Charles Darwin (February 12, 1809–April 19, 1882) may be best-remembered as the father of evolution, but he was also a man of great dimension and extraordinary capacity for reflection. In his prolific correspondence, he contemplated everything from the pros and cons of marriage to the downturns of mental health. But having married the love of his life and fathered ten children with her, he also frequently pondered questions of fatherhood and family as a backdrop for his broader meditations on love, work, and happiness.

After weighing the benefits of marriage above its costs, Darwin confides in his bride-to-be, Emma, a few days before their wedding in early 1839:

I was thinking this morning how on earth it came, that I, who am fond of talking & am scarcely ever out of spirits, should so entirely rest my notions of happiness on quietness & a good deal of solitude; but I believe the explanation is very simple, & I mention it, because it will give you hopes, that I shall gradually grow less of a brute, — it is that during the five years of my voyage (& indeed I may add these two last) which from the active manner in which they have been passed, may be said to be the commencement of my real life, the whole of my pleasure was derived, from what passed in my mind, whilst admiring views by myself, travelling across the wild desserts or glorious forests, or pacing the deck of the poor little Beagle at night. — Excuse this much egotism, — I give it you, because, I think you will humanize me, & soon teach me there is greater happiness, than building theories, & accumulating facts in silence & solitude. My own dearest Emma, I earnestly pray, you may never regret the great, & I will add very good, deed, you are to perform on the Tuesday: my own dear future wife, God bless you.

Darwin intuited the “humanizing” capacities of a stable family early on — he was himself the product of loving parenting. In a March 1826 letter, his father writes to 15-year-old Charles:

It made me feel quite melancholy the other day looking at your old garden, & the flowers… I think the time when you & Catherine were little children & I was always with you or thinking about you was the happiest part of my life & I dare say always will be.

But Darwin, a man of rigorous daily routine, was also keenly aware of the tradeoffs between family life and work life, which he lamented facetiously in a letter to a scientist friend about to get married:

I hope that your marriage will not make you idle: happiness, I fear is not good for work.

Still, Darwin knew that science and personal happiness were complementary rather than mutually exclusive. (He wrote in The Descent of Man in 1871: “Happiness is never better exhibited than by young animals, such as puppies, kittens, lambs, &c., when playing together, like our own children.”) In a July 1862 letter to his botanist friend Asa Gray, Darwin observes this false choice with equal part wry wit and earnestness:

Children are one’s greatest happiness, but often & often a still greater misery. A man of science ought to have none, — perhaps not a wife; for then there would be nothing in this wide world worth caring for & a man might (whether he would is another question) work away like a Trojan.

Complement with this charming graphic biography of Darwin and the story of how his photos of human emotions revolutionized visual culture.