Posted on Facebook, milestones such as birthdays and anniversaries prompt users to reflect on the passage of time and the patterns of their lives - and help the social media giant recycle content in order to boost engagement, according to new Cornell research.

And although these anniversaries seem like a signature product of the social media age, they stem from newspapers' tradition of printing historical events that happened "on this date," said Lee Humphreys, associate professor of communication in the College of Agriculture and Life Sciences.

"We find it helpful to look back at things; it helps us think about the patterns and rhythms in life," said Humphreys, author of "Birthdays, Anniversaries and Temporalities: Or How the Past Is Represented as Relevant Through On-This-Date Media," which published Sept. 3 in the journal New Media and Society.

"Looking back at our previous posts helps us to understand where we are today," Humphreys said. "We think about how much we've grown, how much we've changed, how our children have changed, how our relatives have changed. The past takes on new meaning based on our current experiences."

During the pandemic, reviewing past milestones or events might be particularly reassuring, Humphreys said, since they remind us that one day we'll be looking back at it.

"Given the amount of uncertainty in the world, it's helpful to look back," she said. "Whether they were good experiences or bad experiences, we came out of them, and we're still here. It gives us a sense of the longer term."

Birthdays in general are an unusual ritual, Humphreys said: We don't remember our own births, so the celebration is often tied both to reflection and our place in our families and communities. That's especially true on social media, because birthday announcements and wishes are public.

"There's a sense of social connectivity that comes from celebrating birthdays - it's something you wish someone because it's a way of reinforcing social ties and the familial unit," she said. "But the other element, when it gets translated to social media, is the performative aspect. When I wish someone a happy birthday on Facebook, I'm doing so publicly, so I'm reinforcing our social connection in front of a larger audience."

The paper grew out of Humphreys' ongoing work on how people incorporate social media into their everyday lives, and her 2018 book, "The Qualified Self: Social Media and the Accounting of Everyday Life," which compared social media to pre-digital traditions such as scrapbooking and diary-keeping.

"So much of the social media environment is about real time and this notion that time is speeding up; it's all about what's going on right now and fear of missing out and having to be online at all times," she said. "So what I was trying to do is point out different ways time is working, besides this real-time access. Comparing it to the newspaper lists was really helpful, because it's a daily cycle of what's relevant today."

"On this date" lists, compiled for decades by The Associated Press for use in publications or broadcasts, collect anniversaries of major national or international events - encouraging people to put time in perspective by remembering where they were at the time, for example. Although social media anniversaries and birthdays are far more customized to individual lives, both serve similar functions - for readers as well as the media companies.

"We often think about the social media environment as being incredibly new and different, and part of what we're trying to do in this paper is show how they are really drawing on very similar practices of 20th-century media companies: reusing material in ways that feel fresh and new," she said. "There's an economic incentive for media companies - whether Facebook or newspapers - to use historical content as ready-made new content."

The lists, and the anniversaries, also help orient us around a unit of time that is important to both Facebook and newspapers: the 24-hour day.

"To newspapers, it's their publication cycle; to social media companies, daily active users is one of their key performance metrics," she said. "For us, it's not just reminiscing about the past. It's about where I am today, and how I am experiencing this moment."