Transcript Bio 226: Cell and Molecular Biology

Evidence for macroevolution
Strongest = Fossil Record
• order of fossils in sediments
• oldest at bottom
• date with radioisotopes
Fossil Record
Find successive change in groups of organisms:
"missing links"
• whale legs & shape
Fossil Record
Find successive change in groups of organisms:
"missing links"
• whales
• horse size
Fossil Record
Find successive changes: "missing links"
• whale legs & shape
• horse size
• hominid cranium
Evidence for macroevolution
DNA: many genes are so similar that they must
have diverged from a common ancestor:
Align genes, count diffs
Evidence for macroevolution
DNA: many genes are so similar that they must
have diverged from a common ancestor
Align genes, count diffs
# changes says when 2 spp. split
Molecular clocks
Align genes, count diffs
# changes tells when 2 spp. split
Calibrate with fossil record
Mitochondrial DNA traces Mom
• only comes from mom & doesn’t recombine
• says we split ~ 170,000 years ago
Y chromosome
traces Dad
• only comes from
dad & doesn’t
recombine
•Says we entered
Europe ~ 50,000
years ago
Evidence for macroevolution
Fossil record
DNA
Comparative anatomy: same bones derived from
common ancestor:
shape & function
has changed
Evidence for macroevolution
Fossil record
DNA
Comparative anatomy: same bones derived from
common ancestor: shape & function changed
Vestigial structures: non-functional left-overs
Evidence for macroevolution
Fossils
DNA
Comparative anatomy
Embryos retrace evolution as they develop
Embryos retrace phylogeny
Embryos retrace evolution as they develop
Embryos retrace phylogeny
Embryos retrace
evolution as they
develop
Close spp look
alike longer
Convergent evolution
similar selection results in organisms that look alike
e.g. desert plants: American cacti & African
euphorbs look alike but unrelated
Convergent evolution
similar selection -> organisms look alike
e.g. Australian
marsupials resemble
American placental
mammals
Convergent evolution
similar selection -> organisms look alike
e.g. Australian
marsupials resemble
American placental
Mammals
Fill same niche:
role in nature
Analogy vs homology
Analogous: look alike but different origin
Bird vs insect wings
Analogy vs homology
Analogous: look alike but different origin
Bird vs insect wings
fins vs flippers
Analogy vs homology
Analogous: look alike but diff origin
• Bird vs insect wings
• fins vs flippers
Homologous: look different, same origin
Pace of evolution
Some plants evolve rapidly
Mammals evolve slowly
Starfish evolve very slowly
Pace of evolution
Gradualism: gradual evolution
Large populations
Slow change in selection
Pace of evolution
Gradualism: gradual evolution
Large populations
Slow change in selection
Punctuated equilibria: evolve in spurts
Pace of evolution
Punctuated equilibria: evolve in spurts
small populations
Genetic drift
alters gene
pool
Rapidly adapt
then reach
equilibrium
Pace of evolution
Mass extinctions:
O2 poisoning 2 b.y.a. killed most bacteria
Mass extinctions
O2 poisoning 2 b.y.a. killed most bacteria
96% of species died at end of Permian
Asteroid 65 m.y.a. killed dinosaurs
Mass extinctions
O2 poisoning 2 b.y.a. killed most bacteria
96% of species died at end of Permian: asteroid?
Asteroid 65 m.y.a. killed dinosaurs
Man is causing another mass extinction!
Enable evolution of new spp!
Mass extinctions
Enable evolution of new spp!
Formerly occupied niches become available
major factor in success of mammals