Rupert Sheldrake, a British biochemist, is best known for his controversial hypothesis of "formative causation," or the idea that nature itself has memory. According to Sheldrake's theory, every system in the universe--molecules, cells, crystals, organisms, societies--reacts in similar or established patterns in response to invisible fields of influence. This is known as "morphic resonance." Sheldrake purports that the invisible field, known as a "morphic field," is where established patterns collect to influence a like activity that may be taking place contemporaneously. An example that he often uses to convey this idea more readily is that of crystallization; in his book The Rebirth of Nature, Sheldrake explained morphic resonance thus: "The development of crystals is shaped by morphogenetic fields with an inherent memory of previous crystals of the same kind. From this point of view, substances such as penicillin crystallize the way they do not because they are governed...