What makes the population of early humans grow

The growth of their brains along with finding and creating better resources for themselves and their groups. Such as the Neanderthals using a special sap from a tree to keep fires lit for a longer period of time.

Social darwinism refers to the the theory that people who succeed in our economic system will one day out compete those who fail. one day the rich will out succeed the poor so we'll that there will eventually be no more poor