The debate about the validity of the theory of evolution continues among some individuals to this day. Although most members of scientific communities will agree that evolutionary processes are unarguably evidenced throughout the recorded history of mankind; many religious scholars believe that evolution is simply a theory based on assumptions.
The debate was perhaps sparked by the 1859 publication of The Origin of Species, by Charles Darwin. In this complicated and tangled web of scientific names, Darwin outlined theories that would become some of the most influential groundbreaking scientific concepts in history.
Not only does Darwin describe his belief that humans as we know them are a product of evolved primates, he also goes on to describe the processes by which he believes evolution to be possible. Natural selection, for example, is perhaps one of his best known evolutionary theories suggesting that animals who are most fit to adapt to the constantly changing environment will survive. By surviving, these organisms will generally tend to reproduce and generate more offspring than comparably "weaker" organisms within the same species.
Although Origin of Species continues to serve as the benchmark work in scientific evolution theory to date, many scientists have spent years analyzing Darwin's research and data in order to either prove or disprove his theories.
Overall, if evolution theory gets your heart pumping and you'd like to know more about rudimentary evolutionary theories, then definitely pick up Origin of Species at your local bookstore or library; however, keep in mind that most layman readers will generally be lost among the dense scientific materials and abstract theoretical concepts.