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MUTATION,
SPECIATION AND THE
RATE OF EVOLUTION
Chapter 5 sections 5.5 and 5.6
Mutations are random changes in the
DNA of an organism. When these changes
occur, entirely new genetic information can
occur.
Mutations can be caused by environmental
factors such as chemicals or radiation, or
from errors that arise when cells use or
make copies of DNA molecules.
www.bozemanscience.com/mutations
Neutral mutations have no immediate
effect on an individual’s fitness, or
reproductive success.
A harmful mutation reduces an
individual’s fitness.
A beneficial mutation gives an
individual a selective advantage.
Most mutations are neutral or harmful.
Sexual vs. Asexual Reproduction
What are some
advantages and
disadvantages to both?
How does sexual
reproduction lend itself to
evolution?
Darwinian evolution
Genetic mechanism
Inherited
characteristics
Inherited characteristics are determined by genes.
Organisms typically possess thousands of different
genes.
Population variability
Individuals of the same species differ from one
another, in part because they possess different
combinations of genes. The genetic makeup of all
individuals within a population is called the
population’s gene pool.
Source of new
variations
New traits can arise when genes become mutated.
Natural selection
Some genes determine traits that make the
individual better suited for survival and
reproductive success. Individuals with these traits
will produce more offspring, some of which will
inherit these advantageous genes.
Evolutionary change
Over many generations, individuals carrying the
genes that determine the most favourable traits for
survival and reproductive success will become more
common in the population. Evolution is this change
in the population’s gene pool.
Speciation is the formation of new
species.
Allopatric speciation occurs as a result
of populations being reproductively isolated
from each other. This is a three step
process.
1. A physical barrier separates a single
interbreeding population.
2. Natural selection works on the separate
groups independently.
3. In time, accumulated physical and/or
behavioural differences become so pronounced,
the populations can no longer interbreed.
The Rate of Evolution
The Theory of Gradualism suggests
that changes to species occur at a slow and
steady rate.
The theory of punctuated equilibrium
suggests that changes happen in a sudden
manner. This theory has three main
assertions:
1. Many species evolve very rapidly in
evolutionary time.
2. Speciation usually occurs in small
isolated populations, so intermediate
fossils are very rare.
3. After an initial burst of evolution,
species are well adapted to their
environment and so do not change
significantly over long periods of time.