"Biologists must constantly keep in mind that what they see was not designed, but rather evolved." So cautioned Nobel Prize winner Francis Crick, the co-discoverer of the structure of DNA.
Why did Crick feel it necessary to admonish his fellow biologists to resist the temptation to think that what they study was not designed? Well, perhaps because of phenomena depicted in videos like this:
One of the puzzling questions this video raises is how the complex of proteins which works in tandem with the DNA could have arisen in the first place. DNA produces the proteins but DNA can't work without them, so if DNA can't work without them how did it produce them? It's very puzzling.
Here's another question. DNA codes for proteins, but what is the source of information that directs the proteins to the proper regions of the cell or the body and then instructs them to build the structures they do? If DNA codes for proteins what codes for this information and where in the cell does this coding mechanism reside? Moreover, how is the information that directs the proteins mediated? How are the information translated into the action of the proteins?
One more question. DNA codes for proteins, but what is the source of the information that controls an animal's behavior? Where does that information reside and how is it passed from generation to generation?
These are baffling questions so we must just shove them aside and not think about them. Instead we should all close our eyes real tight and repeat after Professor Crick: "These things were not designed. These things were not designed. These things were not ..."