The very reason I write is so that I might not sleepwalk through my entire life.

Here’s the quote you were looking for, from Zadie Smith (born Sadie Smith):

“The very reason I write is so that I might not sleepwalk through my entire life.” 

It’s a profound reflection on writing as a way to stay present, aware, and engaged—rather than drifting through life unconsciously. 

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In female mammals the costs of pregnancy and milk

production are especially high, amplifying the difference

between male competitiveness and female choosiness. For

example, the minimum investment human female ancestors

could have made in their offspring would have been a nine-

month pregnancy followed by at least a couple of years of

breast-feeding. The minimum investment our male ancestors

could have made in their offspring would have been a few

minutes of copulation and a teaspoonful of semen. (For most

male primates, that is not only the minimum, but the average.)

Females could have produced a child every three years or so.

Males could have produced a child every night, if they could find

a willing sexual partner. This theoretical difference often plays

out as a practical difference. In hunter-gatherer societies, almost

no woman bears more than eight children, whereas highly

attractive men often sire a couple of dozen children by different

women.