For a scientist who spent much of his career capturing and killing animals for his collections, you may assume Charles Darwin had few scruples when it came to how they died.

But new documents which are coming up for sale at Sotheby’s later this month show Darwin was a kind-hearted animal rights activist who campaigned for the abolition of steel traps.

In the 19th century it was common for gamekeepers to use traps to keep vermin under control, but they could be lethal for larger animals like dogs, foxes and deer which became ensnared.

In the notes from 1863, which have remained with his descendents until now, Darwin sets out his concerns and appeals for the use of humane deadfall traps, which kill the animal instantly rather than leaving them to suffer.

In the same year, Darwin and his wife Emma published a four-page pamphlet on the cruelty of steel traps, which generated such a response that they were able to raise funds and persuade the RSPCA to launch a competition to design something less barbaric.