AQA B2.8 Speciation

No evolution is more B1 and no specific info on horses is needed. All you need to know is :
a) Evidence for early forms of life comes from fossils.b) Fossils are the ‘remains’ of organisms from manyyears ago, which are found in rocks. Fossils maybe formed in various ways:■ from the hard parts of animals that do notdecay easily■ from parts of organisms that have not decayedbecause one or more of the conditions neededfor decay are absent■ when parts of the organism are replaced byother materials as they decay■ as preserved traces of organisms, eg footprints,burrows and rootlet traces.c) Many early forms of life were soft-bodied, whichmeans that they have left few traces behind.What traces there were have been mainlydestroyed by geological activity.d) We can learn from fossils how much or how littledifferent organisms have changed as life developedon Earth.e) Extinction may be caused by:■ changes to the environment over geological time■ new predators■ new diseases■ new, more successful, competitors■ a single catastrophic event, eg massive volcaniceruptions or collisions with asteroids■ through the cyclical nature of speciation.Additional guidance:The uncertainty arises from the lack of enough valid andreliable evidence. if) New species arise as a result of:■ isolation – two populations of a species becomeseparated, eg geographically■ genetic variation – each population has awide range of alleles that control theircharacteristics■ natural selection – in each population, thealleles that control the characteristics whichhelp the organism to survive are selected■ speciation – the populations become sodifferent that successful interbreedingis no longer possible.