Based on clues like these, biblical scholars speculate that the story of Cain and Abel was once an independent story that was attached to the story of Adam and Eve. The story of Cain and Abel presupposes that there were more people in the world than just Adam and Eve and their two sons. Unless there were neighbors around to witness the deed, why else would Cain be concerned about taking Abel out into the field to kill him? And why else would he be concerned about his safety when he was expelled from the community? It also explains how he was able to find a wife and need to build a city.
There’s another clue in the genealogies in Gen 4 and 5. Gen 4:17-24 gives a list of Cain’s descendants: Enoch, Irad, Mehujael, Methusahael, Lamech. The closing verses list the three sons of Lamech: Jabal, Jubal and Tubal-cain (and one daughter, Naamah). Vv. 25-26 describe the birth of Seth to replace Abel, and the birth of Seth’s son, Enosh (which means “man” in Hebrew).
Gen 5:1-32 begins with Adam begetting Seth and proceeds to Enosh, Kenan, Mahalalel, Jared, Enoch, Methuselah, Lamech, and Noah. Noah, it is noted, had three sons: Shem, Ham and Japheth. The name of the Seth line is eerily similar to the Cain line. Both genealogies end with the naming of 3 sons instead of the usual one. Biblical scholars believe that we have two traditions citing the line of descent from Adam, one through Cain and one through Seth.
The writing styles differ, too. The genealogy in Gen 5 follows a strict formula, just like the creation story in Gen 1 followed a strict formula. Biblical scholars attribute Gen 1 and 5 to the “Priestly” writer (or “P”) because of his interest in priestly matters like legal codes, genealogies and rituals. The genealogy in Gen 5 cites the name of the father, states he was X number of years old when he begat his first son, he lived Y number of years after that, and then after living X+Y years, he died. This formula is not broken except for Enoch who, instead of dying, was “taken by God.” If we only read Gen 5, we would have no indication that Cain, rather than Seth, was Adam’s firstborn son.
Compare this to the genealogy in 4:17-26 and it is a bit more free-form. We get details about the various accomplishments of the individuals mentioned: Cain built the first city, Lamech took two wives, Jabal was the ancestor of tent-dwellers, Jubal of musicians, and Tubal-cain of blacksmiths. A couple of wives and a daughter are also named. This genealogy is showing us how civilization and technology spread in the primeval period. Also, violence as Lamech brags about how he takes extreme vengeance on any who slights him in the least way. Lamech’s story prepares us for the increasing amount of sinfulness in the world that will lead God to want to destroy it in a great flood. Scholars attribute the author of this genealogy in Gen 4 (along with Gen 2-3) to the “Yahwist” writer (or “J”), who gets his name from his consistent use of the name YHWH for God.
Another difference between the two is that J’s genealogy does not provide ages for the various ancestors. P’s genealogy provides precise numbers and, using those numbers and others like them, we could calculate a date around 4000 BCE for the creation of the world. The problem for chronologists is that the numbers of years separating Adam from Noah are different depending on whether you consult the Hebrew Masoretic Text (1656 years), the Greek Septuagint (2242) or the Samaritan Pentateuch (1307). It quickly becomes apparent that the ages were not in the original text, but were added later.
It is also apparent that there is a desired number each tradition is aiming for and the ages are adjusted to meet that pre-determined date. One proposal, for example, is that the total of the years from the creation of earth to the dedication of the second temple in Jerusalem is 3600 according to the MT. When you consider that the Bible was edited during the Babylonian Captivity and the Babylonians used a base-60 mathematical system, 3600 is 60 x 60, a nice round symbolic number in base-60. Perhaps the numbers are different in the SP because they were counting to founding of the Samaritan temple on Mount Gerizim. We don’t really know for sure, other than that the numbers were definitely manipulated for some symbolic purpose.
The genealogies are considered by many to be some of the “boring” parts of the Bible, but there are some interesting aspects to them. Once you know where to look.