Download Natural Selection

Nature of Science
Theory:
• An explanation for many related
observations based on extensive
scientific and experimental
evidence in many conditions.
Science
Religion
Microevolution vs.
Macroevolution
Objective 1: Distinguish between the
process of evolution (microevolution)
and theory of evolution
(macroevolution).
Evolution: (Microevolution)
• Definition: the change in gene frequency
of a population over time.
Evolutionary Theory: (Macroevolution)
• The theory that life originated from one
common unicellular ancestor and became
diverse through natural selection and
speciation.
Necessary Vocabulary
Variation:
differences between individual members of a
population. (Physical, behavioral, biochemical,etc)
Remember: Variation occurs from...
• Genetic Mutations
• Crossing Over
• Independent Assortment
• Fertilization
Necessary Vocabulary
Adaptation:
inherited trait that increases an
organism's chances of survival and
reproduction in a particular
environment.
Necessary Vocabulary
Species:
• An interbreeding, or
potentially interbreeding,
population that produces
healthy, fertile offspring.
Necessary Vocabulary
Population:
A group of organisms of the same
species living in a specific area.
Story Time
The ancestors of giraffes had short
necks. In order to eat leaves high
up in the trees, individuals had to
stretch their necks. As a direct
result of this activity, the offspring
of these individuals had longer
necks. They, too, stretched their
necks to reach even higher leaves,
and transmitted their even longer
necks to their offspring. Over time,
as a result of the striving of
individual giraffes, modern-day
giraffes have very long necks.
Story Time
The ancestor of modern giraffes would have
been a mammal with a short neck. In the
ancestral population, a mutation arose that
lengthened the neck of any animal that
happened to harbor the mutation. These
individuals were able to reach leaves higher in
the trees than were other individuals. As a
result, they were able to eat more and produced
more offspring. Gradually, the long-neck
mutation spread through the population.
Sometime later, another mutation arose, which
lengthened necks even more, and it spread
through the population in a similar manner.
Eventually, a number of mutations, each of
which helped lengthen necks, spread
throughout the population, resulting in the long
necks we see today.
Objective 2: Describe and Identify the conditions
necessary for natural selection to occur.
***Natural Selection***
• In 1859, after 15 years of observations and
research, Charles Robert Darwin published On
the Origin of Species. In this book, he
introduced his "Theory of Evolution" based on
Natural Selection.
***Natural Selection***
This theory states that the following conditions must
exist for evolution to occur...
1. There must be VARIATION in a population.
2. There is a change in the environment. (The video
calls this… Struggle for existence)
3. Those organisms with favorable variation survive.
4. Individuals who survive, reproduce, and pass on the
favorable variation to their offspring.
***Adaptations occur because of Natural Selection***
Natural Selection vs. Artificial
Selection
Obj. 4: Compare & contrast natural
and artificial selection.
Natural Selection vs. Artificial Selection
• Natural Selection: conditions in nature
determine what survives and reproduces.
• Resulting adaptations allow better survival in
the organisms' natural environment.
• Example:
– Peppered Moth
– Darwin’s Finches
– White Lizards of New Mexico
Natural Selection vs. Artificial Selection
• Artificial Selection: humans decide what
survives and reproduces.
• Resulting adaptations serve the needs of
humans.
• Examples:
– Farmers breed cows to produce more milk.
– Humans breed horses for quickness and strength.
– Genetically Modified Foods
Speciation
Obj. 6: Describe a scenario where natural selection
leads to speciation.
Speciation
What is speciation?
• The evolution of one or
more species from an
original ancestor species.
Speciation
What are the three-steps in order for speciation
to occur?
Step 1: Isolation of population
Step 2: Adaptation/Evolution
Step 3:. Reproductive Isolation
Evidence for
Evolution
Obj. 7: Identify & explain evidence of evolution
including trends in history of life on earth.
Evidence for Evolution
• Degree of relatedness between two species
depends on how long ago they shared
common ancestors. To determine
relatedness, scientists can use:
– Comparative Anatomy
– Comparative Embryology
– Comparative DNA
– Fossil Records
Comparative Anatomy
• Homologous Structures:
– Body parts that have the same general
structure but different functions.
– Due to common ancestors adapting to
different environments
– Examples: (change in notes)
• Human arm, whale fin and bat wing
Comparative Anatomy
• Analogous Structures:
– Body parts that have the same function but
do not have a similar structure
– Due to similar environments and lifestyles
– Not common ancestors
– Examples: Insect wings and Bird wings
Comparative Anatomy
• Vestigial Structures
– Genetic “Leftovers”
– Often smaller in size
– Often disused
– No longer hold any valuable adaptation for
survival
– Suggest structures of common ancestry
– Examples: tail bones, human appendix, body hair,
goose bumps, wisdom teeth, hip bones in snakes,
etc.
Comparative Embryology
• Embryology
–Study of early stages of organism
development.
–Embryos of related organisms
develop similarly.
Comparative DNA
• DNA Comparisons
– Comparing DNA to determine relationships
– The more similar DNA sequences are in
organisms, the more related those organisms
are.
– Examples:
• Hemoglobin – carries oxygen
• Cytochrome C – enzyme involved in cellular
respiration
Fossil Records
• Fossils are the remains of a living thing
that have been preserved in rock
• Show changes in organisms over time
– Ancestors
– Transitional species
• By dating the rock, scientists can tell when
the organism was alive.
• Also gives clues to how surroundings have
changed over time
• Difficulty: fossil record is incomplete
Fossil Records Cont…
• Rock Layers
– Age of fossils can also be determined by the
rock layer in which they are found.
– Older rocks are found on the bottom
– Younger rocks are found closer to the top
• Mass Extinction
– When lots of fossils suddenly disappear
– Usually evidence of environmental change
• KT extinction (dinosaurs)