Human Evolution
Primate Classification
Characteristics:
– Eyes in front of the face
– Opposable thumb
– Well developed brain
– Omnivorous
D: Eukarya
K: Animalia
P: Chordata
C: Mammalia
O: Primate
Humans
Chimpanzees
The Geological
Time Scale
• Fossil Patterns were used to
create 5 Major Categories of
Time (Eras):
1. Archaean
2. Proterozoic
3. Paleozoic
4. Mezozoic
5. Cenozoic
Types of Evolution
Anagenesis
• New species from
heritable changes
through time (linear)
Cladogenesis
• New species from
speciation events
(branching)
Which pattern did human evolution follow?
Anagenesis?
Cladogenesis?
Aside: Hypothesis Driven Science
• How do you test hypotheses on the past?
– Experimentation is not possible
• Need to come up with hypotheses that can be
tested by observations
Evolution
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Fossils
Biogeography
Comparative Morphology
Comparative
Development
• Comparative Biochemistry
FOSSILS
1. The preserved remains or
traces of organisms from
the past
2. Found in sedimentary rock
layers created by water
deposition
3. Dated and used to
determine Earth’s
biological past
• Over time, fossils found in
stratified soil layers show
consistent patterns in the diversity
of living organisms
Outstanding and mysterious question: what has happened to our species
since the divergence from the lineage leading to chimpanzees?
On November 30, 1974 Donald Johanson and Tom Gray discovered a remarkably
complete hominid fossil in Hadar, Ethiopia. This fossil became known as ‘Lucy’ and
was later determined (by radiometric dating) to be 3.2 million years old. This is
one of the most compelling missing link fossils ever found.
Lucy was not human—clearly a different species,
which was named Australopithecus afarensis—but she
was clearly hominid and very different from chimps.
What Makes A Hominid? - Bipedalism
• Primary feature distinguishing
hominids from other hominoids is
walking erect on two legs – erect
bipedalism
Why did bipedalism become the
primary adaptation of hominids?
1.
Carrying behavior
2. Heat stress - facilitates heat loss through
convection by exposing body to air currents, only
humans have sweat glands that produce moisture
to cool body
3. Most energy efficient way to travel long distances
4. Allows for better vision in open environments &
defensive action against predators by freeing
hands to throw objects
Was Lucy bipedal?
The impressions
in the ash suggest
that weight was
shifted during walking
like a modern bipedal
human rather than
like a modern
chimpanzee.
Footprints in volcanic ash
at Laetoli (3.7 million years
old)
Chimp
Human
Other evidence for bipedalism.
Chimp pelvis
Angle that the femur
makes with knee
also is important, and
different in bipeds than
in chimps.
Lucy pelvis
This arrangement more
efficient for bipedalism.
Variation within and between species
Homo sapiens
Australopithecus afarensis
How much “normal” variation can there be within a species?
Normal % Variation
Standard Curve (Bell-shaped)
Mean
1 sd=66%
2 sd=95%
N%V=((4*sd)/mean)*100
Lab Hints
• “R” program for statistics is on CU Learn website
• After completing one set of skull measurements, I will
give you a handout with the rest
• Measure facial projection with zygomatic arches
parallel to the floor (skull tilt affects the measurement)
• Lab report due next week
• There will also be a quiz next week.