Critically assess the Teleological argument as proof for the existence of God

The Teleological argument states that the world was designed by a superior being (i.e God). There are various forms of the argument, one of which was created by St Thomas Aquinas in the 13th century. Aquinas used the teleological argument as his fifth and final 'way' when attempting to explain the existence of God. He stated that when observing nature, it is clear that organisms always behave in a way which producesa beneficial end. From this he inferred that this 'order' is down to two possibilities; it has either resulted purely by chance or by a designer.