Making friends can seem easy when you're young. You encounter more new people and have more free time when you're first venturing out into the world than when you're more likely to be settled down with a steady job, a long-term partner and children.
New research suggests that our social networks may shrink from when we're about 25, after which we tend to lose more friends and acquaintances than we gain. But there's also an important difference between men and women, with men likely to make more contacts in their youth but lose them more rapidly as they age.
The study, carried out by scientists at Oxford and Aalto universities and published in Royal Society Open Science, looked at the phone call records of 3.2m mobile users across in Europe. Collected in 2007, the data included the age and gender of the mobile users and the people they called, how often they called each person and the length of each call.
Downhill from 25
The research showed that people aged 25 and under talked on their phones more than any other age group, which suggests that people might become less socially connected with age. This echoes other research on face-to-face social networks that suggests that our social networks shrink as we age.
The big life events that usually come with age, such as marriage and parenthood, lead people to invest more of their time socialising with just a few close family members and friends. Later in life, retirement, health issues and the death of partners and friends can leave people socially isolated, although this can sometimes inspire older people to engage more with their community through volunteering and religious participation.
But there could be other explanations for the fact that older people tend to call fewer friends on their mobiles. For one thing, older adults use mobile technology far less than younger people, and the new study didn't capture data on landline phone calls and meeting in person.
Things also get more complex when you look at the data by gender. Among the under 40s, men contacted more people than women, but after 40 this gender difference reversed. And even though younger men made calls to more people than women, women spent more time talking to the people they called.
Again, these patterns mirror what we've learned from studying other kinds of social interaction, including face-to-face meetings. Women tend to invest more time in one-on-one interactions with others, whereas men tend to prefer interacting in groups. Our evolutionary roots may drive these differences: In our evolutionary history, females relied on their partners and a few key people to assist with child rearing, whereas males were attracted to larger groups that could help with hunting.
The other pattern that emerged from studying the mobile phone records was in the people receiving the calls. Under 40s most often made calls to people their own age, while those aged 50 and older frequently called people a generation younger than them. The researchers speculated that this may be the result of older adults mostly using mobile phones to call their adult children - who may have even bought their parents their mobile phones.
Perhaps unsurprisingly, each person's most frequent and longest calls tended to be with an opposite-sex person who was the same age - most likely their partner. Taken together, these findings suggest that people were socialising the most with their partners and family members, particularly in older generations.
There are limits to what mobile phone data can tell us about people's relationships. In this case, the researchers could only speculate about whom participants were contacting based on their age and gender. Mobile phone use has changed dramatically in the years since these data was collected, and people increasingly use messaging apps such as WhatsApp to communicate. And even though people frequently socialise on their mobile phones, our screen time still only represents a small sliver of our social behaviour.
But this research does suggest that the way we use our mobile devices to connect with others changes throughout our lives, in much the same way other forms of social behaviour do. Humans have a strong need to seek connections with each other but we adapt the way we fulfil this need to our changing life circumstances.