Evolution is accumulative. For a good example of the evolution of a complex organ of which there is much information - look into the evolution of the eye.
http://www.don-lindsay-archive.org/creation/eye.html
The process has been replicated with computer simulations:
Quote:
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In an article in the May 8 issue of the international journal Nature, Richard Lenski, Charles Ofria, Robert Pennock, and Christoph Adami report that the path to complex organisms is paved with a long series of simple functions, each unremarkable if viewed in isolation. "This project addresses a fundamental criticism of the theory of evolution, how complex functions arise from mutation and natural selection," said Sam Scheiner, program director in the division of environmental biology at the National Science Foundation (NSF), which funded the research through its Biocomplexity in the Environment initiative. "These simulations will help direct research on living systems and will provide understanding of the origins of biocomplexity."
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Source -
http://www.nsf.gov/od/lpa/news/03/pr0351.htm
Here's the abstract to that paper:
Quote:
A long-standing challenge to evolutionary theory has been whether it can explain the origin of complex organismai features. We examined this issue using digital organisms—computer programs that self-replicate, mutate, compete and evolve. Populations of digital organisms often evolved the ability to perform complex logic functions requiring the coordinated execution of many genomic instructions. Complex functions evolved by building on simpler functions that had evolved earlier, provided that these were also selectively favoured. However, no particular intermediate stage was essential for evolving complex functions. The first
genotypes able to perform complex functions differed from their non-performing parents by only one or two mutations, but differed from the ancestor by many mutations that were also crucial to the new functions. In some cases, mutations that were deleterious when they appeared served as stepping-stones in the evolution of complex features. These findings show how complex functions
can originate by random mutation and natural selection.
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Source - Lenski, R., Ofria, C., Pennock, R., and Adami, C. (2003). The evolutionary origin of complex features.
Nature, 423: 139-144.
One of the major arguments of ID proponents is that of irreducible complexity. By that they mean that some items are complex to have evolve like our brains, the eye, bacterial flaggelum, blood clotting and so forth. The major flag carrier of this idea is Michael Behe, a biochemist from Lehigh University. Sorry for Mr. Behe but he is wrong.
The situation with Behe also shows how ideology can overshadow even advanced education.