No recorded history is available to trace the development of social behavior of humans but sociologists and archaeologists make suggestions that cover a wide range of possibilities. Current cartoons of early mankind favor the image of a brute dragging a woman by the hair into his cave. Now people visualize dirty savages hovering in fear of predators, fire, and storms.
Considering that those early peoples – and at first they must have been very few – had the capability to think, remember and plan. Years went by – perhaps decades – before the realization that after short days the sun would return. But that did not happen for the eons our ancestors lived in “Eden”. The solstices are not celebrated in the tropics. Why not?
In the tropics where humans likely evolved the days are almost equal in length to the nights. That is true now and would have been no different a few million years ago as long as the axis and rotation of the earth was as it is now. So the understanding that the sun changed the length of days was not relevant until clans or individuals went northward. The farther north humans went the more challenging the conditions they found. Probably even the weather in the Mediterranean area was not harsh enough to concern people about length of daylight hours. Clans gathered around safe ports and created villages fed by fishermen while the home-bound learned to plant and harvest on the hillsides. Some individuals observed and thought.
Farther north people shivered with the first cold winds that swept down from the arctic. They hunkered inside caves with fire for warmth and light. They processed hides for clothing and blankets, painted pictures on the walls, counted time until daylight lengthened and the sun once again welcomed them outdoors.
Solstices were celebrated when villagers found time on their hands and in their days. Time spent outdoors at work or leisure allowed more than one insightful individual to notice the annual positions of the sun. Each year those familiar positions were anticipated with relish, if for no other reason than to verify past observations. Excitement is as contagious as the measles so the next step is to be happy and dance and sing to celebrate a natural occurrence when it comes.