Lets give that a try:
In any population there is variation of heritable traits. Not all members of a population will successfully produce offspring due to environmental factors, such as limited resources, disease, sexual preferences and predation. Those members of the population with heritable traits and combinations of heritable traits most likely to confer a benefit within these environmental pressures are most likely to produce offspring, and pass these traits on. In this way beneficial traits become fixed in a population. This is called natural selection.
Variation of heritable traits is produced through mutation. Mutation changes the DNA responsible for such things as embryonic development, biochemical pathways, and disease resistance.
The combination of new variation due to mutation, and natural selection result in the process of evolution. Over time this process can produce a great number of species, with vastly different anatomy. In other words, biodiversity.