In the argument for design, it can be said that the world is special in that it's artifacts as well as organisms are directed towards functionality; they are goal-directed. Functionality can be defined as the purpose of goal fulfilled by an object or person. This functionality goes to imply the existent of a conscious, and most times, intelligent, designer.

Functions and adaptions are often typical things that Christians will point to in order to prove God's existence such as the incredible structure of the human ear that enables us to hear speech and music.

However, the Big Bang Theory states that creation acknowledges functionality, but it is by natural selection - thus rejecting the idea of the intelligent designer.

An evolutionist would argue along the lines of humans secreting sweat to make our bodies stay cool. This happens now because of evolution and natural selection - not because of an intelligent designer, but because of billions of years and the survival of the fittest.

Lastly, there is also an argument that states that there is neither functionality nor a designer. It states that humans appeared in the environment without natural selection and by accident. This puts us as humans - the most natural model of complexity and design - as beings with no purpose.

I'll leave with a quote by John Henry Newman, a leader of the Anglican church in the 1800s, a believer of intelligent design: I believe in design because I believe in God; not in a God because I see design