Witnessedater:
Questions: Why aren't there any people walking around with a third arm sticking out of the top of their head? Isn't evolution random?
Questions like these are a clear indicator that your understanding of the current state of evolutionary biology might not be as complete as you would like. While certain aspects of organic life are random, evolution itself is not. Natural selection most definitely is not random but rather predictable and thus falsifiable. Mutations are neither "good" nor "bad," in fact the vast majority are neutral. They only take on beneficial or deleterious characteristics in context with the organism's environment. A mutation (or, often, cumulative series of mutations) only imparts benefit if it helps the organism in its pariticular setting. When that happens, those organisms have an advantage and can come to dominate a population. THis is essentially how antiobiotic resistance in bacteria work.
Ah, yes, you might say, but it's still a bacteria. Well, of course. To find out if an accumulation of changes can (over time) trigger speciation, we have to look to the fossil record. And an honest appraisal of that might surprise you. Kathleen Hunt provides a pretty good overview here . Or at least read Prothero's Evolution: What the Fossils Say and Why it Matters.
One of the biggest challenges for creationists right now, IMHO, isn't the fossil record (though it's pretty solid) but the genetic record. Gene sequencing of ancient DNA means that genomes of humans, chimpanzees, Neanderthals and the latest find, Denisovians can be laid side by side. It becomes very easy to see that humans are pretty homogenous and that Neaderthals and Denisovians fall outside the range of modern human genetic diversity.
Finding that the human evolutionary tree is more of a bush? Cool. Trying to fit it all into the last 6,000 years? Impossible.