Most people think fondly of their grandmas and grandpas — the folks who spoiled you with cookies, money, or rolled out entire feasts for you whenever you came home from college. It's kind of common knowledge that grandmas are rockstars, the ones to pick up the slack when parents aren't around or doing the job. Now, a new study states there’s an evolutionary importance to the nurturing nature of grandparents: Since primitive times, they contributed significantly to their families and grandchildren when it came to food.

The study, published in Proceedings of the Royal Society B, examined indigenous people living in Bolivia in the Amazon, known as the Tsimane people. This community of people rely on hunting, gathering, or cultivating their food — and actually depend a lot on grandparents in the families to provide them with calories. While parents contributed the highest amount of calories to their families, they were followed by grandfathers and grandmothers, and finally uncles, aunts, and children over the age of 12.

“We quantified the net flow of calories among individuals in an environment where access to food is limited and depends on people generating it themselves,” Paul Hooper, an anthropologist at Emory University and an author of the study, said in a press release. “The results support the theory that grandparents are key to our relatively long childhood and long lifespan, which are a big part of what makes us human. Their efforts have likely been underwriting human society for hundreds of thousands of years.” Some evolutionary theories expound that one of the reasons why humans live much longer than other primates is because of the bolstering of resources that grandparents provide their families.

The researchers worked on gathering data for the study over five years, spending time with 239 Tsimane families from eight different villages — which are located along the Maniqui River in the Amazon rainforest. Examining their lifestyles and communities gave the researchers insight into how “humans lived before modern industrialization,” Hooper said in the press release. The Tsimane relied primarily on their own cultivated food, including cassava, plantains, rice, and corn — as well as fish, deer, tapirs, and monkeys.

The researchers examined the amount of calories each individual consumed on a daily basis, then estimated the number of calories that various family members contributed to the diet. Amazingly, the grandparents were major contributors.

Of course, it’s often easy to overlook the importance of grandparents in a modern, industrialized society, where young people are forced to become competent earlier than in the past. “Whether you’re a hunter-gatherer or an accountant, you’re good at what you do because someone supported you while you developed and learned skills,” Hooper said in the press release. “The economics of learning are what makes grandparents so important to humans compared to other primates.”

Hooper admitted he was inspired by his own maternal grandmother in his research, noting that she influenced his career choice as she earned a biology degree in the 1930s. And perhaps this study is a reminder that we should appreciate our grandparents for their support as we grew up, and even as we became adults; their wisdom and caring made us into who we are today.

Source: Hooper P, Gurven M, Winking J, Kaplan H. Inclusive fitness and differential productivity across the life course determine intergenerational transfers in a small-scale human society. Proceedings B. 2015.