Another, more recent, theory suggests it may have to do with our inability to maintain a stable posture in a moving environment.

One theory suggests that big money flees to art as a safe haven in times of recession.

One theory suggests a single point of separation about 40,000 years ago.

But another theory suggests that the glaciers come from above, not below, as the atmosphere condenses into frost, forming thick ice sheets over time.

Its detractors say that it looks good on paper but in reality markets are rarely as efficient as the theory suggests.