In 2009, a variant of Jane Austen's Pride and Prejudice appeared, differing from the original in many important respects. Titled Pride and Prejudice and Zombies, it described an alternative England, overrun by the undead. Her inhabitants – many trained in martial arts – were preoccupied with self-defense, and London was "quarantined by towering walls, and divided into sections by the King's army."

This variant is not a spontaneous mutant, but rather the result of intentional engineering, performed by the writer Seth Grahame-Smith. However, Pride and Prejudice and Zombies was not synthesized de novo: much of the narrative, together with the original chapter divisions, remains as originally written. The protagonist, Elizabeth Bennet, though familiar with the "joy" of painting her "face and arms" with the blood of her enemies, remains fundamentally unchanged: she is witty and self-confident, and sustains a complex romance with Mr Darcy. Similarly Charlotte Lucas, though infected by the "strange plague" and herself transformed into a zombie, retains her basic identity: she is Elizabeth's devoted friend and a proponent of practical marriages.

Pride and Prejudice and Zombies is in this sense a genetically modified organism, derived from the ancestral Pride and Prejudice by the introduction of new (genetic) material taken from the unrelated "monster" genre. A small-scale comparison of the two texts supports this idea: all Grahame-Smith's modifications have parallels with genomic modifications performed (or harnessed) by laboratory scientists. Here, I examine six classes (Insertions, Duplications, Insertions with Duplication, Replacements, Over-expression, and Gain-of Function Mutations) of these modifications, and draw parallels with biological examples.

Insertions

Insertions are the addition of new genetic material: for instance, the insertion of four cytosine nucleotides, CCCC, into the sequence AAAAAAAA creates a new, extended sequence, AAAACCCCAAAA. Insertions – particularly of whole genes – can impart new characteristics, such as turning laboratory mice green by inserting the jellyfish gene GFP (green fluorescent protein).

Numerous insertions distinguish Pride and Prejudice and Zombies from the ancestral Pride and Prejudice. Some concern minor points of style; most, however, are dramatic, introducing violence- and zombie-related themes not present in the original. In Chapter 10, for instance, Elizabeth declines an invitation to walk with Mr Darcy, Miss Bingley and Mrs Hurst. In the original, she cites aesthetic reasons – a concern for the "picturesque" – for her decision. In the modified text, by means of a sentence-long insertion, she in addition cites the likelihood of zombie attack.

Original Text:

"No, no; stay where you are. You are charmingly grouped, and appear to uncommon advantage. The picturesque would be spoilt by admitting a fourth. Good-bye."

Modified Text:

"No, no; stay where you are. You are charmingly grouped, and appear to uncommon advantage. The picturesque would be spoilt by admitting a fourth. Besides, that path is most assuredly rife with zombies, and I have not the inclination to engage in fighting them off to-day. Good-bye."

In several instances, foreign insertions are linked to the original material by means of a simple conjunction. In Chapter 1, as Mr Bennet replies with a laconic negative to his wife's gossip-related question – "have you heard...?" – an insertion, linked with the word "and," indicates his preoccupation with the zombie threat.

Original Text:

Mr Bennet replied that he had not.

Modified Text:

Mr Bennet replied that he had not and went about his morning business of dagger sharpening and musket polishing – for attacks by the unmentionables had grown alarmingly frequent in recent weeks.

The modified text also contains eleven large-scale insertions (three-quarters of a page or longer). Nine of these contain zombies (observations of or altercations with); the remaining two describe duels with (or with the secondary participation of) ninjas. These insertions add entire tracts of narrative not present in the original: Elizabeth removes a coachman's limb, then, with sword and musket, forces his coach through a zombie horde (Chapter 27); Elizabeth defeats three ninjas while blindfolded, strangling the first, beheading the second, and consuming the still-beating heart of the third (Chapter 30); Elizabeth visits the Oakham Mount "burning grounds" and observes wagonloads of caged zombies lowered into a pit of fire (Chapter 42), etc.

Duplications

A special type of insertion, the duplication, consists of the repetition of adjacent material. In the DNA sequence GGATCGG, for instance, duplication of the subsequence ATC creates a new sequence, extended by three nucleotides: GGATCATCGG.

Parallel changes distinguish Pride and Prejudice and Zombies from the original. For instance,as Charlotte becomes a zombie, her speech is marked by a stutter, communicated by means of duplicated letters. In Chapter 30, as Charlotte thanks Elizabeth for Mr Darcy's recent visit – in her absence, she asserts, he would not "have come so soon" – the letter c is repeated once and the letter w is repeated thrice.

