Facebook is increasingly in the crap these days. From revelations that 2 billion user profiles were sold for commercial and political gains - to the very nature of social media being damaging to your mental health.
So how can a website cause psychological harm - especially one designed to populate your screen with updates and photos from friends?
Humans Evolved for Social Connection
Human beings have profound social needs. In evolutionary terms, we spent more than a million years living in tribal communities maxing out at 150 members.
This is known as Dunbar's number: the average number of friends and acquaintances we can keep before those relationships start to lose meaning.
The human brain evolved to operate within physically and emotionally supportive tribes. They helped us develop into adulthood, find a mate, raise our offspring, and receive care in our old age.
These behavioural adaptations are embedded in our DNA, so that we intuitively yearn for a close community of friends and family. We do it to survive.
Yet according to Johann Hari, author of Lost Connections: Uncovering the Real Causes of Depression - and the Unexpected Solutions, Western society increasingly fails to provide this tight-knit community.
When you're young, you get to be pretty much carefree in your life while the grown ups watch out for all your physical and social needs.
But once you become an adult with a career and a mortgage, you have to put significant effort into maintaining social connections on a consistent basis. That's because they're generally not automatic in our busy modern society.
Then you have kids. And a hundred distractions come along to compound the issue.
You begin to consider a social life as a luxury and not an essential. You go from zero responsibility in childhood, to complete autonomy in adulthood, to the intense responsibility of having your own kids.
All this occurs within the modern framework of separate nuclear families and non-tribal living.
Johann Hari argues that in order to stay psychologically stable and secure, you need face-to-face contact with your community on a daily basis.
Without it, you're going to feel isolated because there's something important missing from your life.
Then comes the neurochemical imbalance. When your social needs are unmet, your brain responds with withdrawal and despair, culminating in major depression.
See Dr Robert Sapolsky's A Primate's Memoir: A Neuroscientist's Unconventional Life Among the Baboons. Like your primate ancestors, you can become permanently anxious and depressed, feeling rejected by your hierarchical tribe, and plan to go away to die.
What a relief it was, then, when Facebook introduced a screen onto which you could project your personal network. To prove to yourself that you are indeed connected. And to actively link you in to that tribe on a minute-to-minute basis.
Except for one problem. The commentaries and likes exchanged with your friends on Facebook pale in comparison to the emotional and social bonding of the face-to-face relationships with which we evolved.
Real social connection involves responding to hundreds of subtle social cues. Such bonding is only possible when you're close enough to smell the other person.
Take away the proximity, the social cues, the human interface, and you're no longer talking to your friends.
You're talking to a screen.
Humans Evolved for Social Approval
Let's examine that tribal system that kept us safe for thousands of generations.
There are rules to tribal living, designed to keep the community safe from within. And everyone knows everyone else, so personal accountability is high.
You can't steal from or abuse other people in the tribe or you'll become known as Jerry the Thief or Mary the Murderer. You'll be ostracised. Your essential tribal support will disappear, and you'll be less likely to survive.
The flipside of that is the need to establish yourself as a warm, trustworthy, skilled, strong, intelligent member of the community. You do this through nurturing relationships within the tribe, and displaying a host of discrete social signals.
Meanwhile, you make your own judgements about your tribal acquaintances. You closely watch their social signals.
Is this person a potential ally? Is this competition? Is this a mate? Are they trustworthy? Are they disingenuous? Will they cooperate? Will they enlighten me?
Naturally, then, you're hardwired to seek out social approval, to rank as highly in the tribe as you can, so as to generate more support, more resources, and more offspring.
These are all fundamental instincts driven by your genes - see Richard Dawkins' classic The Selfish Gene, which depicts a gene's-eye-view of evolution.
So where does this social approval meet the psychology of Facebook?
Facebook feeds your hunger for social approval by having you engineer stories about yourself and receive digital likes in return. It's quite on the nose when you think about it: we actually click a button that says I like this thing you did.
The approval triggers that long-evolved dopamine rush, a biologically-programmed buzz that reinforces your desire to seek it out again in future. And so, like hundreds of millions of other human beings, you get swept up the in Facebook addiction.
A hardcore Facebooker engineers stories about the quality of food they eat, the calibre of people they socialise with, the exotic places they travel, and - of course - how attractive they look while doing it.
Imagine a caveman doing this. He's showing off his resources and advertising himself as a superior mate. He'll gain authority among the other males, and desirability among the females of his tribe.
When you do this, your social engineering efforts accrue likes and comments, and in return you gain social validation from your digital tribe.
Except it's still all an illusion.
In social media transactions, there are no voices, no smiling, no pheromones, no contact; none of the social cues to which you have evolved to respond.
If face-to-face social approval is like eating a delicious meal with real enjoyment and nourishment, then Facebook approval is like sniffing that meal: a mere tease.
The effects aren't visceral or long lasting, and you're left sitting there alone holding your black mirror.
So much effort for so little reward. Why do we insist on doing this as a lifestyle choice?
The Slippery Slope of Addiction
One of the reasons we do this is because social media is highly addictive. Facebook creators deliberately employ psychological tactics to make their apps as addictive as possible.
For example, opening Facebook on your phone is predominantly a result of unconscious psychological conditioning.
Without really thinking about it, you habitually pick up your phone in a moment of boredom and click on the little blue square to get your next dopamine hit.
Infinite scrolling and video autoplay extend your experience so that you can spend long periods of time interacting with Facebook through no conscious choice of your own.
Take push notifications. Facebook leverages the proven most powerful type of operant conditioning: variable ratios of enforcement. They hit you with notifications that range from desirable (a video of your best friend being bitten by a monkey), to neutral (an acquaintance posts 37 more photos of their kid on a slide), to downright annoying (a stranger posts a dumb rant to a group you forgot you even belong to).
