Scientists have discovered that male, human ears grow in seven-year cycles, reviving the ancient Greek belief that there are circaseptennial rhythms in human development.
The discovery follows the revelation last year that male human ears continue to grow throughout life - at about 0.22mm a year in men aged over 30 - supporting the observation that some very old men have big ears in relation to their skull size.
Dr Jos Verhulst of the Louis Bolk Institute in the The Netherlands and Patrick Onghena at Katholieke Universiteit Leuven in Belgium, analysed ear length values from the age of 30 to 83 and found that ear-growth velocity peaked around multiples of seven years.
They write in the British Medical Journal: "The idea of a seven-year rhythm in human development is old, dating back at least to ancient Greece. Reports on circaseptennial phenomena are, however, scarce in recent published work.
"Seven-year periodicity remains comparatively unknown, perhaps because it is not looked for by many researchers. This may be because no major seven-year rhythms seem to be present in the natural environment. In this respect, the circaseptennial rhythm differs from the better documented circadian and circaseptadian rhythms, which can be linked to day-night cycle, and to tidal periodicities, respectively."
Professor Ian Stewart, of the Mathematics Institute at Warwick University, says that in the Hippocratic tradition the number seven governs the ailments of the body. In Germany it was believed that people would not catch swine fever if they spent seven days drinking and bathing in water containing asphodel (a type of lily). A Jewish cure for fever involved taking "seven prickles from seven palm trees. seven chips from seven beams, seven nails from seven doors..." and so on, up to "seven hairs from the beard of an old dog".
Numerologists see seven as the sum of the spiritual three and the material four, signifying the creation. The world, according to the Old Testament, was created in seven days. Psalm 90 sets the human life span at seven decades; Solomon's temple had seven steps, and Noah's dove returned to the ark after seven days.