Explain the process of evolution by natural selection

In a population, random mutations of alleles will produce variation. Some of these mutations might be really helpful for the organism that has them and helps them to survive in their environment better. This is known as 'survival of the fittest'. It may or may not cause a physical change in appearance e.g. a giraffe's long neck. For example, if there are a lot of tall trees that the giraffe ancestor liked to eat, the ones with the longer necks will get more food so will survive better than others and produce offspring. The offspring of this individual will inherit this advantageous allele and they will go on to produce offspring as well. Over time, this allele will begin to increase in frequency in the population until eventually, a new species will form that is genetically different from the ancestral one.