Man has a fascination with his early forms for good reason. Early Man was father to the child, and the child wishes to know whereof he sprang. Early Man's appearance changed as his developmental stages changed - ranging as one would expect from ape-like to man-like. Hypothesis on his appearance almost always leans in the direction of man-like traits, as humans feel uncomfortable to some degree when contemplating their origins. Monkeys have bright coloration on their faces and behinds, and so did early White Man. Sharp prominent teeth were a characteristic of Gypsy Man, whose grimacing face was more tooth than otherwise. African Black Man was covered with hair, in his early stages, and though black men of today are without beards in the main, beards were present in the prototype. And the descendants of China Man would be surprised to learn he had a tail for quite some time.
Man, in each of the 6 races, was developed in stages, and between these development stages was allowed a period of time for things to settle down and for the genetically engineered product to be road tested. Would it break down? Frequently this happened, resulting in intervention, fine tuning the product to correct whatever was deemed to be the problem. Archeologists discover bones, such as those of Neanderthal Man, and wonder what became of him. Did he die out? Did he evolve? It seems he rather abruptly disappeared, and such a strapping fellow, he was!
Neanderthal Man was taken in hand to correct a problem. All of him? Yes. This was affected by making him sterile, a simple snip to the male, where he roamed free, and genetically engineering those taken into the lab. So there be no misinterpretation, let us explain that the lab did not consist of cages, but in this instance was an island, and a paradise at that. The lab was a controlled environment, but with no more controls than necessary. So what were Neanderthal's problems, and what did he become? Neanderthal, big brute that he was, had a digestive problem. It is often assumed that he died out because he was stupid, or confrontational, but he was none of these and underwent change only because he had tummy troubles. He was not living his full life, and some died young, due to inability to digest the foods available, to take advantage of the fauna and flora that were perforce his menu. Coming out of his genetic correction, and returned to his environs, he looked different - a bit like Cro Magnon Man.
The bones of Homo Erectus simply mark the evolution of more than one race at a particular stage. Where did he go? Into the labs to become the next stage. You can equate the puzzle archeologists are trying to put together with litter along the highway. Here there are Coke bottles, there plastic wrappers, and at yet another stretch, no litter at all. If one did not understand that litter was influenced by recycling efforts and laws, the price paid for aluminum and glass, and the dedication of local groups or commandeered prisoners set out to pick the roadside clear, the patterns would make no sense. The missing link in the evolution of man is not a particular pile of bones as yet undiscovered, it is the teams of genetic engineers who periodically descended on Earth to check on their handiwork, and left when mankind had made another leap.