Neanderthals also, cousins not ancestors, have a modern sized brain. Evolution has thus become synonymous with progress, and the evolutionary process is seen as a ladder, with man on the top rung. No wonder that they saw, with such confidence, man as the pinnacle of evolution and progress moving ever onwards. And perhaps there was another reason. But the ladder, of course is false.
Life is more like a tree, continually branching, continually pruned by extinction.
If we want it to be a ladder, and often we badly do, then we have to choose a pretty diseased tree with only one twig still alive. Then that surviving twig becomes the epitome and we can produce a ladder quite easily by raking through the dead branches in the undergrowth. As an example consider horses. It's a fairly uncomplicated tree with a few live branches. You couldn't possibly do this for our modern success stories, the bats, the rodents, the antelopes and other cloven hoofed animals whose ancestors produce three impenetrable thickets.