There are many undiscovered mystery's and the majority of human history has long been forgotten. For the most part we can only speculate upon explanations as to why groups of early humanoids would be able to inhabit remote islands only to vanish thousands of years before modern homo sapiens staked their on claim to the entire planet.
There would no doubt have been circumstances in hominid evolution where isolated groups would become so utterly inbred that it was a threat to viability and in many of these cases this would lead to total collapse. Perhaps there may have been a combination of factors...such as after many years living in an isolated island paradise without outside predators and many generations of inbreeding, such island populations would lose their survivalist edge, so that they would be easily wiped out from any number of abrupt shifts in the climate...such as in the biblical flood or a volcano induced nuclear winter.....or else the ones who did survive the Apocalypse made their escape back to the mainland to chase after some terrestrial tail and merge back into the mainstream...
Think of human migration and miscegenation as a tidal phenomenon, forever ebbing and flowing like water, reaching out to the furthest frontier only to be pulled back by natural forces until the time is ripe to continue forward. The first waves of intrepid travelers laid the ground work for hominid adaptation to the most extreme climates on this earth, the genetic matrix fractured into many variations... some flowed to the ends of the earth, separating entirely from the connection to original source...while others ebbed back, called back in the direction of origin. These intermediaries merged with the following waves of groups that left the cradle much later.
These interbreeding between subsequent migration waves of constantly mutating strains of humanoids, allowed for the transference of valuable adaptations which took millennia to accrue....from the first wave to the second wave, and from the second wave on down the line...the aggregation and coalescence of traits developed on the edge of the frontier, through incessant migration and interbreeding, finds its way from the very brink of separation back to the core....the infusion of cutting edge frontier DNA further seduces the core to leave cradle phase as it radiates its own eminence into further lands.....of course there was never a linear progression and these evolutionary migratory waves occurred on multiple dimensional levels and scales, but for the sake of explanation certain reduction-isms are permitted.
These waves of forward flowing migration patterns, followed by the ebbing of progress, leads to countless reversals of course, bringing the once separate strains of human beings into a concrescence of miscegenation. This allows for a piggybacking effect by which the following waves that left the cradled much later, when interbred with the forerunners already epi-gene-mutated to thrive in the frontier territory, are more quick to adapt and find balance, as each next newfangled wave pushes the evolutionary envelope further than the last.
This ebb and flow of the evolutionary migration patterns of human kind, is reflected through all the evolutionary patterns and movements of life on this planet. The origin of the "first" wave is so far back into the dark infinite abyss of time, that one could only imagine....The origin of animal life could be traced back to first acts self determination in the early seething slime mold and flagella wielding bacteria able to move with purpose in the direction of destiny..... Likely on some fractal level, these evolutionary patterns responsible for the creation and development of life are related to the flow of the light, energy, and spirit that created the entire cosmos.
