speciations occurs when populations of the same species become so different that they can no longer sucsessfully interbreed to produce fertile offspring
isolation is where populations of a species are seperated
can happen due to a physical barrier eg floods + earthquakes
conditions on either side of the barrier will be slightly different
because of different environment, different characteristics will become more common in each population due to natural selection they are better adapted to their environment so they can have better chance of survival and reproduction
eventually individuals from the different populations will have changed so much that they wont be able to breed with one another to produce fertile offspring
diff species
alfred russel wallace
came up with idea of natural selection and published work with darwin
he realised that warning colours are used by some species to deter predators from eating them eg butterflies and that this was an example of a benificial characteristic that had evolved by natural selection