Carnal relations with demons is pretty much the epitome of unsafe sex.  And they never call you. Clearly evil.  While that spontaneous, but unfortunate decision to go home with the person you met at the bar can lead to dire consequences such as sexually transmitted diseases or pregnancy (with a human child), knockin’ boots with your standard issue succubus or incubus is a far more insidious, dare I say infernal, proposition.  Incidentally, it’s a little bit ironic too (Oxford English Dictionary irony, not Alanis Morissette irony), given that much to the chagrin of the average fundamentalist Christian, medieval theologian, or witch hunter for the Inquisition, the motivation of the succubus or incubus has a startlingly evolutionary impetus.  Given that the standard textbooks on Christian demonology were written roughly four hundred years before Darwin’s Origin of the Species, it’s not especially surprising in historical context, but at least it’s funny now and an excellent conversation starter in Kansas, Oklahoma, or Texas.

One might think demons like incubi and succubi, loosed on an unsuspecting world, might just be looking to party.  Hell is likely not a barrel of laughs what with the ubiquitous fire, stink of sulfur and brimstone, pitchfork-based motivational techniques, and eternal torment, so a few days on Earth might seem like a pleasant vacation for the average imp.  Unfortunately for incubi (male version) and succubi (female version, although some theologians have argued that there are only incubui, and they are bixesual), when they drop in from the City of Dis, they are on the clock.  And if you think your boss is a slave-driver, try Satan on for size. The official job description for an incubi is to seduce a human woman, whereas the succubi is to seduce a human male.  While they are big fans of sin and reportedly an entertaining sexual partner, their purpose is more instrumental.  Succubi are not there because you are ethereally handsome.  Your mother was wrong.  Trust me.  Their main mythological purpose is to collect semen.  The semen is then passed to an incubus (or in some version of the mythos, the succubi simply then assumes male form) and is used to impregnate a human woman.  In a world where tasers and mace are common accessories and the logical sensibility that “no means no” is prevalent this seems like an awful lot of effort when there are so many other effective temptations a demon might implement for its nefarious purpose.  They must get “The Bachelor” in Hell.  They know what they’re up against.  “I mean, he gave me a rose and treated me like a princess, but he works for Beelzebub, and I just don’t think I can get past that…”.  So if the seduction thing isn’t about sin, what exactly is the purpose?  This is where irony rears its ugly head.  According to most demonologists in the past half-millennium, demons cannot reproduce by themselves.   They need to steal human seed, do demony things with it, and do an infernal equivalent of in vitro fertilization in order to procreate.  The child of such a union (mom is human, dad is a demon), is referred to as a Cambion, and by all accounts, they are strikingly attractive, tough, prideful, and most importantly, incredibly evil.

In Christian theology, we see an interest in the physics of this process as early as Augustine of Hippo, later Saint Augustine (354-430 A.D.), who mentioned the relations between incubi and human women in his City of God.

There is, too, a very general rumor, which many have verified by their own experience, or which trustworthy persons who have heard the experience of others corroborate, that sylvans and fauns, who are commonly called “incubi,” had often made wicked assaults upon women, and satisfied their lust upon them; and that certain devils, called Duses by the Gauls, are constantly attempting and effecting this impurity is so generally affirmed, that it were impudent to deny it. From these assertions, indeed, I dare not determine whether there be some spirits embodied in an aerial substance (for this element, even when agitated by a fan, is sensibly felt by the body), and who are capable of lust and of mingling sensibly with women (St. Augustine, De Civitate Dei, Book 15, Chapter 23)

By the time we get to Dominican priest and theologian Thomas Aquinas (1225-1274 A.D.), we have a robust description of the process of artificial demon insemination, as well as a practical justification in so far as the incubus/succubus combo has the sole purpose of procreating through stolen reproductive cells.

Still if some are occasionally begotten from demons, it is not from the seed of such demons, nor from their assumed bodies, but from the seed of men taken for the purpose; as when the demon assumes first the form of a woman, and afterwards of a man; just as they take the seed of other things for other generating purposes, as Augustine says (De Trin. iii), so that the person born is not the child of a demon, but of a man (Thomas Aquinas, Summa Theologiæ, Part 1, Question 51, Article 3)

The Malleus Malficarum (“The Witches Hammer”) was essentially the textbook on witches and demons in the 15th Century, primarily concerned with how to extract good confessions through effective waterboarding, and looking for ambiguous signs that would offer proof positive of involvement with demons.  Its primary author, Heinrich Kramer is best known, apart from this seminal text, for being the first to attempt a systematic persecution of witches in Tyrol.  Pretty much everybody in Europe had already dismissed witchcraft as superstition or as a minor crime, but somehow, Kramer managed to receive special dispensation from the Pope in 1484 to go hunt for witches and demons.  Most of his contemporaries (including the Bishop of Tyrol) though he was a senile nutjob.  After his papal endorsement, the Malleus Malficarum became wildly popular, as did the torturing and burning of witches, but by 1490 the Catholic Church condemned the Malleus Malficarum as false .  Talk about mixed messages.  At any rate, Kramer (and his co-author Sprenger—who some argue was just used as a big name to lend prestige to the book) had a lot to say about incubi and succubi.

