A “chicken and egg” problem is one where it isn’t possible to get “one without the other.” For instance, M.C. Esher’s famous “Drawing Hands” picture, where two hands are drawing each other, where we need one hand to create the other (and vice versa). Likewise, in order to have a self-replicating cell, we face another “chicken and egg” problem: We need DNA to create enzymes in the cell, but we need enzymes to unzip the DNA. Molecular biologist David Goodsell explains that this “is one of the unanswered riddles of biochemistry: which came first, proteins or protein synthesis? If proteins are needed to make proteins, how did the whole thing get started?” Harvard evolutionary biologist Richard Lewontin notes,
No living molecule [i.e., biomolecule] is self-reproducing. Only whole cells may contain all the necessary machinery for self-reproduction…. Not only is DNA incapable of making copies of itself, aided or unaided, but it is incapable of ‘making’ anything else…. The proteins of the cell are made from other proteins, and without that protein-forming machinery nothing can be made.