The emotion in the film apparently comes from Darwin telling the story of the orangutan Jenny, who dies of pneumonia in the arms of her keeper, to his beloved daughter Annie.

There is some historical truth to the story of Darwin and Jenny. Carl Zimmer talks about that in his introduction to Darwin's work:

"In the similarities between orangutans and humans Darwin saw signs of kinship, of a shared ancestry. On March 28, 1838, Darwin rode to the London zoo and paid a visit to Jenny, who was weathering the British climate in the heated giraffe house. As a wealthy guest, Darwin was allowed to enter the cage itself. In a letter he wrote four days later ... he described what he saw: '...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. She then looked very sulky & after two or three fits of pashion, the keeper said, "Jenny if you will stop bawling & be a good girl, I will give you the apple.She certainly understood every word of this, &, though like a child, she had great work to stop whining, she at last succeeded, & then got the apple, with which she jumped into an arm chair & began eating it, with the most contented countenance imaginable.'

Darwin watched Jenny gaze at herself in a mirror. She used bits of straw like tools. Her face contorted much as a child would. Others might believe they were vastly different from an orangutan, but Darwin didn't. He decided that much of that difference was a superficial matter of clothes and manners. His mind raced back to the people he had encountered on his voyage aboard the Beagle...

'Let man visit Ourang-outang in domestication,' he wrote in his notebook, 'hear expressive whine, see its intelligence when spoken [to]; as if it understand every word said, see its affection. to those it knew, see its passion & rage, sulkiness, & very actions of despair; let him look at [a] savage, roasting his parent, naked, artless, not improving yet improvable & let him dare to boast of his proud preeminence."

Darwin kept his notebooks secret. His dangerous thoughts about human origins would stew in his mind for over three decades. He would finally share them with the world 33 years later, with the publication of his 1871 book, The Descent of Man, and Selection in Relation to Sex.

http://www.carlzimmer.com/books/descentofman/excerpt.html