Transcript 7A Evidence of Common Ancestry

7A Evidence of Common
Ancestry
Summary of Darwin’s Theory
Individuals with the VARIATIONS/ ADAPTATION
best-suited to their environment will survive
and reproduce.
Those not suited will be less likely to breed
(Survival of the fittest!)
Summary of Darwin’s Theory
Species change over time, by passing on their useful (and
harmful?) traits to their offspring
Summary of Darwin’s Theory
THEREFORE,
All species alive today
have therefore
descended with
modifications from
ancient ancestors
Summary of Darwin’s Theory
Ultimately, ALL organisms on Earth are
united into a single tree of life…
Darwin’s original sketchbook drawing
This is….
Common Ancestry – the concept that a
group of closely related species are all
descended with some modifications
from the same ancestor
Descent with modification –idea that
living species have descended with
changes due to adaptations and natural
selection from species that lived before
them
 Fossils – preserved
remains or traces of
ancient organisms
 evidence that the
world was much
older than once
thought
 Fossils show how
organisms have
changed over time
99% of species that once
lived are now extinct!!!
The Geological Timescale
Based on fossil evidence, it
appears that the nature and
diversity of life on our planet
has changed dramatically
throughout Earth’s history
Fossil Record
When comparing fossils found in rock layers, the
deeper the layer, the older the fossil.
Index Fossil – fossils of
species that are easily
recognizable, that
lived during a specific
geological time period,
with a wide geographic
range
Are used to determine
age of other fossils by
comparing.
Evidence of Evolution #2: Biogeography
Beaver
Biogeography
► The study of where species live now
and where species and their
ancestors lived in the past.
Beaver
Muskrat
Muskrat
► Shows common ancestry two ways:
1. Provide evidence as to how closely
related species change in different
environments/selection pressures
2. How distantly related groups have
evolved similar traits under similar
selection pressures
Capybara
Beaver and
Muskrat
Coypu
Capybara
Coypu and
Capybara
Coypu
Evidence of Common Ancestry #3:
Homology
• Homology is the study of similar
characteristics between organisms
• There are three major branches of
homology:
1. Anatomical Homology
2. Embryological Homology
3. Molecular Homology
Anatomical Homology
Homologous Structures
- Same structure, different
function
- Same ancestor, different
function
On first appearance, would
you say that a human hand,
a bat’s wing and a whale’s
flipper were the same
structure?
Beneath The Surface…
Homologous Structures –Same
structure different function
Evidence of Evolution
Analogous Structures: structures similar in
function, but not inherited from a common
ancestor.
• Same function, different structure
• different ancestor
Flight
Protection
Analogous structures have the same function
but evolved from different places.
-Analogous structures are also evidence for
evolution because they show that two
organisms that came from different ancestors,
when placed under the same environmental
pressures can evolve the same adaptations.
Vestigial Structures
Vestigial Structures
Structures that are inherited, but reduced in size
and not used anymore
Whale pelvic bone
Human tailbone
Human appendix
Embryological Homology
• Embryology - the study of developing animals in its earliest
stages
• Embryos give evidence for evolution because many different
kinds of organisms have embryos that look alike, suggesting
that they all evolved from a common ancestor.
The diagram below shows embryos of five different species:
pig, chicken, fish, turtle, and human.
Can you tell which is which?
Figured it out yet?
How about now?
Did you guess correctly?
Chicken – 2 ½ days
Human – 31 days
Pig – 21 days
Human – 9 weeks
Pig – 30 days
Lemur – 3 ½ weeks
Human face – 5 weeks
Pig – 30 days
Human – 6 weeks
Macaque monkey – 4 weeks
Limb Buds
Pig foot –
30 days
Human hand – 6
weeks
Chicken foot – 5
days
Human – 16 weeks
Chimpanzee – 18 weeks
Macaque monkey – 10 weeks
Human Embryo Development
Time Lapse Animation:
Click here for a time lapse animation.
4 weeks
Molecular Homology
• All living things contain DNA and RNA.
• Changes in Proteins, DNA and RNA can
be traced from ancestors to their
descendents.
• The fewer differences there are between
these molecules in different organisms,
the more closely related they are
Apple Protein
Celery
Protein
DNA of Chimpanzee,
Human, & Chicken
Note – there are more
differences between
the human and
chicken than the
human and chimp
With which organism
do we share a more
recent common
ancestor?
Chromosome 1
of different species
Chromosome
Homology
Chromosome comparison of
human, chimpanzee, gorilla,
and orangutan
Human &
Chimpanzee
Chromosomes
• Human on the left
• Chimp on the right
• Notice that Human
Chromosome #2
appears to be a
combination of
Chimp Chromosomes
#2 & 3
Checkpoint
The table below demonstrates the amount
of DNA overlap that five animals have with
the DNA of a chimpanzee.
Animal
DNA % Overlap with
Chimpanzee
Dog
54%
Cat
47%
Gorilla
87%
Human
97%
Giraffe
68%
Order the Animals From More Closely
Related to Least Closely Related in their
ancestral relationship with chimpanzees.