For eons, all manner of animals have lived their lives according to the cycles of the Earth’s rotation on its axis, the moon’s orbit around the Earth, and the Earth’s orbit around the sun. But why do we observe the week? The pattern of living on a seven-day cycle—with one or two of those days set aside for rest—is a relative novelty. Only in the past few centuries, with Western colonization of most of the world, have the majority of human societies adopted it.
The case for the week was never airtight. It’s now weak and getting weaker. Most Westerners no longer observe a weekly Sabbath, and the coordination advantages of keeping everyone on the same uniform schedule have evaporated. So why does this arbitrary time cycle still dictate the rhythm of our lives? Is it time to abolish the week and find a better way to structure time?
The rationale for the day is as clear as, well, day. In a 24-hour period, most points on Earth experience a full cycle of light and darkness. It makes sense that humans and other organisms have evolved to adjust their patterns of behavior according to those daily patterns of light and heat.
Many organisms have also adapted to the annual environmental changes wrought by the Earth’s orbit around the sun. Countless animals migrate, hibernate, or breed on a yearly schedule. Humans have likewise long organized their lives around the annual fluctuations we call seasons.
The environmental influence of the lunar cycle is subtler, but no less real. It affects the tides and the amount of light available at night. While many animals have adapted their biology to the phases of the moon, it remains controversial whether humans have done so. (Despite its name, for example, we still don’t know for sure whether the female menstrual cycle evolved to be in sync with the lunar cycle).
But whence the week? Throughout history, human societies have found it useful to divide time into groups of days shorter than a lunar month. One of the most common uses of this cycle has been to establish a regular market day, though just how regular varies. At one point, the Basques evidently employed a three-day week. For centuries, China, Japan, and Korea employed a 10-day week. Other societies have employed four-, five-, six-, eight-, and nine-day weeks.
So how did lucky No. 7 come to rule our calendars? It all began logically enough, when the ancient Babylonians divided their lunar months into four, yielding weeks that were mostly seven days. Then superstition kicked in. The final day of the week came to be considered evil or unlucky, and certain taboos developed around that day—against eating meat, for example.
It’s likely that the Babylonian week was the model for the seven-day Jewish week, with its own taboos against certain behaviors on the seventh day, or Sabbath. Babylon also probably served as the source of another important seven-day week used in Hellenistic Alexandria. The influence of that week remains with us in the names of heavenly bodies it assigned to each day—like Saturn-day, Sun-day, and Moon-day.
Meanwhile, the Romans marked time differently, which is why you never heard of anyone warning Caesar to “beware the third Tuesday in March!” Roman lunar months began on the Kalends, which scholars believe coincided with the new moon. The Ides, which fell on the 13th or 15th day of a month, coincided with the full moon. The Romans also kept an eight-day market week.
As Christianity—which kept the Jewish week but moved the Sabbath to Sunday—and Egyptian astrology gained influence in the empire, so did the seven-day week. Constantine, the first Christian emperor, made it official in 321. Since then, the spread of Christianity’s influence—as well as that of Islam, which also employs a seven-day week—has imposed the seven-day cycle on most of the world.
But there’s nothing inevitable about the ceaseless repetition of six days of work, one day of rest. As labor has become both more productive and more organized, the week has evolved. The writer Witold Rybczynski traces the emergence of the weekend to 19th century England, when the British agricultural revolution made land and labor more productive. At first, Rybczynski relates, this allowed workers extra leisure, which they enjoyed spontaneously—not according to any ironclad schedule. As the Industrial Revolution became a driving force in trans-Atlantic civilization, the push for greater efficiency demanded standardization of this extra leisure. In 1926, Henry Ford began shutting his factories on Saturdays in a bid to crystallize an American convention of a two-day weekend full of recreation (that he hoped would involve driving). It worked.