"The theory of evolution by cumulative natural selection is the only theory we know of that is in principle capable of explaining the existence of organized complexity"

This quote by Richard Dawkins is referring to the theory of evolution by natural selection, which is the procedure by which organisms adjust to their environment with time. This theory is the only one that is capable of describing the presence of complex, organized life forms. Natural choice works by choosing for qualities that are beneficial to an organism's survival and recreation, and with time, these traits become increasingly more complicated. This process is cumulative, indicating that the characteristics that are helpful in one generation are given to the next, and the procedure continues till the organism has actually adapted to its environment. This theory is the just one that can explain the intricacy of life in the world, and it is a fundamental part of the clinical understanding of the natural world.