From election campaigns to dishonest monkeys: Why we're hard-wired to lie

In what will likely be remembered as the most surreal election campaign in modern American history, one word has been thrown around more than most — liar. 

Whether it's Donald Trump accusing Hillary Clinton of being a "world-class liar" or Clinton saying that Trump's political career is "founded on [an] outrageous lie", dishonesty has been a major talking point of the 2016 presidential contest. 

But lying is simply human nature. In fact, a wealth of research in evolutionary biology and psychology suggests that the entire essence of being human involves lying. 

Why do people lie? 

Let's face it: we have all lied, sometimes grievously so. The average person lies twice a day (or more) and often doesn't even know it. 

 According to McGill University's Victoria Talwar, there are two main categories of lies: deceptions that are motivated by self-interest and lies that are designed to benefit others.

"To get out of trouble, to escape negative consequences, for personal gain" said Talwar, or "lies that are told to benefit other people."

You can literally lie to yourself, too. This is a unique trait of being human: no other animal has been shown to be able to deceive themselves. You might be convinced that you're way smarter than your boss or that you're terrible at a sport you actually excel in. These lies are closely tied to our self-esteem, both positive and negative.

Can other animals lie? 

In fact they can — and they do almost as often as we do. 

A study that was published a few years ago by researchers at Trinity College Dublin looked at 24 primate species and found that many of them are capable of deception. Take for instance the capuchin monkey: these adorable little Amazon dwellers have been known to lie quite a bit.

So how do you measure monkey lies? It's pretty simple, actually. In a study done by Stony Brook University, researchers observed capuchins of a low social rank repeatedly sounding the alarm of a predator nearby. They also noticed that this occurred most frequently around mealtime, when lower status individuals might not get their fair share of food. Once the alarm is sounded the low-status monkey gets to rush in and steal food while the rest of the troupe is fleeing the so-called predator.

And the Trinity College Dublin study found something surprising, too. Of the two dozen species of primates observed, the ones that were the most deceptive were also the most cooperative.

What's the link between deception and cooperation? 

This goes to an evolutionary theory that states that lying is simply a part of being in a social network.

Cooperation is the one thing that makes it possible to cheat. Cheaters have to walk a very fine line: you have to be able to gain from the cooperative behaviours of those around you... but not cooperate yourself. In other words, you have to gain the trust of your group while at the same time manipulating that trust for your own gain. 

If you lose the trust of your group, you lose the ability to lie effectively. Think of it as "the boy who cried wolf" effect. 

Is honesty always the best policy? 

Honestly, yes. That's at least what the science says. But that's only because our lying behaviour is limited by punishment. Without consequences for trespassing on trust, it is true that the fabric of society becomes worn thin.

But it should be noted that being completely honest all the time is impossible. Just imagine really saying what you really think in all situations: movies have been made about that scenario. 

This is an especially important lesson for children: kids have to learn that lying is both bad and also a part of how to engage in an interconnected society. 

"Teaching children about the intentions behind the lies is important so that they can judge for themselves," explained Talwar, "and although we don't like lying, we do tend to evaluate lies that we perceive the person trying to a good thing [...] as being generally less negative." 

So whether something is a 'good lie' or 'bad lie' depends on perception. You have to trust that people tell the truth but also that, if they lie, they have the best of intentions to do so.

I'm not sure if last night's presidential debate was full of good lies or bad lies, but at least now we understand why the candidates are so compelled to manipulate the truth as needed. They're both human after all!