My husband, Joe THE accountant, is also reading through the Bible this year. He led a great devotional on Genesis 5 today. He did the math to answer the question, “Who was Cain afraid of when God said he would be banished to wander the earth?” Based on the ages and life spans of those listed in Genesis 5, Adam would have lived to see 8 generations! Methusaleh would have died in the year the flood began. Then, extrapolating even with conservative estimates on population growth, there would have been over a billion people on the earth by the time of the flood.
Some scholars believe, since the Hebrew word for Adam can also be translated “mankind,” that God may have continued to create other people after Adam and Eve. But based on the account in Genesis 5 and some fairly simple math, it appears that there was no need for God to continue to create people. Joe’s theory also answers the questions about the Nephilim in Genesis 6. I’m hoping he will write up the details of his explanation, complete with the chart. If he does, I will post it here.