1. After mass extinction
1.1. huge number of new species appear in fossil record
1.1.1. Employee
1.1.2. Employee
1.2. this is natural evolution
1.2.1. natural selection
1.2.2. new organisms adapt to different conditions
1.3. But evolution happens all the time gradually as environments gradually change
1.3.1. natural cycle of new species appearing and others becoming extinct
2. Organisms in isolation
2.1. when a species is only found in one place it is 'endemic' to that area
2.1.1. eg Borneo - many new species are still found due to huge area of tropical rainforest
2.1.2. in Galapagos islands where Darwin formed his ideas about evolution there are many related but different species there have evolved through geographical isolation
2.2. can be in large areas eg Borneo or small areas
2.2.1. Mount Bosavi crater of extinct volcano in Papua New Guinea where organisms are trapped in crater so have evolved in different way to those outside the crater. Are many species found there not known to be found anywhere
3. Isolation and evolution= new species formed
3.1. there is genetic variery between members of the same population
3.1.1. if 2 populations become isolated from each other, they may live in different conditions and difference characteristics are selected for.
3.1.2. the 2 populations become so different they cannot interbreed successfully and a new species will evolve
3.2. Geographical isolation is most common way of isolation
3.2.1. eg an area of land becoming an s=island
3.2.2. eg Australian continent separated over 5 million years ago and marsupials became geographically isolated. Many types of marsupial evolved there. In rest of world other animals with more efficient reproductive systems evolved but in Aust marsupials remain dominant.
4. Speciation is ....
4.1. when a new species is formed
4.2. when species have evolved through natural selection
4.2.1. natural genetic variety in a population means it has a wide range of alleles controlling characteristics enabling organism to survive and breed but if a population becomes isolated different alleles are selected to help the organism adapt to the new conditions and enable it to breed in the new conditions