The concept that some differences between species are too complex to have come about without having been designed is known as irreducible complexity.
One specific theory which accepts this concept and attempts to explain how God was involved is the Intelligent Design Theory.
However, the term 'intelligent design' has a broader usage than that given in the Intelligent Design Theory. It can refer simply to the belief that God designed the universe, without any specific claim as to how or when he did so. Many people consider this belief entirely compatible with standard Darwinian evolution, with no divine intervention -- life could be produced by a purely natural process, evolution, designed by God. God might merely have written the laws of physics, or chosen the fundamental constants, and left the universe to run like clockwork afterwards. Not all people who believe that God was involved in the design of the Universe also adhere to the specifics of Intelligent Design theory as proposed by Creationists.