BAD weather made our ancestors huddle together in defensive settlements, according to a study of climate variation and fort building in Ireland over the past 9000 years.
Chris Turney of the University of Wollongong in New South Wales, Australia and colleagues had charted climate changes in the North Atlantic region using Irish bog oaks (Â鶹´«Ã½, 11 October, p 11). This work revealed a clear wet/dry cycle with shifts about every 800 years.
But when they looked at the ages of Irish forts, crannogs (dwellings constructed on an artificial island in a lake or marsh) and settlements, they found…
