An “old chestnut” of a question, and one which agnostics and hecklers are fond of hurling at defenders of the authority of the Bible is, “Where did Cain get his wife?” To many who are not enemies of the Faith, such a question may cause an unnecessary anxiety. As Adam and Eve were the first human pair on earth, and by natural generation had three sons who are named—Cain, Abel, Seth—and there is no mention of any named daughters—it does seem as if there is a problem in knowing where the female came from whom Cain made his wife. In the genealogy of Adam, as the natural head of the human race, we are told that “Adam begat sons and daughters” (Genesis 5:4). How many sons there were, apart from the three named ones, and how many daughters were born to Eve we are not told. Thus, because they lived long before the Sinaitic Laws were given, there was no moral difficulty involved in the marriage of near relatives. With Cain, the course was obviously a necessary one as it was with his brothers—they married their sisters. As we have already seen, Abraham married his own half-sister, Sarah.
After the birth of Seth, Adam lived for another 800 years, and died at the age of 930. When Eve died we are not told, but if she lived as long as her husband, and she was able to continue procreation through the centuries, then the family of earth’s first pair must have been large indeed. The register of births and deaths in Genesis 5 is an instructive record of remarkable longevity. The name of the earliest patriarchs are given, and the long years each of them lived upon the earth. If you add together the years that each one lived, you will find that their united lives cover a long period indeed. Enoch lived for the shortest period, 365 years—a year for every day of our normal year; while Methuselah lived the longest period of any known man, namely 969 years—31 years short of a millennium. Adam lived for over one hundred years after the birth of Methuselah, and the latter would have been over 300 years old when his grandson, Noah, was born. There is little room for doubt that Enoch, the seventh from Adam, had the privilege of conversing with earth’s first man. By the end of the first two millenniums the population of the earth through direct intermarriage must have been enormous.
As there may have been a lapse of many, many years before Cain’s marriage, during such a period—130 years between the birth of Cain and Seth, the substitute for slain Abel—some of the unnamed sons and daughters of Adam and Eve were likely born. As there were no other humans on earth apart from their descendants, Cain, attracted to one of his sisters, took her to wife. Whoever the sister was who chose to go into banishment with her branded brother, she deserves credit for her willingness to share Cain’s curse and wanderings. It is significant that they called their first child Enoch, which means “dedicated,” and may suggest a change in Cain’s character. The word is akin to “train” as found in the phrase, “Train up a child” (Proverbs 22:6), and is also used in the dedication of a new house (Deuteronomy 20:5). Cain called the city he built after the name of his son “Enoch,” or “dedicated,” and, as Ellicott comments—
In old times the ideas of training and dedication were closely allied, because teaching generally took the forms of initiation into sacred rites, and one so initiated was regarded as a consecrated person. Though, then, the [Cain’s] wife may have had most to do with giving the name, yet we see in it a purpose that the child should be a trained and consecrated man; and Cain must now have put off those fierce and violent habits which had led him into so terrible a crime. We may add that this prepares our minds for the rapid advance of the Cainites in the arts of civilization, for the very remarkable step next taken by Cain—a fit spot where his offspring should dwell together in some dedicated common abode.