The idea that living organisms were designed comes from a common belief that complex human-made things have been designed. But is this correct?
Let's see examples of the most complex human-made things like: modern Nokia mobile phone, Boing 747 airplane, Windows-XP operating system, and let's asks the following question: have these very complex systems been designed?
It is not easy to trace the history of living organisms emerging on earth and to prove if they were designed or evolved, as it is not possible to find all the required evidences.
But for the human-made things the history of their emergence is well known.
If one looks at the history of the above mentioned human-made complex things, it becomes obvious that all of them have been evolved. Airplanes, mobile phones, computer products have been evolved step-by-step, by trial-and-error method. No single human and even not a huge group of humans is able of designing a complex thing that never have existed before. Any complex thing appears upon a base of another complex things that already exist.
The most intelligent persons like Leonardo Da Vinchi, Newton or Aristotle could never have designed an airplane, a mobile phone or a computer program. And Bill Gates with his team could not have designed Windows XP in 1981, when they created DOS.
And not because of the short of intelligence or small amount of people. In order to appear, Windows XP required a long series of steps, where the product of each step had to be checked by the environment: the market. Lots of computer programs improved by small changes, then were exposed to the market and those which survived became a basis for the future programs. This is the only way that could allow Windows XP to appear.
All inventions in the world are actually very small steps based on something that already exists. No invention can create something much more complex than currently existing.
So the conclusion is that all human-made complex things have been evolved and not designed.
And if it is true from human-made complex things - why should it be wrong for the natural complex things (the living organisms)?