Download Biology 03/04/13 15.3 cont`d Common Descent All species (living or

Biology
03/04/13
15.3 cont’d
Common Descent
All species (living or
extinct) that were
derived from common
ancestors
A single “tree of life”
links all living things
III. Evidence of Evolution
Living things have been
evolving on Earth for
millions of years.
Evidence for this
process could be found
1. Fossil Record
2. Geographic
Distribution of
Living Species
3. Homologous
Structures of Living
Organisms
4. Similarities in
Embryology (Early
Development
Fossil Record
Fossils are remains of
ancient life
a. Species life
b. Die to be found in
the Earth’s layers of
rock
c. Older layers of rock
determine when
the species lived
Geographic Distribution of Living Species
Animals on continents
living under similar
ecological conditions
1. Exposed to similar
pressures of natural
selection
2. Different animals
ended up evolving
with certain striking
features in common
Homologous Structures of Living Organisms
Provide evidence that
all four-limbed
vertebrates have
descended with
modification from
common ancestors
1. Front Limbs
Bird Wings
Bird
Skeletons
Bones
support
wings of
bats
Vestigial Organs
Bat Wings
Crocodiles
Dinosaurs
Humans
Whales
Mammals
Organs of many
animals that are so
reduced in size that
they are just vestiges or
traces homologous
organs in other species
1. May not affect the
organisms ability to
survive or
reproduce
2. Natural selection
would not cause the
elimination of that
organ
Ex. Legs, tails
Similarities in Embryology (Early Development)
The early stages of
many animals with
backbones are very
similar. This does not
mean that a human
embryo is ever
identical to a fish or a
bird embryo.
IV. Summary of Darwin’s Theory
1. Individual organisms differ and some of this
variation is heritable
2. Organisms produce more offspring than can
survive and many that do survive do not
reproduce
3. Because more organisms are produced than
can survive, they compete for limited
resources (food, shelter)
4. Each unique organism has different
advantages and disadvantages in the
struggle for existence. Individuals best
suited to their environment survive and
reproduce most successfully. These
organisms pass their heritable traits to their
offspring. Other individuals die or leave
fewer offspring. The process of natural
selection causes species to change over
time.
5. Species alive today are descended with
modification from ancestral species that
lived in the distant past. This process by
which diverse species evolved from
common ancestors unites all organisms on
Earth into a single “tree of life.”