Transcript Link natural selection to evolutionx

Charles Darwin’s
Theory of Natural Selection
and its significance
as a mechanism of
Evolution
Linking Natural Selection to Evolution
• Darwin observed four things that happened in
nature, which meant that species could
change.
.
Natural Selection is based on Darwin’s
observations and deductions
• 1 Organisms produce more young than the
population needs to survive.
• 2 There is competition between individuals for
survival.
• 3 There is variation between individuals.
• 4 Some individuals are more likely to survive
and breed than others.
Student Task
• Your group needs to choose one of these
underpinning points and discuss why it is
central to allowing evolution to occur.
• Evolution is defined as a change in the allele
frequency of a gene pool over time.
• If there is no pressure to compete for the essential
resources, no individuals have an advantage over any
other individual. All will be able to breed and all
characteristics will be passed on to the next
generation. The population will not change.
• When some resource is in short supply, the
individual with the characteristic that allows it to
take that resource enough to breed will
have more
descendants in
the next
generation.
• Other individuals that cannot get enough of the
resource will die and their characteristics will not
be in the next generation.
How does this connect to the
definition of Evolution?
• The features that allow the parent to compete for
the resources are controlled by the alleles of the
parents.
• When these parents breed they pass their alleles
on to their offspring.
• More successful alleles will become more
frequent in the gene pool of a population.
• Less successful parents will not pass on their less
successful version of the gene, so that allele will
become less frequent.
Variation between individuals
is important because
• the parents with the most
favourable traits are able to
survive longer (because
they compete better for
the resources that are
limited).
• They survive longer therefore they are able to
breed and pass on their traits to their
offspring,
• Which allows the next generation to be more
populated by individuals who have inherited
traits that are competitive(better suited to
their habitat).
• Individuals with variations that are less
successful are less likely to breed and pass on
their variety to the next generation.
• This removes unsuccessful variants from the
breeding pool.
How does this connect to the
definition of Evolution?
• The individual variation is based on the alleles inherited in
the genes. A gene can have more than one version, called
an allele. The different alleles can sometimes cause
different phenotypes, or variations between individuals.
• If one phenotype is more competitive at getting resources
than another it is said to be more successful. This means
the successful phenotype will have more offspring and have
more of its type in the next generation.
• When more of one sort of allele appears in the next
generation, the frequency of that allele in the gene pool
has changed.
• This is important because then the favourable
traits are passed on to the next generation,
which means the next generation is more
likely to survive.
The suitability depends on the habitat.
3 different species with suitable
Characteristics for their habitats.
How does this connect to the
definition of Evolution?
The best suited characteristics are controlled by
the alleles inherited by the individual.
These individuals pass these alleles on to their
offspring.
These offspring are more competitive for
resources in the habitat so they will survive (and
reproduce).
The most favourable alleles become more
frequent in the gene pool over generations.
• It is important that not all young survive when
the resources are limited. It puts individuals in
the group under pressure to survive.
• A population can respond by having some
individuals migrate to a new area, which reduces
the pressure on resources. This allows the
population remaining to continue without
pressure.
• Individuals that are under pressure for
resources have to compete. The majority of
the offspring that survive will have the most
suitable characteristics to compete.
How does this connect to the
definition of Evolution?
• Those successful offspring have inherited the
successful alleles from their parents.
• If the unsuccessful variations in the offspring
die and are not passed on those alleles are
less and less likely to appear in the population
in the future.
• The frequency of the successful alleles and
unsuccessful alleles is changed over time.
• Another way of looking at it is that
This is important because if the offspring
could all survive, the only way a gene pool could
change is by chance.
This could mean that the gene pool didn’t fit the
environment.
The significance of Evolution
• is that the whole population becomes more
suited to the habitat they live in, by the process
of Natural Selection, over time.
• If the environment doesn’t change, the same
selection pressures continue to operate on the
gene pool and the same variations are successful.
• When the environment does change, new
selection pressures cause different variations in
the population to become more successful.