NEW YORK (AP) \u2014 It\u2019s the season of giving thanks \u2014 and it turns out humans have been doing it for a long, long time.<\/p>\n\n\n\n
As more researchers dig into the science of gratitude, they\u2019ve found the feeling likely played a key role in helping our ancestors band together and survive.<\/p>\n\n\n\n
That legacy continues today, as being in the mood for gratitude shapes who we are as a species and how we connect with the people around us.<\/p>\n\n\n\n
\u201cThis is something that is part of our human DNA,\u201d said Sarah Schnitker, a psychologist at Baylor University. \u201cIt is a glue, in a sense, that holds us together.\u201d<\/p>\n\n\n\n
Humans are social animals. That\u2019s how we\u2019ve lasted so long; not by being the biggest or the strongest, but by figuring out how to work together.<\/p>\n\n\n\n
A key part of building relationships is the idea of reciprocity: \u201cIf you like me and do nice things for me, then I like you and do nice things for you,\u201d said Michael Tomasello, a developmental psychologist at Duke University.<\/p>\n\n\n\n
The animal kingdom has some parallel give-and-take behaviors, said Malini Suchak, an animal behavior researcher at Canisius University. In experiments with\u00a0capuchin monkeys<\/a>\u00a0and\u00a0chimpanzees<\/a>, Suchak found the primates became more willing to help out a partner if that individual had helped them in the past.<\/p>\n\n\n\n Some scientists think the feeling of gratitude evolved to keep the helping exchanges going. In other words, if you were helped, you\u2019d feel like you should repay the debt with a good deed in return, said Jenae Nelson, who researches gratitude at Baylor and Harvard universities.<\/p>\n\n\n\n \u201cThis give and take \u2014 this is very, very primal and very important to a cooperative society,\u201d Nelson said. \u201cOtherwise, you just get a culture of takers.\u201d<\/p>\n\n\n\n In animals and in humans, these aren\u2019t always one-to-one transactions. Sometimes, an ape that gets groomed by another will later back that partner up in a fight, Suchak said, showing that reciprocity might not be about keeping exact scores, but forming broader emotional ties.<\/p>\n\n\n\n Though we can\u2019t \u201cspeak chimp\u201d well enough to know if they\u2019re actually saying thanks, Suchak added, it makes sense that some form of this social debt showed up early in our lineage.<\/p>\n\n\n\n \u201cIt didn\u2019t just pop out of nowhere when humans evolved,\u201d Suchak said.<\/p>\n\n\n\n Thousands of years later, gratitude has taken root in humans.<\/p>\n\n\n\n Studies have found gratitude may show up in a few spots in our genes<\/a> and brains<\/a> \u2014 including ones linked to social bonding, feeling reward and seeing other people\u2019s point of view.<\/p>\n\n\n\n And the feeling emerges early on: Children as young as 2 and 3 demonstrate they want to return favors, said Amrisha Vaish, who studies moral development at the University of Virginia. At age 4, children also show a tendency to \u201cpay it forward,\u201d she added.<\/p>\n\n\n\n In a study<\/a>, Vaish found that when kids got help completing a task \u2014 in this case, finding a key to unlock a box of stickers \u2014 they were more likely to share their sticker reward with a new person.<\/p>\n\n\n\n It\u2019s that kind of behavior that shows gratitude is more than simple exchange, Schnitker said. It can make us more generous with other people in general \u2014 even if they didn\u2019t help us first.<\/p>\n\n\n\nAnd how we stayed grateful<\/h2>\n\n\n\n