Imagine going to dinner with Charles and Emma Darwin and, the minute you get through the door, being dragged off by the famous scientist to take part in one of his experiments. That is exactly what happened to a series of visitors between March and November 1868 when Darwin was researching for his book The Expression of the Emotions in Man and Animals; the experiment has now been recreated online combining 21st century techniques with Darwin's own test materials as part of research by the Darwin Correspondence Project on 'Darwin and Human Nature'. You can take part at www.darwinproject.ac.uk/emotions/
We can get a very good idea of what was going on from surviving letters and manuscripts - it's an exciting, and perhaps surprising, close-up view of Darwin at work surrounded by family, friends, and colleagues, all of whom get involved. One visitor described what happened: "Mr. Darwin brought in some photographs taken by a Frenchman, galvanizing certain muscles in an old man's face, to see if we read aright the expression that putting such muscles in play should produce"- the guests admitted that they'd all gone off afterwards and made faces at themselves in the mirror.
The photographs were from a book by the physiologist, Benjamin Duchenne, whose claim to be able artificially to simulate convincing expressions using electrodes Darwin wanted to test. The eleven black and white photos he used - and that we reuse in the online test - have a bit of a ghoulish quality. Both Duchenne and Darwin were keen to stress that the people in them weren't in pain - well, OK, not much - but when Darwin later reproduced some of them in Expression he had two engraved with the electric probes left out - a nineteenth-century version of photoshopping.
Darwin was investigating the claim that our ability to express emotion is evidence of our separate creation; he argued that most human expression is innate, with shared expressions being evidence of the common descent not just of all human races, but of humans and other animals. This experiment, part of his wider research programme, was not a scientific experiment as we understand it today: there was no control group, the experimental materials were not consistent across the whole trial, and he used a very small number of test subjects by modern standards, but this was pioneering work in a field where methodology is still a thorny issue.
We hope recreating his experiment will get people thinking about some important and intriguing questions: Are there core emotions? What are they and how many? Why do we express emotion in the way we do? How do we recognise it and can we be sure we all mean the same things? Is the expression of emotion innate? Or is it culturally modified? How do we equate different words to describe emotion? Can a static image ever convey emotion accurately?
Darwin claimed that he had not led his witnesses, but that the photographs had been tested by "showing them to many persons without any explanation and asking what they meant". This would be described today as a "single-blind" test, Darwin's tables of results - which you can also see on the website - show that actually he was refining his method as he went.
The tables aren't dated, but we worked out their order by matching the sequence of visitors with references in letters and diaries. The first batch of visitors saw only seven of the eventual set of eleven photographs, and the first few responses consisted of "yes/no" answers, suggesting that, rather than asking what the expression was, Darwin had asked simply whether the photographs showed what they were supposed to.
We showed the tables and the original photographs to two other Cambridge groups whose work builds on what Darwin started - one at the Computer Lab teaching robots to recognise human expressions, and the other at the Autism Research Group, where Professor Simon Baron-Cohen and his team use brain imaging in studying recognition of emotions. Darwin's tables are roughly drawn on rather scrappy bits of paper - pioneering science in a field that now uses MRI scans and supercomputers started with nothing more than basic materials and a sharp mind. The three groups have begun a collaboration, launched this Saturday at Cambridge University's Festival of Ideas - the UK's only festival covering the arts, humanities and social sciences. The 21st century Darwin experiment uses a format developed by the Computer Lab and shows Darwin's photographs alongside some of the video clips of the Emotions Library developed by the ARC.
We don't know what Darwin's selection criteria were for his test subjects, or even if they were volunteers, or conscripts. In the middle of conducting his experiment Darwin went off for a family holiday to the Isle of Wight where he was introduced to the poets Tennyson and Longfellow - its a pity he didn't ask them what they thought.