Evolution means 'a gradual change over time'
The names Charles Darwin usually springs to mind. He lived from 1809 - 1882. Scientists then realised that species can change over time but didn't really know why. Darwin, took all the various ideas about what happened and with his own research and ideas and came up with his theory of Natural Selection. He published his theory in a book called On the Origin of Species by Means of Natural Selection.
So, what's it all about then. Well, back to variety and variation. Let's think of a the ancestor of the giraffe. It didn't always have a long neck and was probably like a little deer. Now, a group of these animals would show some variation - they would all be slightly different. Maybe, some of them had a slightly longer necks than others. Can you see where this is going. Now, imagine that there is some sort of drought. The grasses die out but trees survive because they have longer roots. The giraffey things that have the slightly longer necks can reach the leaves on the trees and so they survive. The ones with the slighter shorter necks cannot and so die. This means that the ones that survive can breed and pass on their characteristics - alleles - to their offspring. This is Survival of the fittest. Over a period of time the population will change to have loner necks. Any species that haven't adapted to an environmental change will die out and become extinct.
It could also apply to predators. A lion has a litter of cubs. The strongest one has the best chance of surviving. Survival of the fittest.
Now, don't think that evolution is all to with animals in the past - you know, dinosaurs and all that.
Evolution is happening all the time! Rats are now resistant to a poison called warfarin.Warfarin is a poison that stops the rats blood from coagulating. When it was first used most of the rats died, but some survived because of variation - they were slightly different. These survivors bred and now all the rats are resistant.
Darwin, when on his travels to the Galapagos Islands noticed that the finches, a type of bird, on the different islands all kind of looked the same but they all had slightly different beaks. He worked out that originally they were all one population of birds on one island. Maybe a storm or something blew them all onto different islands. As the birds were originally slightly different due to variation then maybe as the islands were all slightly different then different birds would survive and breed on different islands. There is a lot of differences there eh?! Over time, these survivors on each island would breed and eventually become so different that they couldn't interbreed with birds from other islands.
Darwin, when on his travels to the Galapagos Islands noticed that the finches, a type of bird, on the different islands all kind of looked the same but they all had slightly different beaks. He worked out that originally they were all one population of birds on one island. Maybe a storm or something blew them all onto different islands. As the birds were originally slightly different due to variation then maybe as the islands were all slightly different then different birds would survive and breed on different islands. There is a lot of differences there eh?! Over time, these survivors on each island would breed and eventually become so different that they couldn't interbreed with birds from other islands.
Survival of the fittest.
They had become a new species - this is called speciation.
