"The idea that living organisms were designed comes from a common belief that complex human-made things have been designed. But is this correct?"
In the way I believe, yes it is.
"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?"
Yes indeed they were. I highly doubt that silicon/metal/solder... All that goes into a cell phone was randomly thrown together and "Oh look what happened!", rather, people spent a long time researching radio technology and telephones in general to complete this final project. The word "evolve" has a base definition of any progressing change, technology does evolve in a sense, but this is irrelevant to the biological theory of evolution.
"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."
Absolutely.
"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."
Ok, to start off, True or false: someone made the first; 1)cell phone, 2) Airplane and 3)OS. Now, humans designed these through science, they did not leave these cell phones in a box for however many years and come out with a better one, did they?
"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."
Think of it as algebraic elements. Dos is E(1), W1 is E(2) etc... They needed those stages to get E(1, 2, 3, 4, 5) and finally! Win XP is here, did it evolve or was it designed? Can a small child, draw an accurate depiction of a human being? Not normally, when they grow older, however, they can. Did the small child evolve or did he grow and hone his drawing skills?
"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."
Well... Not to take this analogy too far, but there are many programs that never saw large market popularity, but are still hanging around today. The reason for that is that some people including the one who wrote it enjoy it. Think of it as building a tower, one needs the base blocks for building up, that doesn't mean that the top evolved. The top of this tower was designed, but the first part was needed.
"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."
I have no clue where you got that one. Were that true we would be living in caves not knowing how to write. I'm sorry, but that seems to be a highly flawed statement. Edison made a light bulb, he tried thousands of filaments, did it evolve? In a technological way, yes, but it had a design and a designer.
"So the conclusion is that all human-made complex things have been evolved and not designed."
No. They were designed and improved upon, imagine a house, the people build a porch on to it, the house is improved but it did not evolve.
"And if it is true from human-made complex things - why should it be wrong for the natural complex things (the living organisms)?"
Well, your argument follows an irrational logical process. Technology is more "improved upon" if you will, than "evolved". To see technological advancement, which is fully overseen by science and facilitated by research and very intelligent scientists and compare it to evolution is an analogy that is either false or beyond my scope.
Anyway, good luck in finding your answer.
"It is better to be silent and thought a fool than to open your mouth and remove all doubt" - Mark Twain
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