key area 6 - evolution of species

evolution is the gradual change if species overtime which can lead to - a change withing a species - the production if a new species

a mutation is a random change to an organisms genetic material (DNA). Mutations are spontaneous and are the only source of new alleles. Mutations are therefore an important source of variation in population.

• radiation eg UV radiation, x rays • chemicals e.g mustard gas

new alleles produced by mutation can result in plants and animals becoming better adapted to their environment. Variation within a population makes it possible for a population to evolve over time in response to changing environmental conditions.

• species produce more offspring than the environment can sustain • natural selection or survival of the fittest occurs when there are selection pressures • the best adapted individuals in a population survive to reproduce, passing on favourable alleles that confer the selective advantage. • these alleles increase in frewuency within the population

sometimes evolution can result in the formation of new species. this process is called speciation

• speciation occurs after part of a population becomes isolated by an ISOLATION BARRIER. this can be geographical, ecological ( diff levels of abiotic factors eg pH) behavioural ( diff mating behaviours) • different MUTATIONS occur in each sub population • NATURAL SELECTION selects for different mutations in each group, due to different selection pressures. • each sub population evolves until they are so genetically different that they are two different species (SPECIATION)

• food species for us • important source of medicines • raw materials e.g wood