There's nothing in the known history of life that suggests it has a purpose or direction. In particular, there's nothing to suggest that 3.5 billion years of evolution were just advanced preparation for the appearance of Home sapiens. That's why we say that evolution appears unguided and purposeless [Is "Unguided" Part of Modern Evolutionary Theory?]. And that's why anyone who says that life shows evidence of purpose is not being scientific.
Creationists aren't happy about this so they will go to extraordinary lengths to wiggle out of the inescapable conclusion based on solid evidence. The usual excuse is to postulate that god is very sneaky. He/she/it makes a huge effort to hide his/her/its manipulations so that it only appears that evolution is unguided and purposeless. The clever creationists aren't fooled by this sneaky god; they can detect its deception, but scientists can't.
But this isn't the only form of counter-attack. Creationists also like to argue that mutations are not truly random. They point out that there are mutational hotspots in the genome and there's a bias in favor of some mutations over other (e.g. transitions are more common than transversions). In most genomes, mutations are more common at sites where C is methylated.
All this is true and the results were discovered by scientists, not creationists. It's why scientists try to avoid saying that mutations are random; instead they say that mutations are random with respect to their ultimate usefulness. Sometimes we slip up for simplicity as when I said in my previous posting that mutations are "essentially random," although I added "Let's not get into quibbling about the meaning of "random."
Jonathan Bartlett (johnny b) is a computer scientist who has written a lot about mutations on various creationist websites. His latest is from Uncommom Descent: Responding to Moran – Is “Unguided” Part of Modern Evolutionary Theory?.
I am always aghast that in the 21st century people still make the claim that mutations are unguided. This is a hold-over idea from before the discovery of DNA, simply because some mutations were found to occur independently of selection.I haven't seen any evidence that average mutations are "geared for adaptive purposes." It certainly doesn't look that way when you compare the sequences of homologous genes in different species.
However, modern evidence has showed that mutations are actually in large part due to mechanisms geared for adaptive purposes, just like the rest of biology.
It still looks to me that the mutations underlying evolution are unguided.
Here's an example of somatic hypermutation where mutations occur much more frequently in a specific regions of the genome than they do in other regions of the genome. It occurs in the precursors of B cells.
To point to a simple example (and one that is even often used as definitive evidence of the efficacy of random mutations!) let’s look at the somatic hypermutation process in the immune system. When a new bacteria invades the body and causes an infection, the body must generate a new gene. So what does it do? It takes a close-fitting antibody gene and mutates it. Now, first of all, you should notice that the mutations only happen in the correct gene – the antibody gene. That’s 1,200 base pairs out of 3,000,000,000. But that’s not all – it also focuses mutations on the part of the gene that attaches to the antigen, not the part that signals the cell (because otherwise it wouldn’t signal the cell correctly). So, that’s roughly 600 base pairs out of 3,000,000,000. The mutation system is highly selective of the sites that it mutates, skipping over the cell signaling systems and focusing on the part that is specific to the antigen.This is essentially correct. The target region is rich in methylated cytidine and the developing B cells produce an enzyme called activation-induced (cytidine) deaminase that deaminates cytodine to produce uridine. Uridine is recognized as DNA damage so it is repaired but the repair enzymes are just as likely to substitute an A:T base pair as the original G:C base pair. This cause a mutation.
These mutations make no contribution to evolution since these are somatic cells, not germ cells. It is, however, an example of increased numbers of mutations targeted to a specific site so we should be careful not to say that mutations are randomly distributed in the genome.