They planned ahead, Erasmus thinking "It will be very pleasant our being together, we shall be as cozy as possible", arriving early at Edinburgh to make social contact with old friends of the family in Whig society, and so "we can both read like horses".

In the summer of 1829, he gave up medicine as his father Doctor Robert Waring Darwin considered that Erasmus's "delicate frame" could not withstand a career "involving, if successful, a severe strain on body & mind" and decided to pension him off.

Eras was "very agreeable" to retiring at the age of 26 and planned to live in London with "an air cushion in his rooms" to allow a visiting Charles to stay with him.

In May 1834 Charles got a letter from his sisters recommending Poor Laws and Paupers Illustrated in pamphlet-sized parts by the fiercely independent literary Whig Harriet Martineau, and telling him that "Erasmus knows her & is a very great admirer & everybody reads her little books & if you have a dull hour you can, and then throw them overboard, that they may not take up your precious room".

[5] In October 1836 after Charles returned from the voyage he stayed with his brother in a bustling London, where Erasmus enjoyed a life of literary leisure, his week revolving around intellectual dinner parties, spending his days with Miss Martineau.

He begins to perceive, (to use his own expression) he shall be not much better than her 'nigger'.— Imagine poor Erasmus a nigger to so philosophical & energetic a lady.— How pale & woe begone he will look.— She already takes him to task about his idleness— She is going some day to explain to him her notions about marriage— Perfect equality of rights is part of her doctrine.

"[7] In December Charles called on Martineau and remarked that "She was very agreeable and managed to talk on a most wonderful number of subjects, considering the limited time.

In April 1838 Charles told his older sister Susan that he had seen the rhinoceros in the zoo let out for the first time that spring, "kicking & rearing" and galloping for joy.

In the summer of that year Martineau's health broke down during a visit to the Continent and, fearing a tumour she retired to solitary lodgings in Tynemouth near her brother.

While Charles Darwin's illness made him increasingly reclusive after his move to Downe, he would still visit Erasmus as one of his relatives and friends who provided safe havens.

As the reaction to Darwin's theory began following the publication of On the Origin of Species at the end of 1859, Erasmus thought it "the most interesting book I have ever read", and sent a copy to his old flame Harriet Martineau who at 58 was still reviewing from her home in the Lake District.

Francis Galton, having caught the fad for Spiritualism, arranged a séance in January 1874 at Erasmus's house with those attending including Charles, Hensleigh Wedgwood and Thomas Huxley.

Emma Darwin broke the news to Charles, who commented that he had seen Erasmus dying slowly "for many years", not "a happy man" but always kindhearted, clearheaded and affectionate.