You don't have to carry a club or wear a bearskin to live like a caveman. To keep fit, a number of people have adopted the "Paleo" lifestyle -- eating and exercising like our ancestors from the Paleolithic era.
Art De Vany, 73, is often called the "grandfather" of the Paleo movement. For De Vany, a workout includes pulling his Range Rover in his driveway.
He compared it to "hauling heavy bison out of a pit."
"If you think about it, you're using every single muscle in your body. You're not going to hurt yourself by overdoing repetitions," he said. "It's easy for me."
De Vany, the author of "The New Evolution Diet," also eats like a caveman by consuming meat, seafood, vegetables and fruit, but no grains or processed food. He adopted the caveman or Paleo diet some 30 years ago in an effort to improve the health of his family.
The human species during the Paleolithic age, he said, "was probably the epitome of the expression of the human genotype. (They had) large, powerful brains -- they gave us all that we have in our world."
Those big-brained cavemen ate meat, vegetables and nuts. What they didn't eat, besides processed foods, was bread, grains, rice or anything that is the product of agriculture.
Actress Megan Fox is rumored to be a fan of the diet, and experts seem to have no major problems with it because it balances meat with a lot of fresh vegetables.
"I know many, many people who swear by the caveman diet," said nutritionist Danielle Omar. "I would say that if they're able to maintain it, and they're choosing lean meats, and they're really watching the fat, then ... it's okay for them."
The diet's rejection of processed foods "is positive," said nutritionist Keri Gans. "The average person should be staying away from more processed foods."
Robb Wolf is another adherent to the Paleo lifestyle. Wolf, the author of "The Paleo Solution," runs a gym in California -- but it's not your average gym.
"Usually when people walk in, initially they're not sure if it's an automobile chop shop or what exactly it is," he said.
The gym's equipment includes gymnastic rings, pommel horses and cargo nets for climbing.
"We're not scratching around under bushes and getting poison oak on us in weird places and stuff," Wolf said. "It's trying to make full-body, functional movements that are fun."
"We do it in a group format," he added. "I think a lot of the success for my gym and a lot of gyms like it is there is a tribe element to it."
At the gyms, they love the tribe.
"You come in and you're accepted for who you are, and then immediately challenged to get better," said David Osorio, the owner and head coach of Crossfit South Brooklyn, a gym in Brooklyn, N.Y.
The members of this community work together and play together. Seventy people recently took part in the gym's "Paleo Challenge," which included following the Paleo diet for two months and coming together for a potluck dinner where the food was all Paleo, all night.
Wolf, amazingly, was a vegan before he went Paleo.
"I ate a vegan diet for two years and I got down to 135 pounds and couldn't lift my own body weight on the bench press. But the interesting thing is I was so sold on the idea of this being healthy that I wasn't listening to all the feedback that my body was giving me," he said.
Now he travels the world as a champion of meat. He claims he's convinced nearly a million people to follow the caveman lifestyle -- and, he says, it's not just "the lunatic fringe" who are following his lead.
"It's cops and teachers and doctors and computer programmers," he said. "It's everybody."