Transcript Evolution

Evolution of Life
How Organisms Survive
What Is Necessary To Survive?
• Variation is an appearance of an
inherited trait or behavior that
makes one organism different from
others in the same species.
• Adaptations are variations that make
an organism better able to survive.
Variations vs. Adaptations
How Does Evolution Work?
• Natural selection is the
process where the organisms
that are better adapted to
their environment are more
likely to survive and
reproduce.
Charles Darwin
Theory of Natural Selection
• Charles Darwin is credited as
discovering the mechanism, or tool,
for evolution to occur. He called this
the theory of natural selection.
• His theory can be summarized as
“survival of the fittest”.
Theory of Natural Selection
1. Organisms produce more offspring than
can survive. Ex. Tree seeds, salmon eggs.
2. Variations exist within populations.
3. Some variations are more advantageous
for survival. The struggle to survive
results in competition.
4. Over time only those individuals with
advantageous variations will survive and
reproduce.
Natural Selection
Species Are Always Changing
• Evolution is the change in the
hereditary features of a population
of organisms over time.
• When a species changes it is said to
have evolved.
How Do Species Change?
• A mutation is a permanent change in a
gene or chromosome that changes the
organism in some way.
– Ex. Size, shape, color, behavior, etc.
• Some mutations are harmful.
• Some mutations are beneficial.
Mutations
Mutation vs. Adaptation
• Only beneficial mutations are
adaptations because these provide an
advantage to survival.
Mutation vs. Adaptation
What Evidence Is There Of
Evolution?
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Evolution of species is evident in:
Fossils
Cell Structures
DNA
Homologous Structures
Embryos
Shared Characteristics
Fossil Evidence of Evolution
• Fossils are remains of life from earlier
times.
• Fossils are usually found in rock layers
that provide a time reference:
– Youngest (most recent) layers are on top.
– Oldest layers are on the bottom.
• Fossils provide evidence about the past
climates and/or landscapes.
Fossil Evidence
Cell Structure Evidence of Evolution
• Studying cell structures shows
similarities between organisms.
• A comparison of ancient and modern
cells shows similarities in cell
membranes and cytoplasms.
Cell Structure Evidence
DNA as Evidence of Evolution
• Studying DNA shows more
similarities between organisms.
• The more similar the DNA, the more
closely related the species are.
• Ex. The DNA of Gorillas and Humans
are ~92% similar whereas the DNA of
any two humans is 99.9% similar.
DNA Evidence
Homologous Structures as
Evidence of Evolution
• Homologous structures are body
parts of different organisms that
are similar in origin and structure.
• Ex: human arm, bird wing, bat wing,
and dolphin flipper all have similar
bone structure and function and show
the relatedness of the species.
Homologous Structures
Homologous
Structures
Embryo Evidence of Evolution
• Studying the similarity seen in the
embryos of vertebrates shows that
they share a common ancestor.
Embryo Evidence
Shared Characteristics as
Evidence of Evolution
• Primates are a group of mammals,
including monkeys, apes and humans,
that share many characteristics.
• For example, they share:
– Opposable thumbs
– Flexible shoulders
– Binocular vision
Opposable Thumbs