Liz Wetton travelled to the University of Cambridge's Museum of Zoology a few weeks ago expecting to spend her volunteering session in exactly the same way as she had for the past 10 years: sorting through the extensive collection of birds' eggs and rehousing them in new boxes.
On this particular day, during her routine egg sorting, however, the octogenarian noticed a tiny, chocolate-brown specimen with "C. Darwin" etched on it in faded ink. Assuming it belonged to the famous naturalist, Ms Wetton noted and boxed it as normal, assuming the museum must be aware of its existence.
Only when Mathew Lowe, the museum's collections manager, reviewed her work a few weeks later did she learn the significance of her discovery. Not only was the egg one of only 16 collected by Charles Darwin during his five-year voyage on the HMS Beagle in the 1830s, but it was also the only one to have since been found.