Transcript ch 15 evolution

Chapter 15 “The Theory of
Evolution”
• The central thought behind evolution is
that organisms must survive and produce
healthy offspring in order to continue their
species.
• In 1859, Charles Darwin published
evidence that species do evolve.
• Almost all scientists accept that evolution
is the basis for the diversity of life on
Earth.
Four Principles of Natural Selection
1. Variation exists
within the genes of
every species as a
result of random
mutations.
2. In particular
environments,
some individuals
within a population
are better suited to
survive & have
more offspring
3. Favorable traits will
increase in a
population.
4. Evidence that living
species evolved
from organisms that
are extinct.
Lamarck’s Law of Use and Disuse
• Before Darwin’s proposal of evolution, a French scientist
Jean Baptiste Lamarck, proposed a mechanism for
evolution.
• He said that evolution occurs through the use and disuse
of physical features by individual members of a species.
• He believed that in the lifetime of an individual,
structures increase in size because of use or reduce in
size because of disuse.
• He then reasoned that the modified part is then passed
on to the organism’s offspring.
• If Lamarck was correct, the offspring of bodybuilders
would be born with enormously developed muscles.
Natural Selection
1.
•
•
“Struggle for Existence”:
individuals compete for
limited resources (water,
living space, light, food).
In this struggle, the
predators that are faster or
have a particular way of
catching other organisms
can catch more prey.
Those prey that are faster,
better camouflaged, or
better protected can avoid
being caught.
2. “Survival
•
•
•
of the Fittest”: Some inherited traits give
individuals an advantage in coping with
environmental challenges, allowing them to
survive longer & produce more offspring
Individuals differ in their traits.
They may differ in size, coloration, running
speed, resistance to disease, etc. this variation
must be inherited for it to influence natural
selection
Individuals with characteristics that are not suited
for their environment, either die or leave few
offspring
Individuals that are better suited to their
environment, survive and reproduce most
successfully. Because individuals with
advantageous traits have more offspring, each
new generation contains a greater proportion of
the offspring with these traits than did the
Descent with Modification
• Over long periods of time, natural
selection produces organisms that have
different structures, establish different
niches or occupy different habitats.
• As a result, species today look different
from their ancestors.
Adaptation
• Organisms differ from place to place
because their habitats present different
challenges
• Each species has evolved in response to
its particular environment
• The changing of a species that results in it
being better suited to its environment is
called adaptation
Isolation of Species
• Populations of the same species living in
different locations tend to evolve in different
directions
• As 2 isolated populations of the same species
become more different over time, they may be
unable to breed with another
• Generally, when individuals of 2 related
populations can no longer breed, the 2
populations are considered different species.
Isolation leads to species formation
• The Kaibab squirrel and the Abert squirrel
populations became isolated from each
other 10,000 years ago.
• The Kaibab squirrel lives on the North Rim
of the Grand Canyon
• The Abert squirrel lives on the South Rim
• Over time, the Kaibab squirrel evolved a
black belly & other characteristics
• The Abert squirrel evolved a white belly.
Kaibab squirrel
Abert squirrel
Evidence of Evolution
• Fossils offer the most
direct evidence that
evolution takes place
• Darwin’s theory is
accepted by scientists as
the best available
explanation for the
biological diversity on
Earth
Most scientists agree on the
following three points:
1. Earth is about 4.5
billion years old
2. Organisms have
lived on Earth for
most of its history
3. All organisms living
today evolved from
earlier, simpler lifeforms
Fossil Record
Reasons for an incomplete fossil
record:
1. Many species have lived in
environments where fossils do
not form.
2. Their bodies are eaten and/or
scattered by scavengers.
3. It is difficult to form a fossil
from a soft bodied animal as
opposed to a hard bodied
animal.
Anatomy & Development Support
for Evolution
• Bones and other structures that are
present in organisms but are reduced in
size and either have no use or have a less
important function are vestigial structures
• As different vertebrates evolved, particular
sets of bones evolved differently
• Similarities in bone structures suggest that
all vertebrates share a common ancestor
• Such structures are called homologous
structures
• The forelimbs of
all vertebrates
are made from
the same basic
groups of bones
• Homologous
structures are
structures that
share a common
ancestry
Embryonic Development
DNA Contains a Record of
Evolution
• The more similarities
found in two DNA
sequences, the more
closely related are the
organisms
Hemoglobin Comparison
Species
Gorilla
Amino Acid
differences
1
Rhesus
monkey
Mouse
8
Chicken
45
Frog
67
Lamprey
125
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