ABC News' Juju Chang and Mary Pflum report:

Rory Delaney is a three-year-old who has not been out of diapers that long, but she already knows something about changing them.

Her sister, Saorise, is a five-year-old kindergarten student who already knows what she wants to be when she grows up, a mom.

Now, researchers at Rockefeller University say the inclination that both Rory and Saorise feel at such a young age to nurture and feed their baby dolls and play with items like strollers could be something they were born with, and something that will definitely impact their futures.

In a study with mice, the researchers determined that a single gene exists that could be responsible for motivating mothers to protect, feed and raise their young.

The study's findings mean there could be a valid explanation as to why some women seem born to be maternal figures, while others come across as detached or cold or even completely not interested when it comes to children.

Some are calling the discovery the "mommy gene."

Moms who spoke with ABC News were divided on the possible link to motherhood, with some saying it makes sense and others saying it is not that simple.

"I can always remember playing with dolls and always thinking, 'I'm going to be a mom,'" said Melissa Delaney, a mother of three. "I do have friends who say they just don't have it in them to want a baby or to take care of them."

"On a good day I'm incredibly nurturing. On a bad day, it's a little harder," said Julie Taw, a mother of two, raising the argument that maternal instinct may have more to do with circumstance than genetics.

One blogger who leads a parenting website worried the gene study might present mothers with another reason to look harshly on themselves, and other moms.

"I worry that it could almost invite us to look at someone that does something differently than we do and say, 'She doesn't want to breastfeed. She doesn't have the 'mommy gene,"" said Melissa Lawrence, a mother of five and co-founder of CloudMom.com.

Do you think a "mommy gene" exists? Tell us what you think by weighing in below in the comments section.