Original Text: "...would never have come so soon to wait upon me."

Modified Text: "...would never have c-come so soon to w-w-w-wait upon me."

A second type of duplication, consisting of functionally equivalent words, is found in Chapter 25. Here, "Mr Darcy's estate," a synonym for "Pemberley," is introduced in addition to the original "Pemberley."

Original Text: Mrs Gardiner had seen Pemberley, and known the late Mr Darcy...

Modified Text: Mrs Gardiner had seen Mr Darcy's estate, Pemberley, and known the late Mr Darcy...

Insertions with Duplication

Some insertions, in particular those mediated by some viruses and by mobile genomic elements called "transposons," are accompanied by a duplication of sequence at the insertion site. Insertion, for instance, of the sequence AAAAAA into the sequence TTGCGTT, might result in a duplication of GCG, creating a new sequence, TTGCGAAAAAAGCGTT.

At least two such changes distinguish Pride and Prejudice and Zombies from the ancestral Pride and Prejudice. In Chapter 9, a note is sent from Netherfield to Longbourn requesting the presence of Mrs Bennet at the bedside of her sick daughter. In the original text, the words "the note was...dispatched" appear only once. In the modified text, these words appear twice, on either side of a short insertion describing a zombie attack.

Original Text:

The note was immediately dispatched, and its contents as quickly complied with.

Modified Text:

The note was immediately dispatched, but the rider was met with a group of freshly unearthed zombies on the road and dragged off to his presumable demise. The note was dispatched a second time with more success, and its contents as quickly complied with.

Chapter 38, which describes Elizabeth's journey from Hunsford to London, contains a similar set of changes. In the original text, the word "alarm" occurs only once. In the modified text, it appears twice, on either side of a 1-page insertion describing the devastation caused by a zombie attack on St. Ezra's Church.

Original Text:

Their journey was performed without much conversation, or any alarm; and within four hours of their leaving Hunsford, they reached Mr Gardiner's house...

Modified Text:

The first ten miles of their journey were performed without the slightest bit of conversation or alarm. But when they came upon the old white church in St. Ezra's Parish...Bodies lay everywhere: in pews; in aisles – the tops of their skulls cracked open; every last bite of their brains scraped out, like pumpkin seeds from a jack-o'-lantern...With no further alarm, they reached Mr Gardiner's house...

Replacements

In the laboratory, native genes are often replaced with foreign genes at the same chromosomal location. This can provide clues about a gene's normal function or expression pattern. Such changes can also occur on smaller scales. At the nucleotide level, for instance, replacement of AA with GGGG in the sequence TTTAATTT would create a new sequence, TTTGGGGTTT.

Many such changes distinguish Pride and Prejudice and Zombies from the ancestral Pride and Prejudice. In Chapter 2, for instance, as Mr Bennet prepares to inform his family about his recent visit to Mr Bingley, a reference to hat decoration is replaced with a reference to sword decoration.

Original Text:

Observing his second daughter employed in trimming a hat, he suddenly addressed her...

Modified Text:

Observing his second daughter employed in carving the Bennet crest in the handle of a new sword, he suddenly addressed her...

In Chapter 29, similarly, as Lady Catherine expresses astonishment at the Bennet sisters' unstructured upbringing, the office of family "governess" is replaced with the office of family "ninja."

Original Text:

"No governess! How was that possible? Five daughters brought up at home without a governess! I never heard of such a thing..."

Modified Text:

"No ninjas! How was that possible? Five daughters brought up at home without any ninjas! I never heard of such a thing..."

Overexpression

A gene's expression is controlled by a section of DNA called the promoter: strong promoters direct high expression and weak promoters direct low expression. In the laboratory, a gene's expression can be altered by modification of its native promoter, or, more commonly, by the introduction of a new promoter.

Higher than normal gene expression, or overexpression, can exaggerate a gene's normal effects. Overexpression of a growth hormone gene, for example, whose normal function is to promote growth, might create an abnormally large organism.

Multiple instances of overexpression occur in Pride and Prejudice and Zombies. In Chapter 48, as Mr Bennet outlines new expectations for his daughter Kitty, the temporal component of these expectations is 60-fold exaggerated. Ten minutes becomes ten hours.

