Transcript Darwin and His Theory of Evolution by Natural Selection

Darwin and His Theory of
Evolution by Natural Selection
Evolution- changes in the
characteristics of groups of
organisms over time
Charles Darwin was the first to
propose a feasible
mechanism for evolution. It
is called natural selection.
Evolution by Natural Selection is a theory.
What is a scientific theory?
Scientific Theory- an idea that is strongly
supported by evidence. It is generally accepted
and used to explain many observations.
*Remember: The word “theory” in everyday
language and in scientific language mean very
different things.
In everyday language, people use the word
theory to mean a hypothesis or an educated
guess.
Natural Selectiondifferential success in
survival and
reproduction of
individuals with
different phenotypes
(physical
characteristics)
resulting from
interactions with their
environments
Conditions Needed for Natural Selection: VISTA
1. Variation
There are a variety of forms of traits or
phenotypes.
Conditions Needed for Natural Selection: VISTA
2. Inheritance
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Only traits that are determined by an organism’s
genes will be passed to the next generation.
Some variation is caused by the environment, such as
the loss of a limb or the building of muscle. These
traits are not heritable, so they can’t be selected for in
the next generation.
What causes genetic variation?
1) Mutations- changes in the
DNA sequence can result in
new traits
2) Sexual Reproduction- New
combinations of traits can be
created in gametes during
meiosis.
The wide variety of gametes
created will join together to
make diverse offspring.
Remember natural selection can only act on the
heritable variation that EXISTS in a population.
Conditions Needed for Natural Selection:
VISTA
4. Survival and Reproduction
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Individuals compete for limited resources, such as food,
shelter, and mates.
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Individuals with traits best adapted for the environment
are able to out compete other individuals for resources,
allowing them to survive and reproduce more.
“Survival of the Fittest”
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Evolutionary fitness isn’t a measure of physical
fitness but of reproductive fitness.
Fitness- Relative ability to survive and produce
offspring in an environment
Conditions Needed for Natural
Selection: VISTA
4) Time
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Evolution occurs over generations.
Conditions Needed for Natural Selection: VISTA
5) Adaptations- an inherited characteristic that
increases an organism’s chance of surviving and
reproducing
Over time, natural selections causes adaptations to
become more common in a population.
Drug Resistant Bacteria Practice
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Variation existed in a population of bacteria. Some were
resistant to antibiotics, while some weren't.
The resistance was an inherited trait caused by a gene.
When treated with antibiotic, the resistant bacteria survived
and reproduced more than the nonresistant ones, which were
killed by the antibiotic.
Over time, the adaptation of drug resistance became more
common in each generation of bacteria.
Natural selection can lead to a variety of changes within a
population. These changes can be roughly grouped into three
categories:
1. Stabilizing Selection:
natural selection that
favors an intermediate
phenotype
Example: Birth weight,
Human height
Natural selection can lead to a variety of changes within a
population. These changes can be roughly grouped into three
categories:
2. Directional Selection: natural selection that favors an extreme
phenotype and causes a shift in the distribution curve
Example: Birth weight, Human height
Natural selection can lead to a variety of changes within a
population. These changes can be roughly grouped into three
categories:
3. Disruptive Selection: natural selection that favors two or more
extreme phenotypes are favored over any intermediate phenotype
Since Darwin’s time, several other forces of selection have been
explained:
1. Sexual Selection: adaptive changes in males and females
that lead to an increased ability to secure a mate.
Since Darwin’s time, several other forces of selection have been
explained:
2. Artificial Selection: adaptive changes in organisms that occur
because of human forces.