A 2001 study in Science magazine found that matriarchal African elephants are essential to the well-being of elephant social groups because they possess social memories that enable them to recognize if outsiders are friendly to the herd. “Elephants can certainly build up a memory over the years and hold on to it,” said the study’s lead author.

“There is one thing at which I cannot sufficiently wonder,” wrote Pliny the Elder, “that of some trees, the very memory has perished, and even the names recorded by authors have passed out of knowledge.”

According to film director Joe Swanberg, a significant number of people believe that an obscure 1985 film about mind control was not in fact real, and that they had dreamed the particulars of the Quebecois film. “The Peanut Butter Solution,” wrote Swanberg, “successfully convinced young viewers that they dreamed it rather than watched it.”

According to philosopher Alfred North Whitehead, “Writing was an invention which took about two thousand years to make its effect felt. Do you recall, even in Plato’s dialogues, the discussions are seldom if ever about what the participants have ‘read’ but almost invariably about what they ‘remember’?”

Researchers at the MIT Media Lab recently determined that all cultural products “follow a universal decay function.” People and things are kept alive through “oral communication” for about five to thirty years. “Biographies remain in our communicative memory the longest (twenty to thirty years),” according to their report, “and music the shortest (5.6 years).”

“Memory,” wrote the novelist Jean Paul in 1816, “is the only paradise out of which we cannot be driven away.” Critical theorist Theodor Adorno disagreed with his assertion. “Memories cannot be conserved in drawers and pigeonholes,” he wrote in response. “Precisely where they become controllable and objectified, where the subject believes himself entirely sure of them, memories fade like delicate wallpapers in bright sunlight.”

After the death of Muhammad in Medina in 632, the Quran was preserved by followers who memorized its contents. Those who can recite from memory its 78,000 words are known as hafiz or hafiza. There are said to be millions today who have completely memorized the holy text. In 2005 Amina Abdul-Majid, a blind sixteen-year-old Somali, became the first girl to win a Quran recitation competition held in Mogadishu.

Malingering amnesia, in which a person fakes symptoms of memory loss, is often associated with attempted financial gain, typically among personal-injury claimants. According to a 2003 study, 29 percent of criminals sentenced to life imprisonment claimed at their trials that they suffered from amnesia. A visual recognition test, such as the Test of Memory Malingering, can be used to detect fraud of this kind.

In 1956 psychologist George Miller published a paper that claimed the average number of objects a typical human can hold in short-term memory is seven (plus or minus two). “What about the magical number seven?” he wrote. “What about the seven wonders of the world, the seven seas, the seven deadly sins, the seven daughters of Atlas in the Pleiades, the seven ages of man, the seven levels of hell, the seven primary colors, the seven notes of the musical scale, and the seven days of the week?”

In 1995 cognitive psychologist Elizabeth Loftus conducted a study in which she presented to twenty-four people four stories about their childhoods. Three of the stories were true; one was false. Five of the twenty-four people falsely remembered the “lost in a mall” story. “People can be led to remember their past in different ways,” concluded Loftus, “and they even can be led to remember entire events that never actually happened to them.”

In 1927 Russian psychologist Bluma Zeigarnik identified a phenomenon that came to be known as the Zeigarnik effect, which states that waiters are good at remembering particulars of a restaurant bill—until the bill is paid. “Unfinished tasks are remembered approx­imately twice as well as completed ones,” concluded Zeigarnik.

Written in Los Angeles in 1955, the song “Memories Are Made of This” became a number-one hit for Dean Martin. It was a surprise success in Europe, spending four weeks at the top of the UK Singles Chart. A German version, performed by Freddy Quinn and recast as “Heimweh” (“Homesickness”), was the most popular German song of 1956. As “Honvágy-dal” (“The Song of Homesickness”) it became the anthem of the 1956 Hungarian Revolution.

The first written language, Sumerian cuneiform, is believed to date to around 3000 bc. Archaeologists have found evidence that astronomical texts were still being written in cuneiform in the first century of the Common Era; decadent varieties of the language survived to the time of Christ.

“When Simonides or someone offered to teach him the art of memory,” Cicero noted in his De Finibus, the Athenian politician Themistocles “replied that he would prefer the art of forgetting. ‘For I remember,’ said he, ‘even things I do not wish to remember, but I cannot forget things I wish to forget.’ ”

“Animals retain the memory of their experiences and have no need of mnemonic systems,” according to the third-century Roman writer Aelian. “A horse, on hearing the clash of curb chain and the clang of bit, and seeing chest plates and frontlets, begins to snort and makes his hoofs ring as he prances, and is in an ecstasy.”