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Evolution
Evolutionary Process
Human Evolution
Evolution
• Evolution = progressive change in
characteristics of organisms as a
result of changes in genetic
composition
• Two important aspects
– Descent from a common ancestor
– Adaptation to the environment
• Adaptation = characteristic that makes it
more likely that an organism will survive
and reproduce in its environment
Evidence for Common Descent
From the Fossil Record
Living Organisms resemble extinct fossil forms.
Evidence for Common Descent
From the Fossil Record
Progressive changes from simpler to more complex
organisms can be seen in the fossil record.
Biogeographical Evidence
for Common Descent
Plants and animals of each continent are distinctive.
Biogeographical
Evidence for
Common Descent
Different island species resemble each other.
Biogeographical Evidence for
Common Descent
Island Populations resemble
those on nearby land.
The Galapagos finches resembled the
grassquit found on the coast of Ecuador.
Anatomical Evidence for Common
Descent: Homologous Structures
Flying
Swimming Running Grasping
Anatomical Evidence:
Vestigial Structures
Remnants of
hindlimb seen in
boa and whale
Functional hindlimb
in salamander
Evidence for Common Descent
from Biochemistry
Evidence for Evolution from Biochemistry
Similarities in sequence measured by
ease of separating DNA strands by heat
A Flowchart of Evolutionary Reasoning
Potential for
rapid reproduction
Formation of new
genotypes leads to
phenotypic variation
Relatively constant
resources and
population over time
Competition for
survival and
reproduction (1)
Variability in
structures and
behaviors
NATURAL SELECTION
On average, the fittest
organisms leave
the most offspring (2)
Some variability is
inherited; adaptations
increase in future
generations
(observations)
(conclusions)
EVOLUTION:
The genetic makeup of the
population changes over time,
driven by natural selection (3)
Adaptation
Darwin’s proposal
Originally, giraffe neck
length varied.
Competition for
resources causes
long-necked giraffes
to have the
most offspring.
Due to natural selection,
most giraffes now
have long necks.
Natural Selection
as the Mechanism
for Evolution
Applying Your Knowledge
1. Adaptation
2. Evolution
3. Natural selection
A. The mechanism for evolution is
B. A progressive change in the
characteristics of organisms is
C. A trait that makes a species
survival more likely is called a(n)
Hominid
bipedal
posture
Chimpanzee
Angiosperms
evolve 199.6 MYA
and forests spread.
Gorilla
4
3
Orangutan
Gibbon
2
Primate
ancestor
enters trees.
~45 MYA: There was
a common ancestor
for monkeys, apes
and hominids
New World Monkey
Tarsier
1
Lemur
70
Common ancestor
may have resembled a
tree shrew
Old World Monkey
Prosimians
~15 MYA: There was
a common ancestor
for all apes and
hominids
Anthropoids
Primate
Evolutionary
Tree
Hominoids
~7 MYA: There was
a common ancestor
for African apes and
hominids
60 50 40 30 20 10
Millions of Years Ago (MYA)
PRESENT
Adaptations of Primates
•
•
•
•
•
Opposable thumb
Well-developed brain
Nails instead of claws
Single birth
Extended period of
parental care
• Emphasis on learned
behavior
Australopithecus afarensis
An early hominid
Hominid Evolution
0
Millions of Years Ago (MYA)
1.0
Australopithecines
low forehead
projecting face
400 cm3 brain
Australopithecus
boisei
In Africa
Australopithecus
robustus
Homo
ergaster
Homo
Homo
neandertalenis sapiens
Australopithecus
africanus
2.0
Homo erectus
3.0
Australopithecus
afarensis
Homo habilis
In Asia
4.0
5.0
5.5
Ardipithecus
ramidus
Ardipithecus
ramidus kadabba
Genus Homo
distinct forehead
flat face
700–1,300 cm3 brain
Possible ancestor of
both A. africanus and
Genus Homo
Possible ancestor of
modern humans
Human Evolution
• Genus Australopithecus
– walked upright
– product of mosaic evolution = different body
parts change at different rates
• Smaller brain resembles apes
• Bipedal locomotion resembles humans
– ancestors of genus Homo
(not certain which species led to Homo
habilis)
Human Evolution
• Genus Homo
Homo ergaster
– Homo habilis = “handy man”
• produced tools
• teeth supported omnivorous diet
• enlarged speech area in brain
– Homo ergaster (in Africa)
• advanced tools, use of fire
• larger brain, taller body
• striding gait
neck of femur
femur
– early Homo sapiens
(based on Cro-Magnon fossils)
• compound tools
• larger brain
• language and culture,
including art
femur neck is
longer than
in modern
humans
Two Hypotheses for the
Origin of Modern Humans
0.1
ASIA
AFRICA
EUROPE
ASIA
AFRICA
Homo sapiens Homo sapiens Homo sapiens
Homo sapiens Homo sapiens Homo sapiens
interbreeding
1
interbreeding
migration of
migration of
Homo ergaster
Homo ergaster
Homo ergaster
Multiregional continuity
Millions of Years Ago (MYA)
Millions of Years Ago (MYA)
Homo ergaster evolves into modern
humans in Asia, Africa, and Europe.
2
EUROPE
0.1
Homo sapiens
1
2
Modern humans evolve
in Africa and migrate
to Asia and Europe.
migration of
Homo ergaster
migration of
Homo ergaster
Homo ergaster
Out of Africa
DNA Analyses Related to
Human Origins
Visit http://www.geneticorigins.org
and choose
Mitochondrial Control Region
Media and Animations
Solving the Mystery of the Neanderthals
Other Applications of DNA Analysis can be
found at http://www.dnai.org
Choose Applications, then Human Origins
Homo floresiensis
Homo erectus
Homo sapiens
A Newly-Discovered
(but extinct)
Species of Genus Homo
Applying Your Knowledge
1. Homo habilis
2. Australopithecus afarensis
3. Homo ergaster
A. Which species is the closest ancestor
to Homo sapiens?
B. Which species was the first to use
tools?
C. Which species is the earliest hominid?