Evolution by natural selection Learning Objectives: Be able to define mutation. Be able to describe how natural selection works Be able to explain how evolution occurs via natural selection

Why might one population of butterflies be better than another? One population have an advantage This allows them to survive and reproduce

Genetic variation Individuals show variation Due to differences in the genes they inherit Variation is due to changes in the genes This is caused by a mutation to the DNA

Mutations Take place when cells divide If these changes happen in gametes (sex cells) it can affect the phenotype of the offspring – producing new variants Some mutations cause no changes Some mutations are so harmful that the organism dies Very rarely the mutation produces an adaptation making the organism better suited to its environment – an advantage

Evolution is the theory that living organisms change over time Natural Selection is the process by which evolution happens

Survival of the fittest All species have evolved from simple life forms starting 3 billion years ago Individuals in a species show wide variation Individuals with the characteristics most suitable survive and reproduce The alleles get passed on to the next generation If two populations become so different they cannot interbreed they are a new species

Imagine this species of animal is living in a part of the world.

In any population there will be variation between individuals.

Let’s imagine one group needs camouflage to catch prey.

Some individuals with certain characteristics are more likely to survive to reproductive age.

These individuals are more likely to pass their characteristics on to the next generation

Over time these characteristics will become much more common amongst the population.

In time individuals will be born with mutations that further benefit them.

Eventually the species will look quite different to its ancestors.

Let’s imagine the environment changes....

1

The environment has become a lot wetter...

Only animals with Fur Oiliness 5 or greater survive to reproduce...

2

The environment becomes warmer...

Only individuals with fur length 4 or shorter survive to reproduce...

3

The environment becomes drier...

Only individuals of size 5 or smaller survive to reproduce...

4

The only prey available to eat is armadillos...

Only individuals with Jaw Strength 6 or more survive to reproduce...

5

A dangerous predator spreads throughout the land...

Only individuals with camouflage score 5 or greater survive to reproduce...

6

The environment becomes colder...

Only individuals with fur length 5 or greater survive...

The changes in the arrangement of the foot bones of horses support Darwin’s theory of evolution by natural selection. Explain how the arrangement of the foot bones of Eohippus could have evolved into the arrangement of the foot bones of Equus [4 marks]

Answer variation (in size / number / arrangement of bones) (and) those with large(r) / few(er) bones more suited to running or run faster (on harder / drier ground) these survive and breed (so) genes / DNA (for larger / fewer bones) passed on Study tip: Mutation of gene  advantage to survival  breed  pass on genes

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