This film dramatizes the concerns of 2 quite different prehistoric peoples, who come together in the end to form one culture. We might think of the Rock people as Neanderthals, and the more advanced Shell people as Cro-Magnons. However, if we take the date One million BC literally, modern humans had not yet evolved, and we are dealing with pre-human Hominoids.
Since they wear clothing, which evidence suggests is a much more recent invention, I will assume that we are dealing with much more recent human-like beings........ There are many anachronisms. The most glaring example is the inclusion of various reptiles and mammals made up and greatly magnified to resemble dinosaurs or other prehistoric beasts. Dinosaurs, of course, vanished 64 million years before humans emerged. Even more anachronistic is the inclusion of a sail-backed Dimetrodon, made by gluing fins on a crocodilian. Dimetrodon was not a dinosaur, per say. In fact, it belonged to a group that went extinct about 250 million years ago, before the first dinosaurs emerged! Dogs weren't domesticated until perhaps 20,000 years ago, and it is doubtful the early ones looked anything like a Great Dane......... We see the Shell people eating nice big juicy apples that weren't bred until comparatively recent times, from much smaller, sour, progenitors........The prologue consists of a group of rock climbers seeking shelter from a thunderstorm. in a sizable cave. They discover an archeologist, played by Conrad Nagel, examining an extensive set of wall paintings. To pass the time, he offers to tell them the story that the paintings suggest.........Seems there were 2 local bands of humanoids. The Rock people were more primitive in several ways. They lived on mountains, ate exclusively meat, practiced an extreme version of survival of the fittest, and wielded shafts without stone spearpoints . Without spears, I find it difficult to believe that they were fierce warriors and hunters, as suggested........... On the other hand, the Shell people had spears with stone spearpoints, yet were mostly vegetarians, subsisting on modern fruits and vegetables that didn't yet exist in the real world. Socially, they were more cooperative, treating the relatively week members with deference. Thus, in contrast to the Rocks, they allowed children and women first choice at the food stewing in the communal hole in the ground, that served as their cooking pot. Also, the sick and disabled were cared for. Apparently not warlike, presumably, they carried their spears as defense against the various large wild animals and waring tribes......... Apparently, Victor Mature, with only one minor film role under his belt, was judged to have the right physique and looks to carry the lead Tarzan-like role of Tumak, son of the leader of the headman of the Rocks. He was banished from the Rocks for fighting, surviving a push off a cliff, and fall into a swift stream. He floated downstream to the territory of the Shell people, where he was discovered, resting in a little cove, by the maiden Loana, played by Carole Landis. She soon decides he's the man for her, although being a foreigner. She teaches him the ways of the Shell people, such as being kind to the less fortunate, and the use of the spear. But, eventually, he is banished for stealing a spear. Loana follows him, as they head toward the Rock people. Surprisingly, Tumak soon establishes himself as the leader of the Rock people(perhaps partly by his possession of a spear?). He has several encounters with beasts, and watches several fights between beasts. Eventually, the nearby volcano explodes, sending lava down, to inundate the people's villages(I thought the Rock people lived high on a mountain?). Further terror is unleashed by the opening of huge cracks in the earth, as an earthquake accompanied the volcanic explosion(not unusual). One mother is consumed by the lava. Tumak and Loana adopt her small girl, who survived. Now, the Rock people are threatened by a huge dinosaur who has them trapped in a cave. The Shell people show up to try to defeat the monster. Their spears bounce off it's thick hide, so they succeed by causing a rockslide that plummets the beast to death. The two tribes join, as symbolized by Tumak and Loana walking into the sunset, with their adopted girl between. Interestingly, physical and molecular evidence suggests that the Neanderthals and modern humans interbred, to some degree.........This story was remade in 1966, with the voluptuous Rachel Welch, in a revealing bikini, serving as Loana. Not having seen it, I won't comment on other comparisons, except the obvious Technicolor vs. B&W photography.