Carl Sagan

The units of biological evolution are genes. The units of cultural evolution are ideas.


Carl Sagan's Cosmos: 11. The Persistence of Memory

Extending the brain

Tens of thousands of years ago we reached a point when we needed to know more than could be stored in our brains.

We were forced to invent ways of storing information outside of our body:

  • Carving in stones and bones
  • Painting on bamboo and silk
  • Scratching onto wax

We have come a long way since then. In the last millennia we advanced to printing books and storing information digitally.


The paper revolution

For a long time all writings were done in single copies, on materials such as bones, stones, leather, bamboo and silk.

It was in China, between the 2nd and 6th centuries, that paper, ink and printing were invented, thus permitting many copies of a work to be made and distributed.


Europeans catch up

It took 1000 more years for the Chinese inventions to reach and catch on in Europe.

Together with the invention of movable type printing, they enabled Europe to grow its body of written knowledge significantly. Between 1450-1500 Europe advanced from a few tens of thousands of hand written books to 10 million printed books.

Learning became available to anyone who could read.



All written knowledge was made accessible through libraries.

Over time libraries expanded to store more and more information. From the Library of Alexandria that had 1 million papyrus scrolls to the New York Public Library that has 10 million books.

If you read 1 book per week for your entire life, at the end you'll have read a few thousand books. That's less than 0.1% of what's available in a modern library. The trick is to know which books to read.


The magic of books
  • Books take us inside the minds of other people
  • Books enable us to travel through time and tap the wisdom of our ancestors
  • Books bind together people that never knew each other


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