29_Drawing Hands by EscherA “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.
In 1971, French biologist Jacques Monod noted,
The code is meaningless unless translated. The modern cell’s translating machinery consists of at least fifty macromolecular components which are themselves coded in DNA: the code cannot be translated otherwise than by products of translation.
The late British philosopher Sir Karl Popper wondered,
What makes the origin of life and the genetic code a disturbing riddle is this: the code cannot be translated except by using certain products of its translation. This constitutes a really baffling circle: a vicious circle it seems, for any attempt to form a model, or a theory, of the genesis of the genetic code.