The doctrine of the serpent seed, also known as the dual-seed or the two-seedline doctrine, is a controversial belief in some fringe Christian or other Abrahamic religious movements that interprets the Biblical account of the fall of man as follows: the Serpent mated with Eve in the Garden of Eden, and the offspring of their union was Cain. Adherents believe this event resulted in the creation of two races of people: the wicked descendants of the Serpent, who were destined for damnation, and the righteous descendants of Adam, who were destined to have eternal life. The doctrine frames human history as a conflict between these two races in which the descendants of Adam will eventually triumph over the descendants of the Serpent.

Irenaeus (), an Early Church Father, condemned the notion of some people being naturally possessed of seeds of divinity in Against Heresies as a "Gnostic" heresy espoused by Valentinus (100–160). Valentinus did not, however, propose that there were children by Eve through the serpent or that there was a seed of the damned in contrast to the spiritual seed of the elect. The idea of the serpent having intercourse with Eve first appeared in medieval Jewish literature in Pirkei De-Rabbi Eliezer, written in the 8th century. However, this source does not contain the idea of a pervasive "serpent seed" existing later on—it merely accounts for Cain's evil.

During the 19th century, the full serpent seed doctrine was invented by Daniel Parker (1781–1844), who promoted the doctrine among Primitive Baptists and wrote about it in his book Views on the Two Seeds (1826).

This doctrine was embraced by American religious leaders who wanted to promote white supremacy. It was brought into teachings of British Israelism by C. A. L. Totten (1851–1908) and Russel Kelso Carter (1849–1928). Teachers of Christian Identity theology, which branched off from British Israelism, preached the doctrine during the early twentieth century and promoted it within the Ku Klux Klan, Aryan Nations, the American Nazi Party, and other white supremacist organizations. Some adherents of the doctrine use it to justify antisemitism or racism by claiming that Jews or members of non-white races are the descendants of Cain and the Serpent, who they variably interpret to be Satan or an intelligent non-human creature which lived before Adam and Eve.

The serpent seed teaching comes in several different forms. William M. Branham (1909–1965), Arnold Murray (1929–2014), Wesley A. Swift (1913–1970), and Sun Myung Moon (1920–2012) played important roles in spreading different versions of the doctrine among members of their respective groups throughout the 20th century. Around the world, there are millions of adherents of the serpent seed doctrine within Branhamism and the Unification Church. In 2000, there were an estimated 50,000 adherents of it within Christian Identity. The Anti-Defamation League and various Christian apologetics organizations have denounced racist versions of the serpent seed teaching by claiming that they are incompatible with the teachings of traditional Christianity, and they have accused promoters of them of exacerbating racial divisions by spreading hate.

Doctrine Various nuanced forms of the serpent seed doctrine have been developed over the centuries. In its most prominent modern form, it explains the biblical account of the fall of man by stating that the serpent mated with Eve in the Garden of Eden, and the offspring of their union was Cain. It claims that Eve had relations with Adam a second time, and Abel and his younger brother Seth were the two offspring who were produced by that union. Both of these events resulted in the creation of two races of people, the first event produced the wicked descendants of the Serpent who were destined for damnation, and the second event produced the righteous descendants of Adam who were destined to have eternal life. The doctrine frames human history as a conflict between these two races in which the descendants of Adam will eventually triumph over the descendants of Cain and the Serpent.

Genesis 3:14-15 is a foundational verse for the doctrine.

Variations of the doctrine claim that the Serpent's descendants have no souls because they are partially descended from animals and are therefore predestined for damnation. Some groups are markedly militant on the subject because of their millennial teachings, and as a result, they believe that at the end of days, a final battle will be fought in which the pure race will triumph over the impure race.

The identity of the serpent varies between groups. Some groups claim that the serpent is Satan himself, while other groups claim that the serpent is an animal which is either apelike or human-like. Some groups incorporate pre-Adamite views which state that the serpent was a non-human creature whose creation predated the creation of Adam.

The identity of the serpent's seed also varies between groups. Aryan Nations, an American anti-semitic, neo-Nazi and white supremacist group, claims that the descendants of the serpent are all people who are not of northern European descent. Other Christian Identity groups claim that the descendants of the serpent are either Jews or Africans. William Branham connected the serpent's descendants with Ham (the biblical progenitor of the African peoples), several Jewish figures, the highly educated, and society's criminals. Arnold Murray connected the descendants of the Serpent with the "Kenites", a group of people which he believed had infiltrated some part of Jewish society. In the Unification Church, the bloodline of all humanity is believed to be contaminated as a result of Eve's relations with the serpent. However, married couples can change their heritages by performing the Holy Marriage Blessing Ceremony which enables them to become the adopted children of their new Adam: Sun Myung Moon.Yamamoto, J. ISamu (2016). Unification Church. Zondervan.

