the process of cumulative change in the heritable
characteristics of a population.
Macroevolution – the change from one species to
Microevolution – the change from one variation
within a species to another. i.e. – a Chihuahua
and a Great Dane
Evidence for evolution….
• Fossil record
• Selective breeding of domesticated
• Homologous structures
The Fossil Record
• Darwin first collected convincing evidence for biological
• Earlier scholars had recognised that organisms on Earth had
changed systematically over long periods of time.
• Because bottom layers of rock logically were laid down earlier
and thus are older than top layers, the sequence of fossils also
could be given a chronology from oldest to youngest.
• Today, many thousands of ancient rock deposits have been
identified that show corresponding successions of fossil
• Hundreds of thousands of fossil organisms, found in well-dated
rock sequences, represent successions of forms through time
and manifest many evolutionary transitions.
Microbial (procaryotic cells)
Complex (eucaryotic cells)
First multicellular animals
Vertebrates (simple fishes)
Ancestors of humans
Millions of Years
Since First Known
• Inferences about common descent are reinforced by
comparative anatomy. For example, the skeletons of
humans, mice, and bats are strikingly similar, despite the
different ways of life of these animals and the diversity of
environments in which they flourish.
• The correspondence of these animals, bone by bone, can
be observed in every part of the body, including the limbs.
• Scientists call such structures homologous structures and
have concluded that they are best explained by common
The pentadactyl limb
(b) Outline the evidence for
evolution provided by fossils (2).
• fossils show changes over time (in
• fossilized organisms are different from
• (yet) share features with existing
organisms / homologous structures;
• suggest common ancestry;
• show intermediate stages in evolution of
groups / missing link fossils;
Populations tend to produce more offspring
than the environment can support.
• The consequence of the potential
overproduction of offspring is a struggle
• More offspring are produced than can be
supported, therefore there is a struggle to
survive, where some live and some die.
Members of a
Explain how sexual reproduction promotes
variation in a species.
• Independent assortment
• Crossing over
• Random fertilisation
• Mate selection
Natural selection – the mechanism
• Since organisms’ traits vary, some
organisms are more adapted to survival
• When there is a struggle to survive those
with favorable traits tend to survive long
enough to pass them on.
• Those that have less favorable traits die
before being able to pass the traits on.
Explain how natural
selection leads to
• The Darwin–Wallace
theory is accepted by
most as the origin of
ideas about evolution
by means of natural
1854 - Wallace left Britain on a collecting expedition to the Malay
Archipelago (now Malaysia and Indonesia). He spent nearly eight years
in the region collecting almost 110,000 insects, 7500 shells, 8050 bird
skins, and 410 mammal and reptile specimens, including over a
thousand species new to science; some of his specimens can be seen
in the Sarawak museum.
His best known discoveries are probably Wallace's Golden Birdwing
Butterfly Ornithoptera croesus
The book he wrote describing his work and experiences, The Malay
Archipelago, is the most celebrated of all travel writings on this region,
and ranks with a few other works as one of the best scientific travel
books of the nineteenth century.
• In February 1855, whilst staying in Sarawak,
Wallace wrote what was to become one of the
most important papers on evolution.
• Wallace's "Sarawak Law" paper made a big
impression on the famous geologist Charles
• Soon after Darwin had explained his theory of
natural selection to Lyell (during a visit he
made to Down House in April 1856) Lyell sent
a letter to Darwin urging him to publish the
theory lest someone beat him to it.
• Darwin began to write ‘On the Origin of
• 1858 - the idea of natural selection
occurred to Wallace .
• He wrote out and sent his ideas to
Darwin, who he thought might be
• Darwin had already discovered
natural selection about 20 years
earlier, and was part way through
writing his "big book" on the
• Darwin appealed to his influential
friends Lyell and Hooker for advice.
• They presented Wallace's essay,
along with two excerpts from
Darwin's writings, to a meeting of
the Linnean Society of London in
• These documents were published
together in the Society's journal.
Explain two examples of evolution in
response to environmental change
• One must be multiple antibiotic resistance
• The peppered moth (Biston betularia) is
another good example!.....
Multi-antibiotic resistance in
• Variation: a bacterium gains a gene producing
resistance e.g. through plasmids or mutation
• Environment: doctors/vets use the antibiotic to
control bacterial infections
• Selection: favours the bacteria that are resistant to it
and kills the non resistant ones
• Reproduction: resistant bacteria reproduce
producing more resistant bacteria. Eventually most
bacteria are resistant
• Evolution: doctors/vets use a different antibiotic to
control infections repeating the process so evolving
multiply resistant strains.
The IBO assessment statements:
5.4.1 Define evolution.
•Evolution is the cumulative change in the heritable
characteristics of a population.
•If we accept not only that species can evolve, but also that
new species arise by evolution from preexisting ones, then
the whole of life can be seen as unified by its common
•Variation within our species is the result of different
selection pressures operating in different parts of the world,
yet this variation is not so vast to justify a construct such as
race having a biological or scientific basis.
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.
•Greater survival and reproductive success of individuals
with favourable heritable variations can lead to change in
the characteristics of a population.
•Aim 7: Computer simulations can be performed.
5.4.8 Explain two examples of evolution in response to
•one must be antibiotic resistance in bacteria.
•other examples could include: the changes in size and
shape of the beaks of Galapagos finches; pesticide
resistance, industrial melanism or heavy metal tolerance in