There's no way of telling if these notifications are going to be good, bad or neutral, and this unpredictability compels you to make the click to find out. Again, you're suckered in to spending precious time building artificial relationships via your screen instead of real relationships via reality.
This is a dangerous idea. Not only have we forgotten the importance of community, but Facebook and other social media compound that. They trick us into investing our time and social efforts where the rewards are few.
The social engineering to which you're addicted creates even deeper levels of psychological unrest.
Whether you're conscious of it or not, Facebook is a platform for you to define your ego, which makes your profile an ad for yourself.
Take your head shot: a literal expression of your identity. Then your cover photo: affording a more abstract expression of your advertised lifestyle.
Facebook urges you to select your five best photos to show off your attractiveness, social standing and resources, and your number of friends to show off your social success. In doing so, Facebook has attempted to recreate the real-world social signals on which human beings have evolved to rely.
Except, we now know that these signals are illusory. It may hurt to acknowledge that everything you do on Facebook is engineered. But it's true; the same way your real world choice of clothes, hairstyle and makeup are also engineered to gain social validation.
You're a social creature. You care about what others think. Even if you say you don't. Deep down, you absolutely do. Psychopaths excluded. You need to be socially accepted in order to have a successful life and produce offspring. It's human nature.
Of course, social media engineering is a lot easier to fake than real-world social cues, and this is where we start to kid ourselves.
My Android phone has automatic photo enhancement features like "skin tone", "slim face", and "large eyes". I can take 10 selfies, choose my favourite, and then stick a filter on it for further enhancement. At what point does this no longer portray the real me?
Social media users are so uncomfortably aware of this selection and enhancement process as to use accompanying hashtags like #nomakeup or #nofilter.
The identity-forging nature of Facebook makes it an ideal haven for narcissism and attention-seeking behaviour.
Status updates are an oddly public display of private thoughts and emotions which we would never declare to a room full of hundreds of people in real life.
It also creates artificial rules for interaction. These can be played up by pastimes such as vaguebooking, where people seek out the attention (but not the two-way intimacy) of real social interaction.
Are we all out-and-out narcissists for becoming addicted to social media?
It's more fitting to say that people fall on a spectrum of narcissism, and social media provides a convenient stage for expressing varying degrees of self-interest.
You don't have to scroll far down your newsfeed to see examples of it: the engineered selfie, the thinly veiled brag, the materialistic boast, the attention-seeking rant. Younger people do this a lot more than older people, and this comes down to ego.
Frequent selfie-posting on social media has been studied by social psychologists. It reveals your personal identity resides in its formative stages.
Selfie-posters have an ego that's primarily derived from extrinsic factors - namely the impressions you make on other people. Selfies are merely opportunistic advertisements for enhancing self-identity.
But a selfie isn't a real expression of identity. It's a carefully pruned, computer-manipulated one.
What happens when you look in the mirror and don't see the toned-up, slimmed-down face you have advertised to the world via Facebook?
You succumb to Impostor Syndrome.
Impostor Syndrome is really common. It's the psychological trait of doubting your own accomplishments and having this uncomfortable feeling that one day someone's going to expose you as a fraud.
I used to write a website about lucid dreaming and accrued millions of visitors. People wrote me lovely fan mail as if I were some kind of all-knowing deity. But in my head, I deflected every bit of praise with the thought that I'm just a flawed human being like everyone else.
There was no way I could live up to the polished persona I'd created on my website, which contrasted significantly with the fallible version of myself I've known all my life. Derren Brown details this personal conflict in Happy: Why More or Less Everything Is Absolutely Fine and humbly explains the difficulties celebrities face when confronted with their fans in the real world.
In a similar way, selfies promote Impostor Syndrome by falsifying your looks to the world in a way that is irreconcilable with reality.
You could be an attractive person, maybe even a supermodel, but without the careful planning, posing and digital enhancements, you find comparative ugliness in the harsh light of the bathroom mirror.
In response, your self-esteem takes a blow, not only undoing the temporary dopamine boost generated by your selfie likes, but undermining your real-world attractiveness (which means a lot to you as a prolific selfie poster in the first place).
Deep down, it's a no-win situation and best avoided.
The Psychology of Facebook
Yet people love Facebook. It's a daily ritual for hundreds of millions of people around the world. And that tells us Facebook has tapped into a deep human need for social connection.
But does it deliver? Are we just fooling ourselves?
I'd argue that Facebook actively damages your self-esteem by having you engineer an idealised version of yourself you simply can't live up to.
It also pits you in battle against other people. You unconsciously slip into a lose-lose competition of who has the best looks, the best material possessions, and the best lifestyle.
These are things Johann Hari calls junk values. Like junk food, junk values don't nourish or enhance your well-being, and the effects are potentially damaging in the long run.
One sure sign you're engaged in this junk value contest is if you've ever used the oxymoronic #humblebrag.
Even worse though, Facebook distracts you from forging the real-world social bonds which are critical to your mental health, all the while portraying itself as a source of such richness.
Think of your most prolific Facebooker friend. Do you really think more of them in reality for all their social engineering efforts?
They may portray supermodel qualities on Facebook but contrast that to their real self, warts and all. It's an odd letdown. It's like an impossibly perfect Burger King billboard photo to its sloppy real-life counterpart. What if puffing yourself up on Facebook is analogous to advertising? The actual product can't possibly live up to the sales hype.
And what's the moral moral of this story?
Perhaps you should view your Facebook profile for what it is: a social advertisement that conveys why you think people should like you.
Far from being a light-hearted photo feed bringing people closer together, Facebook is an infinite ad feed that could well be tearing us apart.