It is difficult to analyze a complex process without taking it apart. The principle that a complex system can be understood by studying its component parts. Has been a powerful strategy in biology. For example, Watson and Crick deduced the role of DNA in inheritance by studying its molecular structure. The study of biology balances the reductionist strategy with the goal of understanding how the parts of cells, organisms and populations are functionally integrated.
Population increases geometrically while food supply increases arithmetically.
A mechanism of evolution is natural selection. Populations have the potential to produce more offspring than will survive or than the environment will support. Individuals with traits best suited to the environment leave a larger number of offspring. This increases the proportion of inheritable variations in the next generation. Organisms' adaptations to their environments are the products of natural selection.