Lily and Roger's nightly dinner pairs home-cooked chicken with a medley of organic blueberries, sweet potatoes, and pumpkin. They're taking supplements for their joints and walking two to three miles twice a day. The combination of a well-balanced diet and daily exercise is impressive for a couple pushing age 65. Well, in dog years that is.

Lily, a border collie, and Roger, a German shepherd, are dogs with a caretaker who views their health as important as hers.

"I'm just like a mother hen," said Pam Hall. "I think I'm preventing the onset of any age-related diseases. I'm saving a lot on veterinary bills, and I have very healthy dogs who have a higher quality of life."

Hall admits that her way of caring might be considered "extreme." But, according to a new UNLV anthropology study, there's a precedent for it in human evolution. It may stem from how parenting developed over the course of human evolution. A UNLV anthropology survey of close to 900 dog keepers found human interactions with dogs are moving from a friendship to a parent-offspring relationship.

"We are pouring an enormous amount of money into pets such as dogs, cats and fish. We are coddling dogs more and more as emotional surrogates of kids," said Peter Gray, a UNLV biological anthropologist and lead investigator of the study.

Gray and his students, including Hall, used human parental psychology data and behavioral patterns to categorize the human-dog relationship.

What your parental status says about your feelings toward your dog:

• Adoptive -- If you obtained the dog on your own or as a joint decision with a significant other, you're more attached and have a better relationship with your dog than a dog stepparent or relative.
• Stepparents -- If your dog was acquired by a significant other, not as a joint decision, you're likely to be less attached to the dog and you put minimal effort into maintaining a relationship with the dog.
• Relative -- If your dog was obtained by a relative such as a parent or sibling, your attachment level is close to that of a stepparent.

From raising kids to canines

Through human evolution, Gray said, natural selection shaped human parental behaviors. Those parental behaviors carried over to cross-species relationships. Basically, humans seek relationships that need our tender loving care, Gray added.

"There's a lot of discussion about whether evolution equipped us with caregiving capacities," said Gray, who researches human reproductive behavior. "Nowadays we apply those adaptive behaviors to how we care for other animals, in particular dogs. So it begs the question: Why are people doing that in the first place?"

As fertility rates plummet around the world and the cost of having children increases, dogs help fill the gap for our need to care for something or someone. Trends suggest dog ownership is also popular among elderly adults who don't have grandkids nearby.

Dog ownership has always been popular among families with young kids. But, the "dog parents" aren't necessarily the mom or dad in the family because parents tend to choose dogs as pets in hopes their kids will learn to take on more responsibility, like Gray and his wife wanted for their two young daughters. Gray helped choose the golden doodle named "Puppers" and he's the one that takes him for walks. But he falls into the "dog relative" category.

"I am most attached to my kids and part of my attachment is my feeling the kids got something they really wanted - a puppy," said Gray. "My kids are most attached to the dog. But if the dog bit them or there was a significant health issue associated with keeping the dog, he would be gone - just like that. "

The study, "Raising canine: Cross-species parallels in parental investment," appears in the March 1, 2013 edition of "Human-Animal Interaction Bulletin," a publication of the American Psychological Association interest group dedicated to the study of human-animal interaction. The study authors are Peter Gray, UNLV anthropology professor; Pam Hall, Chantal Downing and Dominic Hurton of UNLV department of anthropology, Eric T. Steiner and N. Clayton Silver of the UNLV department of psychology.