Using experiments in which people were asked to read text, look at pictures, and hear words, short passages of music, sentences, and nonsense syllables, then asked between minutes or days later what they remembered, (using binary yes-or-no answers, some of which could be answered merely based on vague recollections) then comparing those answers to that of a control group, Bell Labs scientist Thomas K. Landauer (pictured above) determined in 1984 that human beings can retain about 2 bits of memory per second. This holds under all experimental conditions whether the information is visual, verbal, musical, etc. You can read more on this at “How Many Bytes in Human Memory?” by Ralph Merkle.

Over the course of a species-averaged 30-year lifespan, with 15 waking hours per day, this rounds to about 150MB of memory per lifetime. That means that a 30-year old human would be able to make approximately 1,200,000,000 binary distinctions based on memories until their ability to make distinctions based on memory reaches breaking point. Consider that a typical courtroom hearing probably extracts no more than a few thousand bits (perhaps a KB at most) from witnesses based on testimony. Using that as a reference, this number seems reasonable, if not a bit high. The estimate also assumes that people are exposed to novel information content every second of their waking lives.

Of course, some prodigies, such as Daniel Tammet, probably are capable of retaining significantly more information than 2 bits per second, but this is a unusual case.

Given that approximately 107 billion people have ever lived on this planet (”people” meaning members of the species Homo sapiens since 50,000 BC), we can derive a rough estimate of the total information content of our species’ entire memory, present and past:

1.07 x 1011 x 1.5 x 108 bytes = 1.6 x 1019 bytes.

This works out to approximately 107 terabytes, around 20 times the information generated by the entire Internet in 2002. Another way of putting it is approximately 16 exabytes. According to Roy Williams of Caltech, all the words ever spoken by human beings sum to about 5 exabytes. So the adage that we pay attention and remember less than half of what other people say apparently holds true.

According to The Social Life of Information, and the prior linked source, the world generated 2-3 exabytes of unique information in 1999, and the number is increasing. Given that the memory capacity of present-day humanity is about 31 petabytes, (31 thousandths of an exabyte), we certainly rely on artificial storage media to record whatever information we want to archive.

The beauty of electronic storage is that we can generate as much information as we want, certain that we can always build new hard drives to store it as long as it is digitized. Without electronic storage, we’d only be able to remember about a hundreth of all novel information generated in a given modern year.