As usual, there is someone who has done a much better job scientifically, which is still easy to read, on this subject. It's worth reading mine because I'm a Christian who believes the Bible is inspired, despite being open to compelling and conclusize scientific evidence. However, after reading this page, the page at overwhelmingevidence.com is worth reading.
One of the big arguments between evolutionists and anti-evolutionists is over common design vs. common descent. We know, for example, that the wing of a bat, the arm of a human, and the fin of a dolphin all have the same basic structure (including dual forearm bones and finger bones). Is this because all three species have a common ancestor or is this because they have a common Designer?
Those who do not believe in common descent argue that just as a Chevy and a Chrysler, or even a Chevy and a Harley, have many similar parts, they have obviously not descended from one another. They have similar parts due to a similarity in design.
However, talkorigins.org put up a page from Dr. Edward Max arguing against the common design theory. He suggested that there are errors in design that are indicative of descent rather than design. For example, when cars switched from a carburator to fuel injectors, car designers did not leave a broken carburator in the engine. Biological entities, however, do not have this option.
Dr. Max's page was one of the strongest arguments I have ever seen for evolution. You probably know that Vitamin C is a vitamin because our body needs it but can't produce it. If we don't eat vitamin C we will get scurvy and eventually die. This is not true of most mammals, though, because most mammals have an enzyme, called GULO, that produces vitamin C in their body. Only primates, such as chimps, gorillas, orangutans, and humans, require vitamin C and one rodent, the guinea pig.
Oddly enough, both primates and the guinea pig have the gene to produce GULO, but it's broken in both. If the similarities between chimpanzees and humans are due to common design rather than common descent, just why would God bother to put the GULO gene in us at all? Why wouldn't he just leave it out rather than put a non-functional gene in us?
Really, the same truth applies to the fin of a dolphin and the human arm. There are a lot of other bone designs that would work for a fin. In fact, all fish have a different design. Only air-breathing mammals such as whales and dolphins have fins designed like our arms. If similarity in design was the point, why didn't God design dolphin fins like fish fins or shark fins rather than like a human arm? What sense does that make?
There is a web site that defends common design despite Dr. Max's arguments. I didn't find it's arguments at all convincing, but it did have one interesting point. It quoted Dr. Daniel Criswell of ICR as saying that even if the GULO gene is really broken in us, it could have happened since Adam. It's a common theory of young earthers that we have been “devolving” since Adam. It's interesting, though, that it only happened to us and our closest relatives.
I need to address here the fact that it also happened to guinea pigs. The page I mentioned earlier mentions that guinea pigs have their GULO gene broken much differently than the way primates gene is broken. There's a much different code sequence. The primate “pseudogenes,” on the other hand, are very similar. The web site says:
If a primate is no longer making GULO, we might expect mutations to accrue at a somewhat steady rate. Thus, not only should primates have a similar pattern of mutations, but the primates that we believe are more closely related (such as chimps and humans) should have more mutations in common with each other than they do with other primates. This is the pattern we see.
In response to those who argue that the GULO gene broke individually in all these species, just by chance, he writes:
It is extremely unlikely that we would see a pattern of mutations that forms what looks like a family tree simply by chance.
It always amazes me how the very people who say that evolution couldn't have happened by chance then go on to appeal to wildly unlikely chances wherever they need to do so. Evolution is not based on chance, by the way, but on survival.