For better or worse, many of us never forget high school: the unrequited romantic crushes, chronic embarrassment, desperate struggles for popularity, sexual awakening, parental pressure and, above all else, competition - social, athletic, academic.
There's even an entire genre of entertainment that revolves around high school. Beverly Hills 90210, Mean Girls, Heathers, The Breakfast Club and Fast Times at Ridgemont High all revisit the conflict and angst of these years. What is it about this period of our lives that makes it seem more meaningful and memorable than any other?
My research experience as an evolutionary psychologist leads me to believe that many factors interact to make our teenage memories so vivid.
But the main driver is the collision between the hardwiring of our brains that took place across several million of years of evolution and the odd social bubble created by high school, which poses an unprecedented social challenge to our prehistoric minds.
In other words, the world that we evolved to be successful in (a small, stable group of interrelated people of various ages) is very different from the holding pen full of teenagers brimming with hormones that populate our world during the high school years.
The reminiscence bump
Some look back on high school as the best time of their life and pine for those 'good old days'. Whether or not this was actually the case, it turns out there may have been some evolutionary advantages to having a rosy view of the past.
But most of us remember high school with an emotional mixture of longing, regret, joy and embarrassment. And strong emotions equal strong memories; even the music from those years gets imprinted on our brain like nothing that comes later.
Memory researchers have, in fact, identified something called the reminiscence bump, which shows that our strongest memories come from things that happened to us between the ages of 10 and 30.
What is it about this time of life that makes it stand out from the rest of our years? Part of it is undoubtedly due to changes in the brain's sensitivity to certain types of information during adolescence. Emotions signal the brain that important events are happening, and the teen years are chock full of important social feedback about one's skills, attractiveness, status and desirability as a mate.
This is precisely the stuff we need to pay attention to in order to successfully play the cards we have been dealt and to become socially and reproductively successful.
A dog-eat-dog world
Memory research may offer hints about why the mental snapshots of our high school years remain so vivid even decades later. But evolutionary psychology can also help explain why so much meaning is attached to these years and why they play such an important role in who we become.
For example, there's a reason teenagers often strive to be popular.
As far as scientists can tell, our prehistoric forebears lived in relatively small groups. Most people would live out their entire life in this group, and one's social standing within it was determined during adolescence.
How much one was admired as a warrior or hunter, how desirable one was perceived to be as a mate and how much trust and esteem was accorded to one by others - all of this was sorted out in young adulthood.
A person deemed to be a loser at 18 was unlikely to rise to a position of prominence at 40. Thus, from an evolutionary perspective, the competition of the teen years had lifelong repercussions.
Of course, today, those who have unsavory high school experiences can move to new places after graduation and start over. However, even though we may be consciously aware of this (to the extent that we are consciously aware of anything when we are teenagers), the psychological buttons that get pushed in the adolescent brain make us become consumed with our social lives during this period.
Popularity can become an obsession, since you'll be ranked against the people in your own age cohort for the rest of your life. After all, your status as an adult primarily depends upon how you stack up compared with them, not with others.
Also, strong pressures to conform ensure that you do not stray too far from a friend group's values. Ostracism from the group in prehistoric times was tantamount to a death sentence.
John Philip Green/flickr, CC BYIt all requires forging alliances and demonstrating loyalty to others. The result is a splintering of the social world into competing cliques that grind each other up in the gears of the social hierarchy.
Mum, stop bugging me!
Back home, conflict with parents is usually inevitable. Parents want their children to succeed, but they usually have a more long-term perspective than that of their teen.
So the things that the parent thinks that the child should be concerned with (preparing for a career and developing important life skills) and the things that the child is emotionally driven to actually be concerned with (being popular and having fun) are often at odds. Parents usually realise where the parent-offspring tension comes from. Kids don't.
Meanwhile, hormones fuel the sort of 'showing off' that would have increased one's attractiveness in early societies. In young men we still reward, to some extent, the things that would have been essential for success in hunting and combat thousands of years ago: the willingness to take risks, fighting ability, speed and the ability to throw with velocity and accuracy.
Young women will showcase their youth and fertility. Beauty, unfortunately, continues to be a significant criterion by which they are judged.
Reunion angst
In earlier times, because you had a personal connection with nearly everyone in your group, the ability to remember details about the temperament, predictability and past behaviour of peers had a huge payoff. There would have been little use for a mind designed to engage in abstract statistical thinking about large numbers of strangers.
In today's world, while it is still important to keep tabs on known individuals, we also face new challenges. We interact with strangers on a daily basis, so there's a need to predict how they'll behave: will this person try to swindle me or can he or she be trusted? Is this someone important that I should get to know or a nobody that I can safely ignore?
It's a task many of us find difficult because our brains weren't really wired to do this, and we fall back on cognitive shortcuts, such as stereotyping, as a way to cope.
Natural selection instead shaped an innate curiosity about specific people - and a memory to store this information. We needed to remember who treated us well and who didn't, and the more emotional the memory, the less likely we are to forget it.
It's tough to forget when the person you thought of as a close friend publicly snubbed you, or the time that you caught another trusted friend flirting with your boyfriend or girlfriend.
The result is a strong propensity for holding grudges. It protects us from being taken advantage of again but can also make for some uncomfortable, anxiety-inducing moments at high school reunions.
To further complicate things, high school is probably the last time in life when people of all sorts are thrown together for no other reason than they are the same age and live in the same area. Yes, high schools are often segregated by economic background and race. But most high schoolers will still encounter more day-to-day diversity than they will later in life.
After high school, studies have shown that people begin to sort themselves out according to intelligence, political values, occupational interests and a wide range of other social screening devices.
At the same time, however, the people you knew in high school remain your default group for engaging in social comparison.
According to Social Comparison Theory, we figure out how good we are and develop a sense of personal worth by comparing ourselves with others; the more similar those others are, the better we can gauge our own strengths and weaknesses.
Because your high school classmates will always be the same age as you - and because they started out in the same place - there's inherently a degree of interest in finding out what happened to them later in life, if for no other reason than to see how your own life stacks up.
Given all this, it's no wonder that the English Romantic poet Robert Southey once wrote that the "the first 20 years are the longest half of your life, no matter how long you might live".
Frank T. McAndrew, Cornelia H. Dudley Professor of Psychology, Knox College
This article was originally published by The Conversation. Read the original article.