But it may be argued that devils take their part in this generation not as the essential cause, but as a secondary and artificial cause, since they busy themselves by interfering with the process of normal copulation and conception, by obtaining human semen, and themselves transferring it….Therefore bodies which are assumed in this way cannot either beget or bear…Yet it may be said that these devils assume a body not in order that they may bestow life upon it, but that they may by the means of this body preserve human semen, and pass the semen on to another body….Secondly, it is true that to procreate a man is the act of a living body. But when it is said that devils cannot give life, because that flows formally from the soul, it is true; but materially life springs from the semen, and an Incubus devil can, with God’s permission, accomplish this by coition. And the semen does not so much spring from him, as it is another man’s semen received by him for this purpose (see S. Thomas, I. 51, art. 3). For the devil is Succubus to a man, and becomes Incubus to a woman. In just the same way they absorb the seeds of other things for the generating of various thing, as S. Augustine says, de Trinitate 3 (Malleus Malficarum, Part 1, Question 3).

By the 1600’s, not only do we have detailed descriptions, both physical and theological of incubi/succubi reproduction through human hosts, but an extensive list of historical personages who are assumed to have been a product of such a union.  It’s an impressive list of over-achievers.  Ludovico Maria Sinastri (1622-1701 A.D.) was a noted demonologist and Franciscan priest, advisor to the Inquisition, regarded by contemporaries as an expert in sins related to sexuality, and investigator of witchcraft, and devoted a great deal of attention to demon sexuality and reproductive techniques in his book De Daemonialitate et Incubis et Succubis (“Demoniality: Or, Incubi and Succubi”) which is thought to have been an important influence, if not the major framing document for the Catholic Inquisition throughout the 17th century.

In the above case, as well as in others that may be heard or read of occasionally, the Incubus attempts no act against Religion; he merely assails chastity. In consequence, consent is not a sin through ungodliness, but through incontinence. Now, it is undoubted by Theologians and philosophers that carnal intercourse between mankind and the Demon sometimes gives birth to human beings; that is how is to be born the Antichrist, according to some Doctors, such as Bellarmin, Suarez, Maluenda, etc. They further observe that, from a natural cause, the children thus begotten by Incubi are tall, very hardy and bold, very proud and wicked. Thus writes Maluenda; as for the cause, he gives it from Vallesius, Archphysician in Reggio :«What Incubi introduce in utems, is not qualecumque neque quantumcumque semen, but abundant, very thick, very warm, rich in spirits and free from serosity….from the testimony of various Authors, mostly classical, that such associations gave birth to: Romulus and Remus, according to Livy and Plutarch; Servius-Tullius, the sixth king of Rome, according to Dyonisius of Halicarnassus and Pliny the Elder; Plato the Philosopher, according to Diogenes Laertius and Saint Hieronymus; Alexander the Great, according to Plutarch and Quintus-Curtius; Seleucus, king of Syria, according to Justinus and Appianus; Scipio Africanus the Elder, according to Livy; the emperor Caesar Augustus, according to Suetonius; Aristomenes the Messenian, an illustrious Greek commander, according to Strabo and Pausanias; as also Merlin or Melchin the Englishman, born from an Incubus and a nun, the daughter of Charlemagne; and, lastly, as shown by the writings of Cochlceus quoted by Maluenda, that damned Heresiarch Martin Luther (Sinistrari, 1879, p53-55).

There are an awful lot of important historical figures in Sinistrari’s list, although he claims to be quoting a number of classical authors.  It definitely seemed like the standard thing to do in the classical Mediterranean world is that if you didn’t like somebody, you would claim that they were demon spawn, or rather half-demon spawn.  It seems we have discovered the ancient analogue for “Your mama is so…” jokes.  Now that you’ve seen the big names and excerpts from important historical sources related to the incubi/succubi, let’s get to the funny part.  If you can get behind the basic premise of “gene-centered” evolution, that is that an organism will evolve to maximize its inclusive fitness (the individual doesn’t matter all that much, rather the expression of common genes globally is the primary evolutionary goal), it becomes very easy to explain the somewhat anomalous (for demons) incubi/succubi behaviors in relation to their reproductive strategy.  They’re just trying to maximize the presence of incubi genetic material as represented in the general population.  It’s a very community oriented genetic strategy.  They can’t reproduce on their own, so they have established a symbiotic relationship with humans to ensure the reproduction of their “selfish” genes a la Richard Dawkins. (who, if the Inquisition had the same authority as in the 15th Century, would no doubt have been included in Sinistrari’s list as a Cambion – has anyone else noticed how close “Sinistrari” is to “Sinister”?).  How awesome is that?  Catholic demonologists support evolution!

At any rate the Cambion, the product of a swap of genetic material between a human and a demon is thought to be somewhat wicked.  In fact, rumor has it the actual Antichrist will be a Cambion.  Undoubtedly, you have not missed the irony that the author of the Christian apocalypse is the product of demon evolutionary strategies.  You can’t make this stuff up.  Or you can.  Write it in a book.  A few thousand years from now, maybe you can get a deity named after you.  Or at least a demon.  Charles Darwin observed, “What a book a devil’s chaplain might write on the clumsy, wasteful, blundering, low, and horribly cruel work of nature!”  Little did he know that perhaps the devils are subject to the same sort of evolutionary pressure as the rest of us.

Aquinas, Thomas. Summa Theologica. New York: Benziger Bros translation, 1947.
Augustine, Saint, Bishop of Hippo. The City of God. Edinburgh: T. & T. Clark, 1884.
Sinistrari, Ludovico Maria, 1622-1701. Demoniality; Or, Incubi And Succubi: A Treatise Wherein Is Shown That There Are In Existence On Earth Ratinal Creatures Besides Man, Endowed Like Him With a Body And a Soul, That Are Born And Die Like Him, Redeemed by Our Lord Jesus-Christ, And Capable of Receiving Salvation Or Damnation. Paris: I. Liseux, 1879.
Summers, Montague. The Malleus Maleficarum of Kramer and Sprenger. ed. and trans. by Summers. Dover Publications, 1948.