Transcript Anatomical Evidence for Common Descent

Evolution
Evolutionary Process
Human Evolution
Evolution
• Evolution = 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.
Cactuseater
Insect-eater
Seed-eater
Natural Selection led to beak sizes
and shapes suitable for different food sources
Biogeographical Evidence for Common Descent
Island Populations resemble
those on nearby land.
The Galapagos finches resembled the
grassquit found on the coast of Ecuador.
Recent studies suggest that the finch ancestor
may have originated from the Caribbean islands.
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
Anatomical Evidence: Vestigial Structures
In fish, these pouches
form the gill slits. In
humans, one of the
pouches does not persist
past this embryonic stage.
Other pouches give rise to
structures of the ear,
tonsils, parathyroid and
thymus.
The tail has 12 vertebrae
at this stage. Numbers 612 are lost through cell
death and numbers 4-5
are reduced. The coccyx
is the remainder of
vertebrae 1-5.
Evidence for Common Descent
from Developmental Biology
Evidence for Common Descent from Biochemistry
A Flowchart of Evolutionary Reasoning
Formation of new
genotypes leads to
phenotypic variation
observations
inferences
Variations exist
between members
of a population
Relatively constant
resources and
population over time
At least some
variation is hereditary
More offspring are
born than survive and
reproduce
Individuals whose
inherited traits give a
higher probability of
survival and reproduction
leave a greater number of
offspring
Favorable traits will
accumulate in the population
over generations
Adaptations
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
~7 MYA: There was
a common ancestor
for African apes and
hominids
bipedal posture
Primate
Evolutionary
Tree
~15 MYA: There was
a common ancestor
for all apes and
hominids
~45 MYA: There was
a common ancestor
for monkeys, apes
and hominids
Common ancestor
may have resembled a
tree shrew
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
Hominin Evolution
In Africa
In Asia
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
Multiregional continuity
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