Yep ...quite possibly the density per square metre of cave dwelling or tribal/early city life might have been higher ....but these dense clusters were tiny and separated from the next (and probably mutually antagonistc) one by large amounts of hard and slow to travel distance....such an infection would be catastrophic to the tribe/group but self extinguishing globally ..... and by doing so join the list of evolutionary dead-ends.....fast forward to a cave/village of 12M people with constant speedy travel between it and all others like it globally and we're in completely different territory from traditional plagues.

Darwinistic evolution is reactive not proactive ...ie,a virus that killed all the tribe and couldn't jump to the next died out....all too late for the tribe .... Through what to our ancestors would seem like instant travel we've made the world one tribe .... VirusX might die out after a profligate destruction of our 'village' ......chalk one up to Darwin ...cold comfort for us though.

And don't get me started on the appallingly fragile nature of modern society and just how little damage could cause a catastrophic failure.

Chin-up ...we'll be fine smile

K