If you have ever found yourself wondering why you shouldn't marry your cousin, especially if your grandma was an X-ray technician, or, if you've got questions about quantum physics and the conscience, then you should read the following book summary and discussion questions.
Schrodinger, Erwin. (1944). What is Life?. New York, NY: Cambridge University Press 
Chapter 1: The Classical Physicist’s Approach to the Subject
All atoms perform “a completely disorderly heat motion” (pg.10) all the time. It is only in enormous assemblies of such disorderly atoms that the statistically probable patterns of behavior we call laws emerge. In this way, all the laws of physics and chemistry are thoroughly statistical.
All measurements of physical phenomena are inaccurate to some degree due to the disorderly motion of the atoms composing the matter that is being measured. The fewer the number of atoms, the more the random motion of a single atom impacts the inaccuracy of the measurement.
When an organism (ex. our own body) is enormous relative to the size of the single atoms that compose it, the integrity or orderliness of the structure of the organism is not significantly compromised by the disorderly motion of singular atoms.
Our brain and the sensory system of organs attached to it, all compositions of singular atoms, is mechanically capable of feeling, thinking, and perceiving. The very act of thinking is dependent upon an actual correspondence between the physically well-organized system of our body and the physical orderliness of the material we are thinking about.
Chapter 2: The Hereditary Mechanism
The “naïve physicist” mistakenly believes that “an organism and all the biologically relevant processes that it experiences must have an extremely ‘many-atomic’ structure and must be safeguarded against haphazard, ‘single-atomic’ events attaining too great importance.” (pg.19) We now know that an individual chromosome actually contains the full code-script that determines “the entire pattern of the individual’s future development and of its functioning in the mature state.” (pg.21) A change in a single atom could change this code.
Chromosomes not only contain the code for development they are “at the same time instrumental in bringing about the development they foreshadow. They are law-code and executive power – or, to use another simile, they are architect’s plan and builder’s craft – in one.” (pg.22) Organisms grow and develop through consecutive cell divisions – a process known as mitosis. During mitosis the set of chromosomes in the parent cell creates an exact replica of itself such that the parent cell divides into two identically coded daughter cells.
After reaching a particular point of maturity, an organism generates haploid cells through a process known as meiosis. During meiosis the set of chromosomes in the parent (diploid) cell splits such that only one half of the set is included in each of the two daughter (haploid) cells. The male gamete (sperm) and female gamete (egg) are kinds of haploid cells that together join in fertilization to become a diploid cell encoded with the joint code-script of the male and female gametes.
During meiosis individual chromosomes are in such close contact with one another that they occasionally “cross-over” and exchange parts. Certain properties are encoded at particular locations of a chromosome. A particular property and the location at which it exists is referred to as an individual gene or genetic code. Codes nearby one another represent properties that are less likely to be separated when chromosomes cross-over. Extended breeding experiments and direct microscopic inspection may be able to help us determine the size and location of individual genes as well as determine the probability that certain properties are inherited by offspring.
Chapter 3: Mutations
Darwin’s mechanism of natural selection does not act upon the material of inherited small and continuous genetic variations but instead upon the material of inherited discrete and abrupt genetic mutations. A mutation is a kind of jump from one form to another without passing through intermediate forms. This jump between forms ought to remind physicists of quantum theory wherein no intermediate energies occur between two neighboring energy levels of orbiting electrons.
During meiosis the chromosomes in the parent diploid cell are divided into the two daughter haploid cells. The mutation occurring in the parent diploid cell is localized such that upon cellular division it only appears again in one of the two haploid daughter cells. In fertilization the specific haploid cells (sperm and egg) that join together may or may not carry the mutation of the father and mother. When a “mutated code” conflicts with a “normal code”, mutations that visibly express themselves in immediate offspring are called dominant (rather than recessive) mutations.
Unfavorable recessive mutations can accumulate across generations and are more likely to eventually express themselves when close-breeding (or inbreeding) occurs.
If mutations occurred frequently and in bunches, unfavorable and favorable mutations would often occur simultaneously in the same offspring. The unfavorable mutations would undoubtedly compromise the favorable mutations to so great an extent that the organism would perish by the mechanism of natural selection. Instead, because mutations are rare, singular, localized events, it is possible for a favorable mutation to occur unimpeded and result in an improved organism preserved and propagated by the mechanism of natural selection.
The natural frequency of mutations can be artificially increased by exposing parents to the radiation of X-rays and g-rays. For this reason, “the injuriousness of a marriage between first cousins might very well be increased by the fact that their grandmother had served for a long period as an X-ray nurse.” (pg.45)
Chapter 4: The Quantum-Mechanical Evidence
We have said that the order and integrity of a system is protected against the haphazard or disorderly heat motion of the atoms composing it when the size of the system is enormous relative to the size of the atoms composing it. However we have also said that only a small number of atoms, namely those determining the genetic code inherited via chromosomes, determine the entire growth and development of an organism. How does this growth and development continue across generations mostly unperturbed by the disorderly behavior of the atoms that determine genetic code? Quantum theory can answer this question.
