I just stumbled onto two amusing articles, Ancient legends once walked among early humans?, and The discovery of material evidence of a distinct hominin lineage in Central Asia as recently as 30,000 years ago is no surprise. The second is a letter from a folklorist:
Sir, The discovery of material evidence of a distinct hominin lineage in Central Asia as recently as 30,000 years ago (report, Mar 25) does not come as a surprise to those who have looked at the historical and anecdotal evidence of “wild people” inhabiting the region. The evidence stretches from Herodotus to the present day. The Russian historian Boris Porshnev suggested that they are relict Neanderthals, although the lack of evidence of material culture suggests a type closer to Home erectus.
Needless to say many are skeptical of folk memories persisting for 30,000 years, though a standard assumption in paleontology is that the earliest and last fossil find of any given species is going to underestimate their period of origin and overestimate the period of extinction. In other words the Denisova hominin lineage almost certainly persisted more recently than 41,000 years ago. But recently enough to spawn legends of Enkidu? I'm skeptical. Someone with a better grasp of the mutation rate in oral history can clarify, but it seems that tall tales would be so distorted over a few thousand years that the initial kernel of truth would quickly be obscured. Here's my model for why almost all cultures have tales of various semi-human groups: cross-cultural differences are stark enough that it isn't too hard to dehumanize other populations. More specifically, I think the biggest gap is going to be between groups who practice different modes of production. Many of the "wild people" as perceived by agriculturalists were probably just marginalized hunter-gatherers who hadn't taken up the ways of "humans." Consider how many upper middle class white Americans perceive rural people from Appalachia even in our enlightened age. There are even biological differences, as agricultural populations seem smaller and more gracile in comparison to hunter-gatherers (who consume more fibrous food stuffs, and probably have a more balanced nutritional intake). How hard is to conceive of a small and malnourished agriculturalist being cowed by more robust hunter-gatherer group upon first contact?* Combine real cultural and biological differences with human imagination, and it seems that this is the most likely explanation for the universality of wild people and strange semi-human folk. It is in other words simply an aspect of evoked culture, nothing that needs special triggers in the form of other human lineages. The main exception I can think of would be Flores Hobbits, who may have persisted down to a very recent period. * The immediate objection to this possibility is that hunter-gatherer groups tend to get sick very quickly with the approach of high density humanity, and already pushed to less productive land by the time they're confronting the agriculturists on a daily basis. So they are less likely to be robust.