Transcript Introduction to Hominid Evolution

Studying the Human
Past
Where We’ve Been So Far
• Genetic forces that drive evolutionary change
– Process of inheritance
– Variation
– Natural selection
Laying the Foundation, Cont.
• Adaptations of the Non-human Primates
– Evolutionary trends/patterns in anatomy and
behavior
• Bigger bodies, bigger brains, increased social
complexity & cooperation, & increased intelligence
Our evolutionary past
• Is preserved in the form of fossils
Paleoanthropology & Osteology
• Study of human fossil record
– How old fossil is (dating techniques)
• To place in evolutionary context
– What kind of organism (human or nonhuman?)
– Ecological adaptations (diet & locomotion)
Fossilization
Only occurs under precise set of conditions:
Step One: Bones buried in sediment (sand,
mud, silt, gravel)
Step Two: Minerals from water & soils
replace protein material in the bones &
transform the bone into stone, preserving
its form
Step Three: Erosion, natural movement of
land exposes fossils
Step Four: Discovery
Biases in Fossil Record
• Fragmentary – bits & pieces of the
skeleton; less than 50 complete hominid
skeletons
• Over-representation of certain bones:
– Teeth, mandible (lower jaw), and bones of the
pelvis are most likely to be preserved (most
durable bones of the skeleton)
• Biases in interpretation
Questions about Fossil Remains
1. What kind of bones are they? (Part of the
skull or part of the post-cranial skeleton?)
2. Human or some other primate?
3. Male or female?
4. Age at time of death? (age of individual)
5. Age of bones themselves
6. Context in which bones were found
Human or non-human remains
• First trait to have developed that distinguishes
humans from other primates is BIPEDALISM
Skeletal Evidence for Bipedalism
Centralized foramen magnum (hole at base of skull
through which spine enters)
SKELETAL EVIDENCE FOR
BIPEDALISM
Rounded, short, bowl-shaped pelvis
Relative Limb Proportions: Longer, thicker, more
developed leg bones than arm bones
AnatomY OF BIPEDALisM
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Femur angles inward toward the knee
Big toe parallel to other toes
 Arch in foot bones
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MALE OR FEMALE?
• Scientists look for specific clues in the skeleton
• Focus is on pelvis & skull
Differences in the pelvis
• Male pelvis is narrower; illia are not as
splayed; arch in front is V shaped
• Female pelvis is wider, more robust, illia splay
outward, arch in front U shaped
Differences in the skull
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Male cranium is generally bigger
Female cranium:
has a square chin;
rounded chin;
less angle to jaw;
sharper angle to jaw;
larger mastoid bone;
smaller mastoid bone;
small bump at back;
no bump at back;
more sloping forehead;
more bulging forehead;
heavier browridges
fainter browridges
Clues from Teeth
Can obtain lots of information from teeth
What types of food were consumed
How they interacted with environment to acquire
food
For example, the patterns of wear on the teeth
suggest a diet of hard food items such as nuts,
seeds and roots requiring lots of chewing and
grinding
Other important information
• Age of bones/fossils
– Important to place in evolutionary time frame
– Many scientific methods to determine age
• Forensic information – What can we learn about the
individual?
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Stature
Age at time of death
Diseases or injuries evident
Strenuous physical activity
• This information is important to reconstruct the variation in
the population and the way of life of the individual
Major Turning Points in Human
Evolutionary History
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Development of bipedalism 6-7 mya
Stone tool manufacture 2.5 mya
Meat eating
Brain growth
Language
Culture (as primary means of adaptation)
Bipedalism in evolutionary context
• Bipedalism first trait to evolve in hominid lineage
• Ecological selective pressures at work (major
changes in climate)
Bipedalism in evolutionary context
• Individuals who used bipedalism were more
reproductively successful (able to secure food,
mates) & pass on genes associated with that
behavior
Why bipedalism?
ADVANTAGES:
Frees hands/arms for carrying things
Better visibility
Look larger (more threatening)
Keeps body cooler
Energy efficient for long distance travel or
activities
DISADVANTAGES:
More visible to predators
Loss of speed in running/turning quickly
Loss of or injury to one limb hinders mobility