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. Thus, 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 (c. 180), 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 sources 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.