Category Archives: Blog Posts

The Great Explainers – Carl Sagan


My first proper blog post.  Whilst perhaps later, I’ll get my blogging shoes dirty with something substantial, for the moment I’m going to keep this fairly light.

Mark Esner, Adam Boxer, Ben Newmark and HistoryLover have recently written on “The Great Explainers” a series of blog posts on what makes a good explainer and explanation.  They have stimulated me to finally get started and blog on my favourite explainer, Carl Sagan, and what makes his explanations so perfect and so memorable.

Sagan* embodies many of the features that have been mentioned by others in this series of blog posts.  His explanations are delivered with the confidence of an expert, for indeed he is; his qualifications, accolades and day-job leave you with no reason to question his authority on any matter. He delivers his explanations with a precise language, his words carefully chosen to be rich and interesting, and yet clear and precise. He takes time to build his explanation carefully in easy to understand steps.

But what Sagan adds to his explanations, is an emotion, warmth and humanity. He does this by telling the human stories of discoveries. A classic example is his telling of the story of Eratosthenes, an ancient Egyptian polymath who read in the library of Alexandria of a site in Syene where columns cast no shadow at midday on the longest day of the year, how intrigued by this (since at the same time in Alexandria, columns still cast a shadow), he paid a man to pace out the 800 km to Syene and then used some simple Pythagorean geometry to calculate the curvature of the earth between Alexandria and Syene and therefore the circumference of the planet. Over 2000 years ago (take note Flat Earthers).


Sagan’s explanations are particularly memorable because of the extraneous human details of the story. We are, after all, evolved to remember human stories.

Primitive humans were at an evolutionary advantage if they could listen to, understand and remember a human story.  There was a benefit for our ancestors to listen to the survivor-story of a their fellow cave man; returned from a days foraging having narrowly avoided a wild animal attack.  By being able to recall the details of the story; the sounds of the bear and location of the attack as described by the surviving hominid, our ancestor avoided getting eaten by the hungry grizzly, whilst those who twiddled their thumbs and talked to the person sat next to them were doomed to be the next ursine meal. And thus, the genes for carefully listening to and remembering human stories were passed on and strengthened in humanity, and we became a species of story tellers, passing on our oral history from one generation to the next.

When I recall all my favourite lessons, lectures and demonstrations from my education, the most memorable ones always included details of the human stories behind the discovery.  For example, I vividly remember university lectures on the nerve action potential, which told the story of their discovery by Hodgkin and Huxley working on squid giant axons at the laboratory of the Marine Biology Association in Plymouth.  Their story was told to me, with the humanity included: their struggles to find a suitable nerve preparation in Cambridge that was large enough to take a micro-electrode; the pausing of their work for 8 years during the second world war; Huxley’s work on Radar and anti-aircraft guns during his war secondment; the destruction by a German bomb of their electrophysiological equipment in Plymouth; and most vividly of all the fact that post war, squid giant nerve axons that had generated good results would be “immortalised” by being thrown violently up, over their shoulder to stick to the ceiling, a practice that was continued by subsequent electrophysiologists working in the same laboratory.  Not only did I never forget the accompanying explanations of the nature of action potentials, but so fascinated by the story was I that I spent the next 10 years studying electrophysiology and would name my son after one of those great men.  Indeed, I got to see for myself the spagetti-like ceiling pattern of dried cephalopod nerves, still preserved in situ, when I visited the Plymouth laboratory during my PhD in 2002.

Hodgkin Huxley

Huxley and Hodgkin with their electrophysiological equipment.  From the cover of the Nobel Prize Programme Cover in 1963.

There are some that might argue that these details of the human experience are unnecessary and clutter the explanation of the required detail. But I would argue that the human stories are what make our brains sit up, tune in and take notice of the details. They are the hat stands on which we hang the rain coats and umbrellas of knowledge.  Without the human stories our minds are left to sort through the jumble pile of wet coats, often getting bored and giving up.

In almost any online video of Sagan you care to find, he always finds the human element to his explanations. His explanation of 4-dimensional tesseracts begins by asking us to imagine we are 2-dimensional beings living in flat land.  Or his answer to a young girl’s question “Is the sun part of the milky way galaxy?”

You are part of the milky way galaxy”. He tells her, the look on her face tells you she wont forget the answer.

So natural and brilliant is Sagan’s ability to tell a human story that he wrote a fantastic science-fiction novel that is scientifically plausible about the search for extra-terrestrial life in the stars, and what might happen if we were to find such a message. The book is Contact, and was made into a Hollywood blockbuster of the same name starring Jodie Foster.

In my opinion Sagan’s only peer in the ability to find the humane and emotional in any dry discovery or explanation is Bill Bryson who similarly tells so many human stories in his incredible Short History of Nearly Everything that the book is neither short, nor put-downable. It is the only book I can honestly say I’ve read completely from cover to cover more than twice**.  Yet while Bryson might own a roll-neck sweater or two, he doesn’t have that luxurious, imitable voice.

Whilst I don’t try to imitate his voice (often) in my own teaching, I do try to find the human stories to accompany the scientific knowledge I am imparting each lesson.  It’s why I love reading lay science books about scientific discoveries which I can then pass on to my students in the oral tradition. I find it gives everyone somewhere to hang their hats.




*my awestruck, reverence means I can never quite bring myself to call him by the familiar, Carl

** if you exclude the favourite bedtime books of Huxley and I.