The genealogy of the time before the flood is given quite explicitly, until one checks back into the earlier documents. The Septuagint and the Samaritan versions have differences in their numbers. However for our purposes we will stay with the numbers in the usual English Bibles, realizing that there may be variations.
In table 1 which shows the people in this era their date of birth and death is given in Anno Mundi notation. That is to say the years are counted from creation. It is realised that there are problems with trying to do this, but some interesting facts appear, subject to the correct transmission of the data to our present Bibles.The children of God and the sons of men
The first thing noted from the listing is that there are two distinct lines listed. To use the terminology of Gen.6 we can call these the children of God, and the children of men. For the children of Men (the line of Cain) the list goes to the eighth generation and no ages are given.
Little is said of the people in this line. Information is given only for Cain and for the last two generations. The penultimate generation given is named Lamech. He is named as a polygamous man with two wives (who are named). He killed a man for hurting him and made up a poem about it to his wives.
We are given special information of three of his sons :
Jabal the father of wandering herdsmen
Jubal the father of musicians
Tubalcain the father of metal workers
(Note the way the word "father" is used here!)
For the children of God we are given more detailed information on their ages, and the list extends to Noah in the tenth generation. Enosh in the third generation is listed as being of the time when "people began to call on God". Enoch in the seventh was translated without seeing death. It is interesting to note that Noah was still childless when God first warned him of the flood. Shem, his eldest son, was born less than one hundred years before the flood.
In this line also a man in the penultimate generation was called Lamech. A quite different person from the Lamech in the other line. When his son Noah was born he chose that name saying, "Out of the ground that the LORD has cursed this one shall bring us relief from our work and from the toil of our hands." Gen 5:29 (NRSV) A completely different attitude from his namesake.
If the figures are accurate then Adam was still alive when Lamech (father of Noah) was born, and Lamech was over 60 when Adam died. We do not know how widely scattered the sons of God were, but surely they had contact with one another, and Adam's stories of creation and the fall would have been repeated, by him, to the following generations right down to Lamech. Noah thus could have heard these stories only second hand from many witnesses who heard them from Adam himself!
It is interesting to speculate why there are less generations listed for the children of men, but I do not see any clues.Lessons from genealogies
Perhaps the first lesson we can note concerns long lives and the consequences thereof. In the story of the entrance of sin, there is no comment on the length of life that would be allowed to man. The discussion is on the hardness of that life, and the fact that there would be death; access to the tree of life could not be allowed. However when the genealogies are studied a lot more information is given. There is still a very lengthy life span, at least for the children of God.
Though life spans are not given for the children of men, the limited number of generations listed leads to the assumption that their life spans are similar.
Knowledge grows over one's life, and knowledge is increased as it is shared. During this period of earth's history nine or more generations were alive at once. Today it is rare if more than four can be assembled for a picture, and in that case the older ones are beginning to lose their skills and abilities and the youngest generation is still in childhood. Imagine what could be learned with teams of so many generations working together. Yet the majority of the earth used this knowledge for evil purposes.
It is also interesting to contemplate how many people were living on the earth in the days of Noah, when wickedness was so rife that God desired to end it all. The Bible names one child in most cases and then says "he had other sons and daughters." For calculation purposes let us assume that each person had six sons and six daughters (we do not know how many there were, but I suspect this is a low figure). By the time of Noah there would be about ten million in his generation. Since most of the previous generations were still alive, that would give a population of almost twenty million! And this is probably a conservative estimate, it was probably higher.