Cain's Wife

 

When Cain moved to Nod with his wife, there were other people; they were just other sons and daughters of Adam & Eve (Gen 5:4). 

 

We just assume Cain and Abel were the first two and only two at this time.

 

But Seth was born after Abel was killed, and that was when Adam was 130 years old.

 

It's very likely that Adam and Eve had had dozens of children by then, and four or five generations of grandchildren. And who knows how long it was after Abel's death that Cain was cursed; maybe it was thirty minutes; maybe it was thirty years.

 

If each couple had a kid every two years on average for 128 years (one year for A&E's first child, plus one year after Abel's death for Seth to be born), then by the time Seth was born and Cain moved to Nod with his wife, the Earth's population could have been around 21,000 people.

 

If the couples only had one child every 4 years, the population would still be a respectable 1354 people.

 

If the couples had one child every year, the population would be 240,983.

And, just for kicks, if every couple had twins every year, the population would be about 20.5 million.

 

No matter how you estimate it, I don't think Cain would have much trouble finding a wife, or someone to be afraid of, or someone to populate a city.