- It has a clear function or purpose.
- It is as simple as it can be to fulfil that function or purpose - fitness for purpose.
- It achieves that function or purpose as efficiently as possible.
I'll illustrate this with something I found on a very pleasant walk in Mid-Wales a few weeks ago - puffballs.
Function or purpose. Puffballs exist to produce more puffballs. If someone can tell me what intelligence would make a tool solely for making copies of itself then I'd be grateful. To me, this seems like the purpose of something that doesn't have an ultimate purpose.
Fitness for purpose. Well, I suppose you have to accept that puffballs are good at producing other puffballs, otherwise there wouldn't be puffballs. In fact, like other forms of life, they are singularly good at producing copies of themselves. But why the complexity? They could make copies of themselves simply by splitting in two, the way, for example, most single-celled organism do. Instead, puffballs spend months as subterranean fungal threads until coming together to form the familiar fruiting body above ground, just to spread themselves around. The way they do this leads on to the next example of non-intelligence - efficiency.
Efficiency. Puffballs are just about as inefficient at producing puffballs as it possible to imagine. A typical fruiting body will contain billions of spores of which only one, in the lifetime of the organism, needs to become another puffball for the population of puffballs to remain stable. The entire fruiting body, save only for the thin outer skin becomes a mass of spores. Giant puffballs (Calvatia gigantea), which can be a foot or more in diameter and some have been mistaken at a distance for sheep, can produce 7x1012, i.e., 70 trillion spores from a single fruiting body. Each spore contains the complete genome of the species that produced it.
It puts me in mind of when we were kids and entertainment for the other snipes in our gutter and me was to try to hit a tin can on a post with a stone (well, hunter-gatherers need to hone their hunting skills). Incompetent cheats would throw a handfull of gravel. The reproductive aim of the giant puffball is vastly less efficient and vastly less competent than throwing a handful of gravel at the target. If every spore became a giant puffball, and each grew to average size and did the same, the number of their spores would exceed the number of suns in the known Universe and their offspring would weigh more than Earth.
Whatever is aiming these spores, the term 'incompetent' flatters it. It's as though it doesn't even know in which direction the target lies. Puffballs are massively inefficient, hugely unnecessarily complex and have a 'purpose' which seems not to be a purpose other than endlessly making puffballs.
Examining all these factors, creationists have concluded that puffballs were designed by a supremely intelligent designer.