An old Dodge S.U.V. roared up our driveway, horn blasting. A head popped through the driver’s window. “Your secret weapon has arrived!” shouted Tanya, our friend and veteran donkey trainer. She climbed out and stood by the backseat as I hurried out of the house.

“Brace yourself,” she warned.

In the weeks since we’d adopted Sherman, an ailing donkey who’d been liberated after years inside a filthy stall, we’d been trying to figure out how to turn him into my running partner. Tanya was a genius at nursing Sherman back to health, but when it came to getting over his skittishness, even she was stymied by the Eternal Equine Enigma: How do you persuade nature’s most stubborn creature that what you want him to do is actually his idea?

Sherman was especially tricky, because his years of seclusion made him nervous about even stepping onto the road, let alone jogging down it for miles. We were making progress, but fighting a tight deadline: By summer, we were hoping he’d be ready to race through the Rockies with me in the Pack Burro World Championship. At the rate we were going, we didn’t stand a chance.

Then Tanya had her breakthrough.

“Behold!” she said, throwing open the Dodge’s back door. There, in all its tiny glory, was the mini donkey she’d rescued from the slaughterhouse.

“Matilda!” I said. “I thought you adopted her out to some family as a horse companion.”

“Yeah, she only lasted there a day. They had a dog that came at her. Matilda kicked it so hard, its leg had to be amputated.”

Matilda hopped down out of the car. We opened the gate and she barreled inside to check Sherman out. While Matilda snuffled him eagerly from nose to tail, Sherman remained frozen and uncertain. Whatever Matilda had survived in her past, it had made her Sherman’s opposite: Where he’s calculating and reluctant, she’s curious and fearless. Matilda is also a fine runner, thanks to her jaunts alongside Tanya’s horse carriage. I could guess what Tanya had in mind, and it was more brilliant than she realized. I’ve spent years researching ancient sports and I’d come to understand that the entire history of distance running could be summed up in three words:

Packs against herds.

Humans are hunting pack animals. Long before we figured out how to sharpen sticks into killing tools, our only natural hunting weapon in the wild was our ability to team up and chase other animals until they collapsed from heat exhaustion. We’re fantastic at sweating out heat, and that gave us a tremendous advantage against creatures that can cool off only by panting.

Donkeys are prey, so they live or die by the herd. Like antelope, a donkey’s best hope of surviving an attack is by sticking tight to its mates. Even when stampeding, donkeys run side-by-side, maintaining formation to prevent an attacker from pulling one of them down.

Out there on the savanna, it’s gang warfare, pack versus herd. No human could run down an antelope alone, and no antelope was safe if it broke from the group. Survival was a numbers game for both predator and prey: The bigger your posse, the better your chances. Nowadays, we like to romanticize running as a solo sport, each of us slapping along to the heroic echo of our solitary footsteps, but our ancestors knew that in nature, a solitary runner is doomed.

Maybe that’s why, today, we feel the weird urge to shell out hundreds of dollars for the privilege of running 26.2 miles surrounded by 50,000 strangers. Logically, there’s no reason you can’t just scoot out the door and run a marathon on your own without spending a dime. That urge to gather suggests the hunting pack is still in our DNA. It also may be why you can work out twice as long with a buddy while feeling much less pain.

For Sherman, I was hoping for something even better. I didn’t want him to just tolerate our runs; I wanted him to love them, finishing each one happier than when he started. I’d read that group exercise had an additional surprising effect: Instead of making people more hyped and competitive, it actually reduced stress and left them calmer. Maybe teaming Sherman up with another donkey would not only improve his running but also his peace of mind.

We were all set to try until Tanya pointed out a problem: She doesn’t run. “Oh good God,” she said. “I’d die.”

I went inside to see if I could recruit my wife, Mika. She was raised in Hawaii and is more about hula and her ukulele than running. But as soon as she met Matilda, Mika was in.

Tanya led us all out to the street. “Walk on,” she commanded and Matilda was gone, breaking into a trot so quickly that Tanya barely had time to hand the rope to Mika. Sherman’s nervousness vanished just as quickly. He was still scruffy and barrel-shaped from being locked in a stall for so long, with bald patches in his fur where Tanya had shaved off dried dung. But beneath his prison pudginess was a wild spark. He snorted and galloped like a zebra until we pulled even with Mika and Matilda.

“Bring ‘em back,” Tanya called.

She heaved a saddle on to Flower, the big riding donkey she’d hauled in her trailer just in case, and climbed aboard. Matilda, fearless as always, pushed ahead to take the lead, with Sherman squeezing in beside her. “Ready for some fun?” Tanya asked. “Looks like they are.” She gave a command and we were off, all six of us clattering and padding along, finding our way in the pack.