In a nutshell, here are some basic reasons to believe that Darwinism cannot explain all diversity of life:
1. Darwinian processes (random mutation and natural selection) have never been observed to actually produce new information. (by information, I mean something very specific… "complex specified information") And yet new information has to be produced somehow… first, to create the first single-celled organism, and subsequently to add new features, structures, and organs to yield new, different, more complex organisms.
2. Darwin and his contemporaries thought that the cell was a very simple unit. They were ignorant of the complexities within the cell. Modern technology has revealed a level of complexity within the cell that Darwin could not have imagined.
3. Michael Behe has demonstrated conclusively that the machinery inside a living cell is "irreducibly complex." That is, the various molecular machines within the cell cannot function at all EXCEPT in their present form. No evolutionary pathway to those machines exists because those machine won't function in any simpler form. Although many have tried to rebut Behe's arguments, all have failed, missing Behe's points entirely.
4. The cambrian explosion shows all body plans appear in the fossil record in a very short period of time.
What is the scientific evidence for any alternative theory of speciation other than evolution?
1. Presence of complex specified information within DNA suggests an intelligent cause based on what we know, from our experience, about how information is produced.
2. Presence of irreducibly complex molecular machines and integrated systems in biology suggests an intelligent cause based on what we know, from our experience, about how machines and integrated systems are designed by humans with intelligence.
3. The Cambrian explosion is more consistent with the idea of an intelligent cause than is Darwinism.