maybe it wasn’t as chilly as we thought? If people used the equivalent of 16-brick stoves which use very little fuel, would there be fire traces of their use?
Actually, Sterno stoves were used. They were so valued, that they were passed down through the generations and is why we can not find any evidence of them in archeological digs.
http://www.sterno.com/retail/pages/stove.html
;^D