Transcript evolution_-_evidence_ch._15_part

Evidence of Evolution
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Fossils
Vestigial Structures
Embryonic Development
DNA sequences
Fossils
• Preserved remains or imprint of ancient
organisms
• Form mostly when sand/silt settle from
water over dead organism 
sedimentary rock
• Fossil record is incomplete:
– Most living things leave no trace;
– Fossils vulnerable to weather &
erosion;
– Soft parts do not fossilize well.
• Provide much of what we know about
life’s history.
• Fossils are dated by a chemical method
called radioisotope dating.
Fossil Formation
We can only date igneous rock using radioactive isotopes;
Sedimentary rock is dated using layers of igneous rock above and
below it.
Radioactive Isotopes Are Used to Date Fossils
/ Geological Layers of the Earth
Geology - Law of Superposition
(add to notes)
 Newest layer
 Oldest layer
Sedimentary
layers are
deposited in a
time sequence,
with the oldest on
the bottom and
the youngest on
the top (provided
that there is no
overturning).
Plate Tectonics
affects
biogeography
(how species
are distributed
in geographical
areas)
What drives plate tectonics?
Analogy:
hard-boiled egg
Fossil Record & Human Evolution
Some fossils are famous!
“Lucy” (Australopithecus afarensis ) -discovered 1974, Ethiopia; ~3.4 m.y.a.; 40%
complete
Hip structure shows bipedal upright walk,
brain capacity comparable to that of ape 
Lucy replica
Reconstruction
Some fossils are famous!
“Ardi” (Ardipithecus ramidus )
~4.4 m.y.a. – Eastern Africa – fossils
found 1990’s - 2004
Evolved a few million years after
humanity’s evolutionary family
diverged from a lineage that led to
chimpanzees, but it is not clear exactly
how this species is related to other early
hominids.
Fossils of this ancient hominid display a
mixture of traits suitable for two-legged
walking and tree climbing
An artist’s interpretation shows how a
4.4-million-year-old female Ardipithecus
may have looked 
“Living Fossils”
Species that are relatively unchanged
from their distant ancestors:
Coelacanth
a living fossil fish
Horseshoe crab
a living fossil
arthropod
Embryonic Development
Ex:
Vertebrate
embryos
share a tail
and gill slits
at early
stages of
development,
revealing the
presence of
genes that are
no longer
expressed in
the adult.
Human Embryonic Development
Vestigial Structures
Inherited, No Longer Functional
Atavistic Traits are thought to be caused by the expression of
genes that had been silenced during evolution.
(Atavus = grandfather/ancestor  expression of an ancestral trait)
X-ray image of an
atavistic tail found in a
six-year old girl
(from Palomar.edu)
Homologous Structures
Similar Structure from Common Ancestry
Lizard
Human
Cow
Bird
Bat
Whale
Analogous Structures
Similar Function, NOT Common Ancestry