
A recent paper, On Universality in Human Correspondence Activity, published in the journal Science by Northwestern University researchers, examined the letter correspondence of 16 famous writers, performers, politicians and scientists, including Einstein, Darwin, Sigmund Freud, Karl Marx, and Ernest Hemingway, and found that the 16 individuals sent letters randomly following a circadian cycle.
“No matter what their profession, all the letter writers behaved the same way. They adhered to a circadian cycle; they tended to write a number of letters at one sitting, which is more efficient; and when they wrote had more to do with chance and circumstances than a rational approach of writing the most important letter first.”
Even though the study’s original intent was to compare if modern e-mail response follows the same rhythm as hand-written correspondence; (the study proved that both methods follow the same cycles and rhythms), what’s even more interesting to note is, Luís Amaral’s (professor of chemical and biological engineering at the McCormick School of Engineering and Applied Science) observation that:
People are not that rational.
Circadian Rhythms
Accounts of circadian rhythm date back as far as the 4th century BC, when Androsthenes, a ship captain serving under Alexander the Great observed the tamarind tree’s diurnal leaf movements. These cycles were initially researched in 1729 by Jean Jacques Ortous de Mairan and later even by Darwin (one of the subjects of the Northwestern University study) in The Power of Movement in Plants.
Circadian rhythms are simply patterns of physical, mental, and behavioral changes that follow a 24 hour cycle. This cycle is regulated by the “master biological clock” in our hypothalamus where a group of 20,000 nerve cells are located.

The image below is an example of a circadian cycle, though according to the study of Chronobiology there are quite a few variations of these cycles.

Our modern consensus reality places rationality in such high regard, it is refreshing to find that our biological behavior is anything but rational.
“...a rose is not necessarily and unqualifiedly a rose... it is a very different biochemical system at noon and at midnight.” Colin Pittendrigh, 1965
In New York City: Albert Einstein Collection, 1700s-1998: This collection contains letters and notes by Albert Einstein, as well as photographs, clippings, items commemorating Einstein, the Einstein family tree, and autographs. The collection also includes a guest book from 1929 from Einstein's house in Caputh with entries made by guests who visited the house.
Leo Baeck Institute
Center for Jewish History
15 West 16th Street
New York, NY 10011
Resources:
On Universality in Human Correspondence Activity
Biological Clocks — Garden Variety Experiments
Rhythms of Life: The Biological Clocks that Control the Daily Lives of Every Living Thing
Photo credit: Overview of biological circadian clock in humans Wikimedia Commons
National Institute of General Medical Sciences
Other interesting articles:
Carl Jung's legendary Red Book at the Rubin Museum of Art in NYC
Scientific study reveals the handwriting of a liar
Beyond a high IQ: Emotional, social and ecological intelligence in NYC (VIDEO)