Transcript powerpoint note presentation

Evidence for Evolution
Evidence for Evolution
• Darwin argue that living things have been
evolving on Earth for millions of years.
Evidence for this process could be found:
– In the geographical distribution of living
species
– In the homologous structures of living
organisms
– In the similarities in early development
– In the fossil record
Evidence of Evolution
Evidence of
Evolution
includes
The fossil record
Geographic
distribution of
living species
Homologous
body structures
Similarities
in early
development
which is composed of
which indicates
which implies
which implies
Physical
remains of
organisms
Common
ancestral
species
Similar genes
Similar genes
Geographic Distribution of Living
Species
• Similar animals in different locations are the
product of different lines of evolutionary descent
• Because some animals on different continents
live under similar ecological conditions, they are
exposed to similar pressures of natural
selection. Because of this, different animals
evolve certain features in common even though
each descended from different ancestors.
Geographic Distribution of Living
Species
Beaver
Beaver
NORTH
AMERICA
Muskrat
Muskrat
Beaver and
Muskrat
Coypu
Capybara
Capybara
SOUTH
AMERICA
Coypu
Coypu and
Capybara
Homologous Structures of Living
Species
• Similarities among bones of different
vertebrates, such as reptiles, birds, and
mammals. Some limbs are arms, others are
wings, legs, or flippers
• Limbs differ greatly in form and function, yet are
made from the same bones
• Each of these limbs has adapted in ways that
enable organisms to survive in different
environments
• Structures that have different mature forms, but
develop from the same embryonic tissues are
homologous structures
Homologous Body Structures
Turtle
Alligator
Typical primitive fish
Bird
Mammals
Homologous Structures of Living
Species (continued)
• Not all homologous structures serve important
functions. These organs are reduced in size and
are traces of homologous organs of other
species = vestigial organs.
– They probably served a purpose a long time ago
– Ex. Whales have a pelvis (hip bone), but obviously
don’t have legs = at one point, they probably walked
– Ex. Humans have a tail bone, but obviously no tail =
at one point, they probably had a tail
– Ex. Humans have an appendix (part of the digestive
tract) that doesn’t do anything = at one point, it
probably did
Similarities in Early Development
• Early stages (embryos) of
many animals with
backbones are so similar
they can be hard to tell
apart
• Embryonic cells develop
in similar order =
homologous structures
Fossil Record and Evidence
• Fossil – remains of ancient life
• Different layers of rock form at different times in
Earth’s history
• Fossils that had formed in the different layers of
rock were evidence of gradual change over time
• Fossil record – provides evidence about the
history of life on Earth. It also shows how
different groups of organisms have changed
over time
• 99% of all species that ever lived on Earth have
become extinct
How Fossils Form
• Not all organisms that die become fossils
– 1) Organism dies and is buried in sediment
– 2) Soft tissues of the organism decay
– 3) Sediment becomes new rock
Water carries small rock
particles to lakes and seas.
Dead organisms are buried
by layers of sediment, which
forms new rock.
The preserved remains
may later be discovered
and studied.
Interpreting Fossil Evidence
• Paleontologists determine the age of
fossils using two techniques
– Relative dating
– Radioactive dating (aka absolute dating)
Relative Dating
• Average age of fossil is determined by
comparing its placement with that of
fossils in other layers of rock
• Rock layers form in order by age –
oldest layers on the bottom and more
recent layers on top. What does this
mean about the fossils found there?
• Index fossils used to compare the
relative ages of fossils. Index fossils
are organisms that are easily
recognized, existed for a short period,
and had a wide geographic range
• ****Relative dating provides NO
information about a fossil’s exact age in
years****
A trilobite – an index fossil
– it lived everywhere about
540 mya
Radioactive Dating (aka Absolute
Dating)
• ****Used to assign exact ages to rocks and fossils****
• Radioactive elements in rocks decay at a steady rate
measured in a unit called half-life
• Half-life – length of time required for half of the
radioactive atoms in a sample to decay
• In radioactive dating, scientists calculate the age of a
sample based on the amount of remaining radioactive
isotopes it contains
• Different radioactive elements have different half-lives
and therefore provide natural clocks that “tick” at
different, but constant rates
Comparing Relative and Absolute Dating of Fossils
Can determine
Is performed by
Drawbacks
Relative Dating
Absolute Dating
Age of fossil with respect to
another rock or fossil (that is,
older or younger)
Age of a fossil in years
Comparing depth of a fossil’s
source stratum to the position
of a reference fossil or rock
Determining the relative
amounts of a radioactive
isotope and nonradioactive
isotope in a specimen
Imprecision and limitations of
age data
Difficulty of radioassay
laboratory methods