Evolution of Australian Biota 3• Discuss examples of variation between

members of a species (syllabus)

• Identify the relationship between variation within a species and the chances of survival of species when environmental change occurs (syllabus)

Variation and Heredity• Variation refers to the differences in the

characteristics of individuals within a species. Eg offspring may resemble their parents but they are not identical to them.

• Heredity is the transmission of similar characteristics from parents to offspring.

Variation and Heredity

• Within a population, variation may have one of three origins: (i) genetic eg eye colour; (ii) environment e.g. body builders; (iii) a combination of genes and the environment e.g. the fur of many arctic animals changes to white when located in low temperatures.

• The ability of fur changing colour is hereditary but it is only operative in very low temperatures.

Survival of populations• The variation in the gene pool (all possible varieties) of a

population determines their chance of survival. • If there is a sudden change in the environment, individuals

possessing a variation (random) that is advantageous to the change are more likely to survive the changed conditions. Those that survive are more likely to reach sexual maturity and pass their favourable characteristics to their offspring. Individuals with less favourable variations will eventually be eliminated from the population (out-competed).

• If individuals within the population become so different

that they can no longer interbreed with individuals from the original population to produce fertile offspring, then the population is considered a new __________.

• For Example....• Let's say a disease sweeps through a population. Those

individuals with a natural resistance to the disease would survive.

• These ANIMALS have adapted to the new environment (i.e. they have adaptations which allow them to survive):

• Koalas in northern Australia have smaller bodies, shorter hair and a lighter coat colour than koalas in southern Australia. Larger mammals tend to survive better in colder climates due to having less body surface area compared with their volume so they can conserve heat more efficiently.

• Snow gum trees grow in the Snowy Mountains and as altitude increases the trees decrease in height, leaves become shorter in length and fruit increases in size and frost resistant

Survival of populations

Survival of populations

Survival of populations

Charles Darwin and Alfred Wallace• In 1858 Charles Darwin and Alfred Wallace proposed

their theory of evolution by __________ __________.

The theory centres around four main points:

1. Variation – individuals within a population that reproduce sexually, show variations that can be passed from one generation to the next.

2. Natural selection – selective pressure (change in the environment) puts constraints on organisms (eg resources become limited). These constraints are called selective pressures and determine which individuals are best suited to the prevailing conditions.

Charles Darwin and Alfred Wallace

3. Survival of the fittest – more individuals are produced within a population than can survive. Those individuals with favourable variations have a greater chance of survival because they out-compete those with less favourable variations. Organisms surviving reproduce and pass on their genetic variations on to their offspring.

4. Isolation – if a population is isolated from the original population, interbreeding will be prevented over a period of time. This is important for the evolution of a new species to occur.