Complex systems biology (CSB) is a field of science that studies the emergence of complexity in functional organisms from the viewpoint of dynamic systems theory.  The latter is also often called systems biology and aims to understand the most fundamental aspects of life. A closely related approach to CSB and systems biology called relational biology is concerned mainly with understanding life processes in terms of the most important relations, and categories of such relations among the essential functional components of organisms; for multicellular organisms, this has been defined as "categorical biology", or a model representation of organisms as a category theory of biological relations, as well as an algebraic topology of the functional organization of living organisms in terms of their dynamic, complex networks of metabolic, genetic, and epigenetic processes and signaling pathways .   Alternative but closely related approaches focus on the interdependance of constraints, where constraints can be either molecular, such as enzymes, or macroscopic, such as the geometry of a bone or of the vascular system. 
One of the most important factors in the declining share of Christians and the growth of the “nones” is generational replacement. As the Millennial generation enters adulthood, its members display much lower levels of religious affiliation, including less connection with Christian churches, than older generations. Fully 36% of young Millennials (those between the ages of 18 and 24) are religiously unaffiliated, as are 34% of older Millennials (ages 25-33). And fewer than six-in-ten Millennials identify with any branch of Christianity, compared with seven-in-ten or more among older generations, including Baby Boomers and Gen-Xers. Just 16% of Millennials are Catholic, and only 11% identify with mainline Protestantism. Roughly one-in-five are evangelical Protestants.