The probable bases for such portrayals could be that we are said to have evolved over time, some may refer to this as evolution. So during prehistoric times we are said to have been less civilised, and more wilder, hunting, and more able, or equipped in our nature to fight anything that may try to attack us. This is before houses, and even tents, so we basically lived in nature. Story continues. If this scene was during prehistoric times, this is before the invention of all kinds of weaponry such as guns and even knives we are used to seeing and using today. During this time we used spears, and this weapon was capable and made to fight the wildest beast, or any animal or enemy that may try to attack us for any reason. So in analysis this scene that is often portrayed depicts human kind in a era of time before we had evolved into the technological and more safe, less dangerous and more easy way of life We live now. :)
