Source: BBC

When William Erasmus Darwin was born in December 1839, his father Charles began to meticulously record observations of his firstborn in a notebook.

Now housed at Cambridge University Library, it reads more like a research document than like that of a new parent blissfully observing his son’s behaviour, as the opening comments reveal:

“During first week, yawned, streatched [sic] himself just like old person – chiefly upper extremities – hiccupped – sneezes sucked….”

Today we know a good deal about Darwin’s theories. We know far less about how his private life – particularly his family – contributed to his work. But his vast collection of letters and the notebook reveal an intriguing side to the founding father of evolution: Darwin as a family man.

What’s more, his children’s development helped inform his understanding of human evolution.

Darwin’s son William was born a year after the scientist first met London Zoo’s first orangutan, Jenny.

“The orangutan for Darwin was like a window into the origins of mankind,” says John van Wyhe of the National University of Singapore and director of Darwin Online, which hosts a collection of all of Darwin’s published works.

Many parents make notes about their children but not quite like this

At this time, Darwin was already forming ideas about where humans came from, but he had never met one of our close ape relatives to test these theories. His encounter with Jenny helped cement his idea that that we share a common ancestor with apes.

He was already looking for a “real relationship between humans and apes”, says van Wyhe. When he saw Jenny’s facial expressions and noticed her social behaviour, it reaffirmed his ideas.

Babies and orangutans share many traits (Credit: Trinity Mirror/Mirrorpix/Alamy)

What stood out to him was how human-like some of her behaviour was, which he wrote about in a letter to his sisterSusan:

“The keeper showed her an apple, but would not give it her, whereupon she threw herself on her back, kicked & cried, precisely like a naughty child.”

When his son was born soon after, it meant that he could see first-hand how a human child developed, and consider the relationship between humans and animals. At times, he even referred to his son as “it”.

I made loud snoring noise, near his face, which made him look grave & afraid & then suddenly burst out crying

Many parents make notes about their children but not quite like this, says Alison Pearn, a historian at Cambridge University Library who has spent more than 20 years analysing thousands of Darwin’s letters. “This is very much a set of research notes.”

The notebook provides an intimate glimpse of Darwin as a good-humoured though curious father who is “prodding and poking his young infant like he’s another ape,” says van Wyhe.

His initial observations about both his family and Jenny the ape went on to influence his 1871 book The Descent of Man andThe Expression of the Emotions in Man and Animals, published in 1872.

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