Here is a question I was asked recently. “When Cain was exiled, he said to God the punishment was too great, and he would be killed walking around by himself. But where did the other people come from? Wasn’t it just a family of four in the beginning?”

There are a few clues in the text that help us answer our question:

1. In Genesis 4:3 NKJV, the Bible reads, “And in the process of time it came to pass…” We are not told how much time passed between when we are first introduced to Cain and Able and when chapter four’s events occur. But, we can infer that it was enough time for these boys to grow into men and learn their respective trades of farming and shepherding. 
2. We know that people were long-lived before the flood. For example, we read in Genesis 5:32 that “Noah was five hundred years old, and Noah begot Shem, Ham, and Japheth.” 
3. Because Eve is called the “mother of all living” (Gen. 3:20), it is safe to say that she and Adam continued to have relations after the birth of Cain and Able (The fact that Cain and Abel exist points to them continuing to have relations).

So, where did the other people come from? They were the other children and grandchildren of Adam and Eve. This also explains why Cain had great fear because Abel wasn’t somebody they didn’t know. Abel was a beloved son, brother, uncle, etc., and Cain killed him.