Mainstream Christianity Mainstream Christianity rejects the serpent seed view. Many different Christian groups offer systematic rebuttals of the doctrine. For example, the Christian Apologetics and Research Ministry points to Genesis 4:1 in order to refute the doctrine. Because the biblical record explicitly names Adam as the father of Cain, the teaching of the serpent seed is considered incompatible with the Protestant teaching of Biblical infallibility.

Critics argue that the doctrine foments division and fuels racism, which makes it an unhealthy belief which is incompatible with Christianity because the belief itself leads to sin. One Christian apologetics group states, "Although an idea should not be criticized when it is wrongly applied, it is appropriate to condemn an idea when it logically leads to sin. A philosophy that teaches that some races or people are universally satanic, like the serpent seed doctrine, is one such philosophy." Also writing on the topic, Rev. John Brisby stated, "The Serpent's Seed doctrine is the hallmark of most radical hate groups today. Whether it involves neo-Nazis, right-wing militias, or one of the many other white supremacist groups, most of them share this doctrine in common. How do they justify their hatred towards Jews, non-whites, and others? They believe that these people are not real people at all!"

Other criticisms of the doctrine point out the theological repercussions of blurring traditional Christianity's interpretation of the doctrine of original sin. The serpent seed doctrine characterizes original sin as a feature of genetic inheritance rather than a spiritual condition. Mainstream Christianity teaches the belief that all human beings are equally sinful before God and incapable of redemption. Through faith in Jesus Christ, individuals can become children of God through adoption. The serpent seed doctrine undermines the basic teachings of Christian conversion by teaching the belief that only individuals who are descended from Adam are the inherent children of God, a belief which classifies them as the only people who do not need to convert to Christianity, while the Serpent's seedline is irredeemable.

History Early teachings The idea that Eve mated with the serpent, or Satan, and produced Cain, finds its earliest expression in the teachings of Valentinus (100–160), who promoted a doctrine which is similar to the serpent seed doctrine because it states that Eve mated with the serpent and produced Cain. In his teaching, the serpent was the manifestation of an aeon named Sophia who seduced Eve. The teachings of Valentinus were compiled in the Gnostic Gospel of Philip ().

A similar account is recorded in the Gnostic Apocryphon of John which was authored by the Sethians ().

Irenaeus recorded a portion of the teaching and denounced it as heresy in his book Against Heresies. Explaining and commenting on the teachings of Valentinus, Irenaeus states:

Medieval Judaism The teaching also appeared in medieval Judaica. In his 1957 book Cain: Son of the Serpent, David Max Eichhorn traces the belief that Cain was the son of the union between the serpent and Eve back to early Jewish Midrashic texts which were composed between 800 CE and 1200 CE. Eichhorn identified rabbis who wrote about the topic, including a 9th-century book titled Pirke De-Rabbi Eliezer and the Zohar. In their version of the serpent seed doctrine, Adam's first wife was Lilith and his second wife was Eve. Lilith became possessed by the spirit of God's wife and rebelled against Adam and became the mother of all demons. Eve was subsequently seduced by the serpent and became the mother of a race of evil men.

A later folk-version of the serpent seed doctrine was somewhat widespread in European Christianity during the Middle Ages and it ascribed the ancestry of legendary monsters such as Grendel to Cain.

The Aramaic text Targum Pseudo-Jonathan contains passages which refer to the serpent seed concept. The targum was referenced by Rabbi Menahem Recanati (1250–1310) in his Perush 'Al ha-Torah. The age of the writing is disputed. A 2006 analysis by Beverly Mortensen dates the Targum Pseudo-Jonathan to the 4th century and she regards it as a manual for kohanim.The Priesthood in Targum Pseudo-Jonathan: Renewing the Profession (Studies in Aramaic Interpretation of Scripture 4), Brill Academic Publishers, 2006 Gavin McDowell's analyses suggested that the document was created in the early 1200s because it includes excerpts from writings which date back to the 1100s.

In the Targum Pseudo-Jonathan, the serpent is an angelic being who is named Samael.

And again, in the Targum Pseudo-Jonathan..

So Adam knew his wife Eve/Hava, who desired the Angel (Samael), aka "The Serpent, Satan & The Destroyer" in Judaism & Talmudic Lore. And then she bore Kain. In one account Samael is also believed to be the father of Cain,Jewish Encyclopedia – Samael as well as the partner of Lilith. The relationship between Samael and Lilith is depicted in the Sigil of Baphomet, the official insignia of the Church of Satan.

Modern origins in British Israelism

British Israelism reintroduced a version of serpent seed beginning in the mid-1800s. A small circle of ministers in the United Kingdom first began to develop what they called "seedline" doctrine in the 1790s. The seedline teaching stated that two races of people lived upon the earth: a righteous pure seedline of people and an unrighteous impure seedline of people. The early teachings of the seedline doctrine did not offer an origin story for the two groups. The original form of British Israelism taught the belief that the Anglo-Saxons were descended from the lost tribes of Israel and were therefore part of the pure seedline.