Transcript History of Evolutionary Biology

Topic 3:
Evidence for evolution
Fossil record
• The sequence that fossils appear within layers (strata) of sedimentary
rocks
• Three types of fossils:
– Mineralized bones and shells
– Trace fossils
– Preserved remains
• Aging of fossils
– C-14
– U-235
Fossil record
• Earliest fossils= stromatolites
• 3.5 billion years old
• Mineralized layered mats of
ancient cyanobacteria (we
can thank them for early
oxygen)
Proterozoic rocks (~2 billion years old)
Fossil Record
“Descent with modification”
Biogeography
Homologous
Structures
• Similar or different
function
• Similar structure
• Indicates common
ancestors
Homologies can be used to infer evolutionary history
Vestigial organs
• Remnants or whole structures that once
served a function in an ancestor but are
useless now
• Examples: human ear muscles, hind-leg and foot
bones in whales
Embryonic development
• Many organisms share
traits as embryos that are
not kept as adults.
• For example, at one stage
of development in the
womb, reptile, bird, and
mammal fetuses have
structures resembling gills
and they all have tails.
Biochemical experiments
• Stanley Miller (1953): Miller-Urey experiments
– Simulated the conditions of primeval earth (~4 billion years
ago)
– Ocean + atmosphere (water vapor, methane, ammonia) +
electrical charge (lightning)
amino acids and other organic compounds that are today
found in living things
– Proved that organic molecules can be synthesized from
inorganic molecules
– These experiments have been repeated independently many
times, with similar results
• Since then, many meteorites have been analyzed
and found to contain amino acids!
Biochemical evidence
• How did we get living organisms from
organic compounds?
– Remember the properties of cell
membranes (phospholipid bilayer)?
– Protobionts (lab experiments confirm)
– Self-replicating RNA (lab experiments)
Prokaryotes and endosymbiosis
• Chloroplasts and mitochondria are probably
remnants of those smaller prokaryotes
– Evidence: both have their own DNA, replicate themselves
like bacteria (binary fission)
Molecular evidence
• Universal code of life (DNA)
• Conserved sequences of DNA
– Example: gene for cytochrome c
• Protein synthesis
– RNA
– Ribosomes
– 20 amino acids
Primate family tree
If we scaled time to 24 hours…
Modern humans (Homo sapiens) appear
about 2 seconds before midnight
Age of
reptiles
Insects and
amphibians
invade the land
Plants
invade
the land
Age of
mammals
Recorded human history begins 1/4
second before midnight
Origin of life (3.6–3.8 billion years ago)
Fossils
become
abundant
Fossils
present
but rare
Evolution and
expansion of life