How do you make a grown man cry? A swift kick in the gonads might do the trick, but if you're more of a long-game player, you might prefer to lend him a copy of Marley and Me, the memoir by the Pennsylvania journalist John Grogan of "life and love with the world's worst dog". "I've heard from police officers, firefighters, construction workers," says Grogan, "men who wouldn't want to be seen crying over a death in the family, or on the job, because it would show weakness. And they all tell me they wept like a baby at the end of the book."
Marley and Me, about Grogan and his young family's experiences with the titular Labrador, was first published in 2005. The book sold six million copies, and has now been made into a movie starring Owen Wilson and Jennifer Aniston as Grogan and his wife Jenny. It's also the pre-eminent example of a publishing phenomenon – pet lit.
Last month, Vicki Myron's pet memoir, Dewey: The Small-town Library Cat Who Touched the World, was published in the UK after making it to the bestseller lists of The New York Times, Publishers Weekly and The Wall Street Journal in the US at the end of 2008. Dewey, a friendly fur-ball found in a returned books slot at the library in Spencer, Iowa, was adopted by Myron, the library director. He became an international celebrity before his death, aged 18, in November 2006. Meryl Streep is set to play the author in a film version of the cat's life.
On this side of the Atlantic, we have Endal: How One Extraordinary Dog Brought a Family Back from the Brink, also published in February. The 1991 Gulf War veteran Allen Parton was embittered by his injuries, which left him unable to walk, talk or write – until he bonded with Endal, a young Labrador who'd failed his training as a disability assistance dog.
A quick look at the list of such titles published since Marley confirms the trend: there's Walking Ollie: Winning the Love of a Difficult Dog; A Dog Year: Rescuing Devon, the Most Troublesome Dog in the World; The Bad Dog's Diary: A Year in the Life of Blake, Lover... Fighter... Dog; Rescuing Sprite: A Dog Lover's Story of Joy and Anguish; and My Life with George: The Inspirational Story of How a Wilful Dog Brought Joy to a Bereaved Family – to name but a few.
Of course, there have been highly successful animal-themed novels in the past, but the bestseller lists are new territory for non-fiction family pets. "The Horse Whisperer  was one of the most extraordinary publishing events ever," says the literary scout Louise Allen-Jones. "Nicholas Evans received what was then the highest ever advance paid for a novel. That was about the relationship between a horse and a girl, and how they could rescue one another. The trend isn't exactly new, but it's turning up in slightly different guises now, and there's a lot more of it about than there was 10 years ago.
"Wolves have featured in several. There has been a book about a tortoise. There's even one about hedgehogs... I'm hoping that pet memoirs will replace misery memoirs on the bestseller lists. Maybe animals are going to cheer us all up."
There are signs that this may, indeed, be the case. Hodder, the UK publisher of both Marley and Dewey, previously had misery-lit hits with the likes of Ugly by Constance Briscoe, Shame by Jasvinder Sanghera and Broken by Shy Keenan. Endal has been published by an imprint of Harper, home to such harrowing child-abuse chronicles as Damaged and Don't Tell Mummy: A True Story of the Ultimate Betrayal.
But, as pet-lit proves, life lessons needn't be delivered in such a harsh fashion. Animals are exemplary guides to being human. Dewey, Myron says, "didn't care what you looked like, what you smelt like, what colour you were, how much money you had. If you wanted to cuddle, so did he." The more difficult Marley taught Grogan the importance of commitment, he says. "It would've been easy to give up on that big, crazy, hard-to-manage dog, but we stuck with him and it was a really rewarding relationship."
As Pen Farthing discovered when he travelled to Afghanistan to work with the country's canine population, bonding with a pet is a universal experience. In his new book, One Dog at a Time: Saving the Strays of Helmand, he describes how, after British soldiers befriended stray dogs and took them on patrol, they found the locals far more responsive and sympathetic.
In such serious times, it may seem frivolous to be buying books about Labradors, but, says Grogan, "the human heart is large and complex and, if anything, I think having a pet makes us better humans – more empathetic, kinder, more generous-spirited and responsible. It enhances the human experience, rather than detracts from it. I don't think it's frivolous at all."
The film 'Marley and Me' opens on 11 March; 'Dewey: The Small-Town Library Cat Who Touched the World' (Hodder) is out now