Sailorboy.....

Cain was afraid of the Neanderthals that were outside the Garden. There is now scientific evidence that Homosapeins and Neanderthals co-existed. When Cain left the Garden he went and lived in the land of Nod,east of Eden. ....and he got married and had children. Cain was long gone, living in a city he built and named after his son (Enoch) and had kids and grandkids, before Adam and Eves next child was born. They named him Seth.
Eve said, "For God hath appointed me another seed instead of Abel, whom Cain slew."
Recent evidence shows traces of Neanderthal in much of our population living today.

The first word for man in the old testament can be translated man, mankind, or species. So translated Gen. 1:26, could read....Let us make (man, mankind, or species) in our own image. So when God says there..."let us make man..." he could have been saying, make the first living man and call him Adam, or let's make mankind in our image or make a specific species (homosapeins?) in our image. I'm not sure which I lean towards in belief.

Things we do know from the scripture.....Cain was afraid that someone would kill him when he was thrown out of the Garden. He was afraid right then, not at some future point years away that a sibling or cousin might kill him. And Cain married someone, and it wasn't his sister, since he didn't have a sister at that time.

The obvious conclusion is that there was some other kind of being, humanoid living on Earth at the same time as Adam and his family. I think it was the Neanderthals.