What is Evolution?
Simply:
Change Over Time
Biologic Evolution
the change in species over time
A.K.A. descent with modification
This definition encompasses:
small-scale evolution
changes in gene frequency in a population from one
generation to the next
large-scale evolution
the descent of different species from a common
ancestor over many generations).
Mechanisms of Evolution
The processes of evolution
Evolution is the process by which modern organisms have descended from ancient
ancestors. Evolution is responsible for both the remarkable similarities we see
across all life and the amazing diversity of that life — but exactly how does it
work?
Fundamental to the process is genetic variation upon which selective forces can act in
order for evolution to occur. We will focus on:
Descent and the genetic differences that are heritable and passed on to the
next generation;
Mutation, migration (gene flow), genetic drift, and natural selection as
mechanisms of change;
The importance of genetic variation;
The random nature of genetic drift and the effects of a reduction in genetic
variation;
How variation, differential reproduction, and heredity result in evolution by
natural selection; and
How different species can affect each other's evolution through coevolution.
What is natural selection?
•
The process in nature that results in the most fit (best adapted)
organisms producing offspring.
•
3 steps: variation --> selection --> reproduction
Survival of the Fittest Individuals with characteristics best suited to their environment
survive.
Individuals in a population who are best suited to the
environment will be selected for (survive) and pass their
genes (and traits) to their offspring.
What is the relationship
between variation and fitness?
➢ Variation •
Differences amongst individuals in a population (both in genes
and physical traits), that result from sexual reproduction.
➢ Fitness •
The combination of physical traits and behaviors that help an
organism survive and reproduce in its environment.
Populations of organisms have a variety of physical traits and
behaviors. Certain individuals have traits and behaviors that
are better suited to certain environments than others.
What is the relationship
between variation and genes?
➢ Variation •
Differences amongst individuals in a population (both in genes
and physical traits), that result from sexual reproduction.
➢ Genes •
Sections of DNA that code for particular traits
Populations of organisms have a variety of different genes. The
genes provide the variations where some are better suited to
certain environments than others.
➢
What is the relationship between
fitness
and survival of the fittest?
Fitness •
The combination of physical traits and behaviors that help an
organism survive and reproduce in its environment.
➢ Survival of the Fittest •
Individuals with characteristics best suited to their
environment survive.
Individuals in a population who have the best fitness
(best suited traits and behaviors) will survive.
What is the relationship between
natural selection and adaptation?
➢ Natural Selection • The process in nature that results in the most fit (best adapted)
organisms producing offspring.
•
3 steps: variation --> selection --> reproduction.
➢ Adaptation • The process that enables organisms to become better suited
to their environment.
Through the process of natural selection (variation -->
selection --> reproduction) , populations of organisms
become better adapted to their environment over time.
Influences on Evolution
Genetic Drift
Gene Flow
Mutations
Genetic Drift
➢ Genetic Drift •
Genetic change in a population, occurring in the absence of
natural selection, due to random, chance events.
➢ Examples of events leading to genetic drift:
-
mutation
-
chance dispersal
-
extreme weather conditions
Gene Flow
➢ Gene Flow •
Transfer of alleles (genes) from one population to another.
➢ Examples of events leading to genetic drift:
•
Migration
-
Immigration: organisms with certain alleles moving into a
population
-
Emigration: organisms with certain alleles moving out of a
population
Mutations
➢ Mutations
•
A change in the genetic sequence
-
they can affect anywhere from a single DNA building
block (base pair) to a large segment of a chromosome that
includes multiple genes
➢ Examples of events leading to mutations:
•
Random mutation during DNA replication or protein synthesis
•
Environmental factors such as sunlight, radiation, and smoking