A population is a group of individuals
of the one species that breed together
in a particular environment.
E.g. 3 x groups of Rosellas (Adelaide,
Yellow & Crimson) are known as
subspecies. Reveal overlap in
distribution leading to their gradual
Individuals in one population are
members of the same species and
form a “breeding group”.
The gene pool of a population is the sum of all
genes of all the individuals in a population
Changes in gene pool can be brought about by
Mutations- Changes in the organisms DNA are
rare and unlikely to be beneficial
Natural Selection- Is the most important
process during evolution and is the cause of
change in the gene pool of the population
Gene flow- Is the exchange of alleles between
populations, which leads to diversity
Variation is essential for the process of evolution to
occur. The extent of this variation will be
determined by whether the species reproduces
asexually or sexually.
Mutations provide the only source of variation.
While mutations are still the only way that new
alleles arise, meiosis and fertilisation ensure new
combinations of genes and chromosomes are found
in offspring compared to their parents
Theory of Evolution
- All life forms have evolved from a
single, simple common ancestor
- That species change over time
- Can be recognized in a species by the
changing frequencies of genes in
1859 “On the Origin of Species”
Evolution was due to natural selection. Nature
or the environment (biotic and abiotic) selected
individuals who were best adapted or the fittest
“survival of the fittest”
This variation gave the organisms a reproductive
advantage enabling offspring to survive
The evolution of species in general is an extremely
slow process but there are exceptions.
Strong selective pressures leading to changes have
been observed over a short period of time.
I.e. Biston betularia
Over a period of 80-100 years of industrialization
the light coloured species became visible to birds
as tree trunks became darker with soot.
However the rare darker species now had the
distinct advantage due to change in its abiotic
Other examples include the rabbit population
and the “myxoma” virus.
Natural selection soon favoured those rabbits
which suffered a milder form of the virus.
As a result commenced reproducing at a faster
Resistant strains of bacteria
Some bacterial strains are resistant to specific
antibiotics as they have a genetic makeup that enables
them to survive exposure to that antibiotic.
Individual variation exists between bacteria, with some
being more resistant to certain antibiotics than others.
Antibiotics act as selective agents and those bacteria
that have the resistant gene are more likely to survive.
Over time, by the process of natural selection, there is
an increase in the frequency of the gene for resistance
to specific antibiotics.
Speciation is the name of the process that gives rise
to the origin of new species.
It is caused by geographic isolation such as
seas, lakes, mountain ranges, grasslands, deserts,
separating and isolating groups of individuals from
one another, preventing flow of genes.
Over time this will lead to significant differences
developing. These subspecies are now
Geographical isolation caused by the movement
and separation of continents over 250 million
years have led to the reproductive isolation and
unique evolution of Australian flora and fauna.