Irreducible complexity is the concept that certain biological systems are an 'all-or-nothing' deal; if just one element is taken away then the entire process would cease to function. Irreducible complexity is a popular argument against atheism, seeing as systems that are irreducibly complex could not have arisen by Darwinian evolution. Furthermore, the degree of complexity present in biology points to an intelligent designer - no one would believe that a cell phone could be the product of randomness and chance, yet organisms are exponentially more complex than any machine made by man.