Biochemist Michael Behe introduced the concept of “irreducible complexity” with his 1996 book, “Darwin’s Black Box,” which made the case for the idea that there exists at the cellular level “a single system composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning.”
To put it more simply, irreducible complexity means there are things like the Flagellum motor that consists of multiple parts that must all come together simultaneously if it is to perform its intended function. Assemble it sequentially and it doesn’t work. Yes, that’s an argument for intelligent design.
Before you close your mind and move on, you might want to take a little more than three minutes to watch this amazing video from the aptly named Discovery Institute.