After a meteoric rise, through youth and early adulthood, they begin to settle down before dropping back gracefully to a comfortable old age.

Almost no one, including sophisticated economists and financiers, realized that the steep increase in housing prices that ended in 2006 was a bubble phenomenon.

He turned abruptly and walked back the way we'd come.

The most surprising revelation from this chart is the steep incline seen in the age group 12-24. Over the past few months, this group's participation levels have been increasing dramatically.

Others give an indication of people's interests or emotions, with an annual spike in searches for anti-depression drugs around Thanksgiving time in the United States.