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Evolution
Topic 5.4
Assessment Statements
5.4.1 Define evolution.
5.4.2 Outline the evidence for evolution provided by the fossil
record, selective breeding of domesticated animals and
homologous structures.
5.4.3 State that populations tend to produce more offspring than
the environment can support.
5.4.4 Explain that the consequence of the potential
overproduction of offspring is a struggle for survival.
5.4.5 State that the members of a species show variation.
5.4.6 Explain how sexual reproduction promotes variation in a
species.
5.4.7 Explain how natural selection leads to evolution.
5.4.8 Explain two examples of evolution in response to
environmental change; one must be antibiotic resistance in
bacteria.
Define evolution.
The process of cumulative change in the
heritable characteristics of a population
Fossil record
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Life which existed more than 500 mya was
very different from life today
Although oceans have been around for nearly
5 billion years, fish fossils have only been
found in rocks 500 million years old or
younger
None of our present top predators existed at
the time of the dinosaurs or before
Many living organisms today have no
identical form in the fossil record
(exceptions: sharks, cockroaches, ferns)
Conclusion: Life on Earth is constantly
changing
Selective breeding (artificial
selection)
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Breeders learned to choose the males and
females with the most desirable genetic
characteristics and breed them together
After many generations, breeders realized
that certain varieties had unique
combinations of characteristics which did not
exist before (accumulation of small changes
over time)
Artificial and not a driving force of evolution
in natural ecosystems, but can be used as
proof that evolution occurs
Homologous anatomical
structures
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Structures similar in
form and function but
which are found in
seemingly dissimilar
species
Ex. Humans, bats, and
whales all have
pentadactyl limbs. This
suggests that all fivefingered organisms
have a common
ancestor
Populations tend to produce more
offspring than the environment can
support
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Why are energy and nutrients vital to the
parents’ survival used to produce so many
excess seeds, eggs, and spores that are
never going to give rise to viable offspring?
Limited resources
Consequences of overproduction: a struggle
for survival
Competition for resources can lead to
adaptive behavior
Members of a species show
variation
Bacteria – very little variation; Why?
 Sexually reproductive organisms show
great variation; Why?
 Variation is closely related to how
successful an organism is
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Causes of variety
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Mutation
May produce genes which lead to diseases
 May produce an advantage, such as faster
growing rate or better camouflage
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Sexual reproduction
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Thousands of genes are mixed and
combined by meiosis and fertilization
Natural selection
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Overproduction of offspring with natural
variations
Individuals with poorly suited
characteristics tend to be less successful at
getting resources and have less a change
of surviving to maturity
Individuals with well suited characteristics
tend to be more successful at getting
resources and have a better chance of
surviving to maturity
4.
5.
The successful organisms have a
better chance to reproduce and to
pass on their successful genetic
characteristics to the next generation
Over many generations, the
accumulation of changes in the
heritable characteristics of a
population results in evolution
Examples of natural selection

Antibiotic resistance in bacteria
Medications which kill or inhibit the growth
of bacteria
 Often give to people who are not suffering
from a bacterial infection who may be at
risk for an infection
 Few bacteria survive one antibiotic so
another is given
 Bacterium can continue to change genetic
makeup through mutations or plasmid
transfer and becomes resistant
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Pesticide resistance in rats
Pesticides kills most rats
 Due to natural variation, a few rats are not
affected by the poison
 Resistant rats survive and reproduce
 To kill the resistant rats, a new pesticide
must be used
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