process
of superposition, the cumulative buildup over
time of the earth’s surface.
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Absolute
Dating
"
The Target Event is
the event in which
we are interested. "
E.g. – when did
these two hominids
sit down to eat their
dinner?"
"  
The Dated Event is the event that a technique
actually provides a date for."
"
"
E.g. – when did the dirt surrounding their bodies
fuse into rock? "
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Target event vs. Dated event"
There can be (and often is) an unknown and
significant time-span between these two events. "
"  
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Absolute Dating
•  Use constant physical and chemical processes to
determine exact dates, subject to statistical
variation.
•  Many techniques are useful for archaeology by not
paleoanthropology
▫  Carbon-14 dating is only useful for sites as old as
50,000 years.
▫  Dendrochronology goes back 7,000 years
•  But there are ways!
Potassium -39
Protons
(always 19)
Neutrons
(usually 20)
Electrons
99.9% of all Potassium
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Potassium -40
Protons
(always 19)
Neutrons
(21)
Electrons
< .1% of all Potassium
Electron capture
•  In order stabilize itself,
an unstable isotope may
break a neutron and
emit an electron (beta
decay)
▫  This is what a Geiger
counter measures
•  Alternatively, it may
combine an electron
and a proton to form a
new neutron
Argon-40
Protons
(always 18)
Neutrons
(22)
Electrons
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K/Ar Dating
•  We can use the decay of 40K to 40Ar to date the
age of rocks
•  Potassium is a common component in felsic
rocks (granite)
•  Argon is stable and insoluble, so it will stay in
the rocks until measured
•  The amount of Ar in a sample can tell us how old
the rock is
Half life of 40K
Half-life  1,248,000,000 years
2 Half-lives  2,496,000 years
40K
decay
1.2
2.4
4.8
Billions of years
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Fission Track Dating
•  Based on the idea that
as (other) radioactive
isotopes go through
beta decay (emitting
electrons)
•  These free electrons
leave damage marks,
or tracks, in crystals of
rocks
Electron Spin Resonance
•  Alternatively, those
track-causing electrons
can become trapped in
the lattice of crystals
and affect the magnetic
field
•  By measuring changes
in the magnetic field, we
can determine how
much time has
transpired since mineral
formation
Reconstructing the Past
•  Interpreting Fossils
▫  Identifying Species mostly relies on an examination
of the morphology or structure of skeletal remains
to infer evolutionary relationships with other
specimens.
  Taphonomy: The study of what happens to plants
and animals after they die.
  Paleoecology: The study of ancient environments.
One example is palynology, the study of fossil pollen.
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Interpreting Behavior
•  Paleoanthropology employs a number of different
methods that allow inferences of behaviors to be
made.
▫  Stable Isotope Analysis is used on fossil remains to make
inferences about diet.
▫  Experimental Archaeology involves learning how to
make and use tools in the present in order to shed some
light on tool making and tool use in the ancient past.
▫  Nonhuman Primate Models for Behavior provides
insights into behavior during human evolution using
comparative data from studies on nonhuman primates.
How old are human beings?
  This can be answered in different ways:
  Roughly 200,000 years for those more or less
anatomically the same as living human beings.
  All large-brained humans, several hundred thousand
years.
  All members of the genus Homo, more than 2 million
years.
  All bipedal hominids, 6 million years.
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Humans and Apes
  The hominid line split from the African apes about 6-7
mya.
  They were bipedal and walked on the ground, but also
climbed in trees.
  By 3 mya, two distinct lines of hominid had evolved.
  One line led to several species known as “robusts.”
  The other line began to rely more and more on learned
behavior.
Fossil Evidence of Early
Hominid Evolution
  Evidence of fossil
remains resembles a
“bush” with many
branches rather than a
family “tree.”
  All species are
classified as hominids
because they show
direct or indirect
evidence of being
bipedal.
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Most early hominid species have been
found at sites in South Africa and East
Africa.
Great Rift Valley
Slide 41
Great Rift Valley
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Evolutionary Stages
  Stage 1: lived 6+ mya to 4.4 mya.
  Evidence is fragmentary, but indicates bipedalism.
Evolutionary Stages
  Stage 2: Australopithecines or “primitive
hominids” and lived between 4.3 to roughly 2
mya.
  They were small-brained bipeds with primitive ape
characteristics.
  Is highly diverse and represents a major split
Evolutionary Stages
  Stage 3: Development of the genus Homo.
  Appearance of modern characteristics.
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Genus Homo
Australopithecine
s
Early hominids
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