Original Text:

"...you are never to stir out of doors till you can prove that you have spent ten minutes of every day in a rational manner."

Modified Text:

"...you are never to stir out of doors till you can prove that you have spent ten hours of every day in pursuit of your studies."

Numerous additional examples of overexpression concern emotion, transmuting feelings that are merely strong into feelings that are intensely violent. "Dislike," for example, is several times exaggerated: in Chapter 34, "deeply-rooted dislike" becomes "deeply rooted bloodlust;" in Chapter 44, "feeling a dislike against him" becomes "wishing to drink the blood from his severed head."

Similarly in Chapter 37, as Elizabeth reflects on Mr Darcy's marriage proposal, her emotions are also overexpressed. Her "indignation" against Mr Darcy is exaggerated to create a desire to murder him. Her self-reproach, equally exaggerated, becomes a complex ritual of self-mutilation, involving "seven cuts of shame."

Original Text:

When she remembered the style of his address, she was still full of indignation; but when she considered how unjustly she had condemned and upbraided him, her anger was turned against herself; and his disappointed feelings became the object of compassion.

Modified Text:

When she remembered the haughty style of his address, she dreamt of watching his eyes glaze over as she choked the life from his body; but when she considered how unjustly she had condemned and upbraided him, her anger was turned against herself; and she hastily applied her dagger to the seven cuts of shame, which had scarcely time to scab over.

Gain-of-Function Mutations

A gain-of-function mutation imparts a new or improved function to a native protein. Such a mutation might enable an enzyme to catalyze a reaction more quickly or to produce an entirely novel product.

Pride and Prejudice and Zombies is characterized by several gain-of-function mutations, often imparting a sexual function to a previously nonsexual word or section.One such mutation enhances the word "balls": in the original text, "balls" signifies formal dances, but in the modified text, "balls" obtains a second function signifying the testicles.

In Chapter 18 of the modified text, as Elizabeth dances with Mr Darcy at Netherfield, both functions are employed. Elizabeth, employing balls' original function, remarks, "Perhaps by and by I may observe that private balls are much pleasanter than public ones." Mr Darcy, employing its new, testicular function, replies, "On the contrary, I find that balls are much more enjoyable when they cease to remain private."

A similar gain-of-function mutation affects the word "intercourse." In Chapter 43, a journey to a region from an earlier period of her life leads Mrs Gardiner to reminisce about old experiences and to reinitiate a relationship ("intercourse") with an old companion. In the original text, the word is entirely platonic, but in the modified text additional cues – "she and her former lover" and "unbeknownst to the sleeping Mr Gardiner" – establish a new, sexual function.

Original Text:

...she was too much engaged in pointing out to her husband all the interesting spots in its environs to think of anything else.

...they had no sooner dined than she set off again in quest of her former acquaintance, and the evening was spent in the satisfactions of an intercourse renewed after many years' discontinuance.

Modified Text:

...she was too much engaged in pointing out to her husband all the interesting spots where she and her former lover had frittered away many a summer afternoon, before circumstances required the affair to be broken off.

...they had no sooner dined than she set off in quest of her former acquaintance, and (unbeknownst to the sleeping Mr Gardiner) her evening was spent in the satisfactions of an intercourse renewed after many years' discontinuance.

Final Thoughts

These six sections consider only a few of the classes of Grahame-Smith's modifications. Pride and Prejudice and Zombies is also marked by DNA inversions (in the form of transposed words and phrases), silent mutations (in the form of synonym replacements), and missense mutations (in the form of deliberately misspelled words), and so on.

The molecular techniques used by Grahame-Smith have also been applied to other works, enabling the production of a range of genetically modified texts: Android Karenina, The Meowmorphosis, Jane Slayre, and others. These modified texts possess new phenotypes. Some are merely new twists of humor, curious for their own sake, like a mammal engineered to possess fluorescent skin. Others, more utilitarian, render the text appealing to new audiences, like a plant engineered for cold-resistance, enabling it to grow at new latitudes.

The success of these variants – some commercial, some aesthetic – sets the stage for a new generation of literary geneticists, whose experiments will force the field in new directions. This new dynamic, converting the writing desk to a laboratory and the classic text to a model organism, may in addition pose its own ethical questions. We exist in a new era, exciting and disturbing, in which neither text nor genome is immutable, and in which humans, armed with new technologies, can force their evolution.