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IB Biology 5.4
“Evolution is the cumulative change in the heritable
characteristics of a population.”
Not only is it something that can be observed, but it is a
change in the genetic code of the species
For humans, it is not a change we will observe in our
lifetime but studies are done on organisms with a short life
span and done by farmers in something called selective
The mechanism of evolution is called NATURAL SELECTION
– Charles Darwin and the Galapagos Islands
In nature plants and many animals produce large amounts
of seeds and eggs to assure the continuation of their
Fossil Record
Fossils provide evidence for
evolution as all the ones found
and studied were SIMILAR to
existing organisms
These similarities suggested that
the organisms changed over time
as the environments they lived in
changed and they became
adapted to the surroundings
Fossil sequencing matches the
expected evolutionary pattern
and plant fossils are older than
animal in aquatic and land fossils
Algae  fungi  Worms  Fish
Amphibians  Reptiles  Birds
Land Vertebrates
Selective Breeding
Domestication of animals
Breeding of required livestock
Egg laying hens vs jungle fowl
The process is called artificial
selection – choosing desired
traits and mating to acquire
more individuals with these
The breeding time is much
shorter than geologic time so
domestication shows
Homologous Structures
Some similarities between
structures are superficial –
the bird wing and the insect
wing – having the same
function but different
Structures that superficially
look different but are
structurally the same are
homologous – the bat wing
and the bird wing have the
same bone structure
These do not prove ancestry
or evolution but the
similarities explain evolution
Speciation and Variation
When some members of the
same species become
geographically separated,
(islands) the characteristics of
these divided populations
may undergo changes such
that they are recognized
differently and thus a new
Variation within a species can
develop as well if certain
traits allow camouflage of the
organism so they do not
become prey, these traits will
pass to the next generation .
Mutations – good and
Sexual Reproduction
and the combination
of the gametes
Meiosis ; 2n  n
Natural Selection
Occurs When:
* Variation is present
* Mutations and sexual reproduction occur
* Adaptations are made to the environment
* Many offspring are produced
Due to these situations, differential survival and
reproduction occur, these inheritances get passed
on to future generations and there is a
progressive change within the species.
 Using
your textbook, Thoroughly
explain the two examples of natural
selection – steps, methods and
 Peppered moths is another one you
can use!