Transcript 15-1 The Puzzle of Life`s Diversity

Unit 10 (Chapters 14-15)
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Scientists have observed that species do
change over time.
Over time, scientists believe that
characteristics change so much that new
species form.
Evolution is the slow, gradual change in a
population of organisms over time.
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English naturalist who
sailed on the HMS Beagle
in 1831-1836.
Made observations that
led to his “theory of
evolution”.
Collected thousands of
plant/animal specimens.
The most famous site he
visited were the
Galapagos Islands.
Wrote On the Origin of
the Species
Darwin returned 5 years later in 1836
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Most well known stop on Darwin’s voyage.
Small group of volcanic islands 1000 km West of
South America
Different climates on each island.
Island species vary from mainland species & from
island-to-island species
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Darwin noticed that the
animals/plants on the
Galapagos Islands were very
similar to those in nearby
Ecuador.
Specifically, the finches on each
of the islands were different
than the finches in Ecuador.
Each finch had a different
shape beak depending on
the type of food it ate.
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Occurs whenever a physical barrier divides a
population which results in individuals no
longer being able to mate.
Can lead to the formation of a new species.
(speciation)
◦ This could explain the Galapagos finches.
◦ A natural disaster could have drove the finches
from Ecuador and forced them over time to evolve
into the unique species of finches we find on each
of the islands today.
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Darwin knew that organisms could be bred in
order to produce desirable traits in the
offspring.
This is called artificial selection.
Also called “selective breeding”
For example: if a dog breeder wants a litter of
chocolate labs, his best bet will be to breed
two chocolate labs.
Darwin began to think that this could occur
naturally in the environment.
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Darwin proposed in his book that evolution
happens through a process called natural
selection.
Natural selection states that organisms that are
best adapted to their environment will survive
and reproduce more successfully than other
organisms without the adaptations. AS A
RESULT, they will pass their adaptations on to
their offspring.
DRIVING FORCE BEHIND THEORY OF EVOLUTION!
1. The Struggle for Existence
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Competition for food, mates, living space,
water, etc.
Some organisms will die due to this.
2. Survival of the Fittest
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The strongest will be able to survive and
reproduce and pass on their traits to their
offspring.
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Fitness
◦ Ability of an Individual To Survive &
Reproduce
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Adaptation
◦ Inherited Characteristic That
Increases an Organisms Chance for
Survival
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 Adaptations
◦ Physical
Can Be:
 Speed, claws, quills, thorns,
mimicry, camouflage
◦ Behavioral
 Herds, packs, migration,
hibernation, etc.
 Fitness
is central to the process of
evolution.
 Individuals With Low “Fitness”:
◦ Die quicker
◦ Produce fewer offspring
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Key concept:
◦ Over time, natural selection
results in changes in the
inherited characteristics of a
population. These changes
increase a species’ fitness in its
environment
 Cannot
Be Seen Directly
 It Can Only Be Observed As
Changes In A Population Over
Many Successive Generations
◦ Radiation
◦ Fossil Record
 Key
Concept: Species today look
different from their ancestors
 Each Living Species Has
◦ Descended
◦ With Changes
◦ From Other Species
◦ Over Time
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Implies
◦ All living organisms are related
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A Common Descent
◦ All species, living & extinct, were
derived from common ancestors
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“Evidence” in favor of evolution can be found
in the sediment (layers of rock and soil that
has hardened over time).
Older layers are found beneath newer layers.
We find fossils in this sediment.
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A footprint left in clay
A fly trapped in amber
Dinosaur bones
Wooly mammoth
Using fossils, scientists have made a
“timeline” of life called the fossil record.
Evidence for Evolution – The Fossil Record
• Structural features with a common evolutionary
origin.
• Have the same function and/or arrangement.
• Used as evidence that these organisms may have
evolved from a common ancestor.
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Body parts of
organisms that
have no common
evolutionary
origin
(arrangement) but
have similar
functions.
◦ Do not have a
similar appearance
but have similar
jobs.
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A body structure in a present-day organism that
no longer serves its original purpose.
A structure becomes vestigial when the species
no longers needs it for its orignal function.
Examples: Whales have hip bones, but can’t walk. Blind
mole rats have eyes, but don’t use them for vision.
Blind mole rats
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Human appendix is thought to be a vestigial
structure.
It serves no purpose in humans.
Darwin believed it is basically the remnants of
a portion of the large intestine that our
supposed primate ancestors used to digest
leaves.
Evidence for Evolution - Comparative Embryology
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Many organisms have similar appearances in the
womb.
This leads biologists to believe they evolved from a
common ancestor.
Similarities in DNA Sequence
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Many organisms share similar DNA sequences.
The order of their base pairs is often similar, in
other words.