We know that the electrons orbiting an atom’s nucleus only orbit at discrete energy levels or shells. They never exist at any intermediate energies but instead quantumly jump between states of being. In this way, nature is not continuous. This discontinuity limits the number of possible configurations that atoms can take on when they bond to form a molecule. The disorderly motion of individual atoms is typically not sufficient to overcome the binding energies that stabilize the molecule in a particular configuration. A quantum leap (or “lift”) of a molecule from one stabilized configuration into another (a new “isomeric molecule”) due to the normal disorderly heat motion of atoms is highly improbable. A “lift” from one configuration into another can only be made more probable by increasing the temperature of the molecule, thereby further exciting the disorderly behavior of the atoms composing it.
Chapter 5: Delbruck’s Model Discussed and Tested
Schrodinger writes: “We shall assume the structure of a gene to be that of a huge molecule, capable only of discontinuous change, which consists in a rearrangement of the atoms and leads to an isomeric molecule. The rearrangement may affect only a small region of the gene, and a vast number of rearrangements may be possible. The energy thresholds, separating the actual configuration from any possible isomeric ones, have to be high enough (compared with the average heat energy of an atom) to make the change-over a rare event. These rare events we shall identify with spontaneous mutations.” (pg.56)
With only a small number of possible (isomeric) arrangements of atoms it is reasonably possible to encode all that determines the characteristics of an organism. For example, a permutation of length four characters composed of only dots and dashes (Morse code) can generate different specifications. When permutations of length four as well as one, two, and three characters are counted, different specifications are possible.
A spontaneous mutation is a jump from one molecular arrangement across/over (but not continuously through) some energy threshold to another isomeric arrangement. The “mutant” arrangement is less stable than the “normal” arrangement and is therefore more susceptible to further mutations.
Chapter 6: Order, Disorder, and Entropy
Thus far we have only described the structure of genetic mechanisms but have not described how it operates. It is very likely that any satisfactory explanation of how the hereditary substance actually works will require “other laws of physics hitherto unknown, which, however once they have been revealed, will form just as integral a part of this science as the former.”
Schrodinger writes: “…to reconcile the high durability of the hereditary substance with its minute size, we had to evade the tendency to disorder by ‘inventing the molecule’, in fact, an unusually large molecule which has to be a masterpiece of highly differentiated order, safeguarded by the conjuring rod of quantum theory. The laws of chance are not invalidated by this ‘invention’, but their outcome is modified. The physicist is familiar with the fact that the classical laws of physics are modified by quantum theory, especially at low temperature. There are many instances of this. Life seems to be one of them, a particularly striking one. Life seems to be orderly and lawful behavior of matter, not based exclusively on its tendency to go over from order to disorder, but based partly on existing order that is kept up.” (pg. 68)
An isolated inanimate system tends to (rapidly then slowly) decay into a permanently “dead, inert lump of matter” or “state of thermodynamical equilibrium” or “maximum entropy.” “From the earliest time of human thought some special non-physical or supernatural force” seemed to prevent living organisms from rapid decay. Now we understand that through eating / metabolizing food, we feed upon the “negative entropy” (negative disorder = order) outside of ourselves to counteract the “positive entropy” (positive disorder = disorder) occurring inside ourselves – “continually sucking orderliness from its environment.” (pg.73)
Chapter 7: Is Life Based on the Laws of Physics?
Schrodinger writes: “A single group of atoms existing only in one copy produces orderly events, marvelously tuned in with each other and with the environment according to most subtle laws. …it needs no poetical imagination but only clear and sober scientific reflection to recognize that we are here obviously faced with events whose regular and lawful unfolding is guided by a ‘mechanism’ entirely different from the ‘probability mechanism’ of physics. …Whether we find it astonishing or whether we find it quite plausible that a small but highly organized group of atoms be capable of acting in this manner, the situation is unprecedented, it is unknown anywhere else except in living matter. The physicist and chemist, investigating inanimate matter, have never witnessed phenomena which they had to interpret in this way.” (pg.79)
We witness order (encoded chromosomes) producing order (organism) all within the context of an ever-present disorder (random motion of atoms)
Epilogue: On Determinism and Free Will
Schrodinger writes: “According to the evidence put forward in the preceding pages the space-time events in the body of a living being which correspond to the activity of its mind, to its self-conscious or any other actions, are (considering also their complex structure and the accepted statistical explanation of physico-chemistry) if not strictly deterministic at any rate statistico-deterministic.” This does not necessarily contradict the concept of free will. Every conscious mind freely and willingly directs the motions of its body (the motion of atoms) to act in accordance with purely mechanical laws of nature. In this way, each of us can say: “DEUS FACTUS SUM (I have become God).” (pg.87)
Western philosophers tend to think of consciousness as something separate from the body, something akin to a “soul.” Consciousness is not separate from the body, consciousness is the singular existing thing. “…consciousness is a singular of which the plural is unknown; that there is only one thing and that what seems to be plurality is merely a series of different aspects of this one thing, produced by a deception…” (p.g89)
Are all the laws of physics and chemistry thoroughly statistical?
How close does Schrodinger come to describing what we now call DNA?
Why shouldn’t you marry your cousin, especially if your grandma was an X-ray technician?
How does quantum theory help us explain both molecular stability as well as spontaneous mutation?
Are we existing in a continuous or discontinuous world?
Why do humans not rapidly decay?
Can free will exist in a world of statistico-deterministic space-time events?
What is the conscience?