Originally posted by IntaminFan397
First you say that the evolutionary process takes billions of years, then you say that an organism can randomly develop a mutation in it's lifetime, then that mutation continuously pop up (if beneficial) in the offspring. Either mutation is essentially evolution, or it isn't. If it isn't, then it's irrelevant to this discussion, but if it is, then your first statement is incorrect.
First you say that the evolutionary process takes billions of years, then you say that an organism can randomly develop a mutation in it's lifetime, then that mutation continuously pop up (if beneficial) in the offspring. Either mutation is essentially evolution, or it isn't. If it isn't, then it's irrelevant to this discussion, but if it is, then your first statement is incorrect.
Mutation isn't evolution, it is one of the ingredients necessary for it to happen. A mutation can occur randomly, and as I believe it's been agreed, if it's a positive change it will, theoretically, continue to occur in the offspring. HOWEVER, a mutation is not, in itself, evolution.
The evolutionary PROCESS does take billions of years. Until said mutation has become present enough to differentiate between an original population and the "mutated" population, it isn't recognized as evolution. Until then it's simply a trait.
Like Coasterkid said, geographic boundaries help A LOT with that happening. Geographic boundaries aren't necessarily required for it to happen, but they do tend to be a major factor in why you find, say, one species of primate in one location, and another species in a different. Such as primates on South America and Africa: they were probably the same "group" and then when those two continents separated, the populations got split, and then evolved in different directions. Or say why Capybaras are able to be so large in the abundance of the Amazon, yet field mice are small in the less-fertile plains, but they are both rodents.
Oh, and about your whole "complexity" issue. If you can accept that mutation is the basis for evolution, couldn't you accept that a mutation could occur that affects the the structure of a creature? Maybe, say, a mutation that says "I want more nerves in this location" and as that happened over and over again you all of a sudden have eyespots, then even further along you get a brain, and then further you get an entire nervous system?