150 years ago science's understanding of life was very primitive compared to what we know today, hence it was viewed as being relatively simple. Yet even today science still has difficulty clearly defining it. How do we define life? How do we tell the difference between something that's alive and something that is not? Science has grappled with this problem over and over and still it seems that their answers are not satisfying. The fascinating thing is that although science has such a difficult time trying to nail it down, we all intuitively recognize life. Why is that?
When we think of the word "natural" what do we think of? Something untouched by human intelligence: plants, animals, streams forests, rocks or mountains. We have also been indoctrinated with the idea that life is natural, that it has been untouched by intelligence. Yet life is teaming with intelligent information. And recognizing that is the key to defining life.
Two of the things we need to look at are complexity and organization. Something can be complex and highly organized, but contain no information, and therefore does not have to be intelligently designed. Yet something can look completely random and be intelligently designed. The question is, at what point do we start to recognize that complexity and organization cannot be the result of natural processes? We can never say for sure that intelligence wasn't involved, but there should be a point in which we say, intelligence must be involved.