Humans more than likely instinctively knew which foods were safe the same way their genetic ancestors did. Since humans evolved alongside other similar species they would share similar instincts on what to look for in safe to eat vs not safe to eat foods.
On a serious note
Humans more than likely instinctively knew which foods were safe the same way their genetic ancestors did. Since humans evolved alongside other similar species they would share similar instincts on what to look for in safe to eat vs not safe to eat foods.