What you 'like' on Facebook gives away your personality

You are what you like!

Be careful what you "like" on Facebook. You're opening a small window on your soul.

A machine-learning algorithm can now predict human personality types using nothing but what people like on the Facebook social media site. A team at Stanford University in California and the University of Cambridge used data from a questionnaire filled out by 86,000 people that identified their "big five" personality traits. The results were correlated with their Facebook activity.

On the basis of between 100 and 150 Facebook likes, the team's algorithm could determine someone's personality more accurately than could their friends and family, and nearly as well as their spouse.

"In the past, my research has looked at how accurately people can judge each other's personalities," says Youyou Wu at Cambridge, one of the study's authors. "It's surprising that computers can do better using just one piece of information – likes."

In 2013, the same group found that Facebook likes can predict private personal information like sexuality.

Shallow assessment

David Funder of the University of California, Riverside, says predicting a big-five score is impressive, but it is just one component of personality. "This is a very broad way of describing human personality. It's useful, but not intimate," he says. "It doesn't really comprise understanding on any deep level."

Funder's own work studying human personality uses more than 100 dimensions, not five. He points out those humans have depths that the algorithms of Wu and Michal Kosinski – Wu's co-author at Stanford – do not scratch. A spouse of 10 years will know their partner in ways that computers are still far from fathoming.

However, Kosinski and Wu's computational approach to understanding personality could be useful in hiring, health and education, where short personality tests are already used.

Their techniques aren't confined to Facebook, so any pot of data that you generate – websites you visit, phone calls you make, presents you buy – could be aggregated and analyzed to figure out exactly who you are.

Work comes to you

Your suitability for a job is one of the first problems that could be tackled. Instead of people seeking and applying for specific jobs, hiring AI's would roam pools of data, seeking the right candidate for a specific task, says Kosinski. "Instead of having an 18th century way of recruiting people, where you plead with the mill for work, the work comes to you," he says. "This is the revolution."

Ideally, every person would have full control of their own data and over which companies and organizations can ask questions about them. But Kosinski acknowledges that the algorithm could be used in an invasive way too, with such personal data available to paying customers. "There's a very big dark side to the technology," he says.

"With one click of the button it could be applied to the entire population of the world. We have to make sure that, in terms of policy and technology, we solve those issues properly," Kosinski says.

Zoologger: Spider has sex, then chews off own genitals

Male South-East Asian coin spider on the back of a female

Zoo logger is our weekly column highlighting extraordinary animals – and occasionally other organisms – from around the world.

Species: Herennia multipuncta (South-East Asian coin spider)

Habitat: Tree trunks and walls across tropical South-East Asia

Sex for the male coin spider resembles war more than love.

First it must mate successfully with a female four times its size that would prefer to eat it than have its babies. Then, the male must do everything possible to keep eager rivals away from the impregnated female. In the macabre world of spider sex, this means self-emasculation.

That's right: coin spiders voluntarily bite off their own genitals. This habit, practiced by around 30 spider species, is not the most obvious way to improve sexual performance. But according to Matjaž Kuntner from the Slovenian Academy of Sciences and Arts, eunuchs have an advantage over their intact neighbors.

For one thing, coin spiders only produce enough sperm for a single sexual adventure in their lifetime. So getting rid of the extra baggage - the two sperm-transferring organs known as palps, which can make up around a tenth of their bodyweight – after one use makes them leaner, meaner and better suited to holding off the advances of competing males.

Keeping other males away after mating with a female is particularly important for spiders as several males can fertilize the same batch of eggs. Only by sticking like glue to its mate can a male guarantee that the next generation will carry its genes.

Extreme monogamy

"It is an extreme form of monogamy. Males put all their eggs in one basket and focus on a single female," Kuntner says.

That is what Kuntner suspected, at any rate. He has previously showed with his collaborators that another species of spider that breaks off its genitals during mating – rather than biting them off afterwards - does it to become a more effective bodyguard. So Kuntner and his team set out to discover if this even more destructive behavior could have similar benefits.

Individual males were given seven days to mate with a female. The researchers then compared the behavior of eunuchs with spiders that had never mated.

They found that spiders that were lacking one or both sperm organs after mating were far feistier than the rival males. The loss of their genitals seemed to give them an extra boost - an arachnid double espresso, if you will.

The eunuchs remained around 50 per cent closer to females and attacked rivals much more aggressively than their virgin competitors. They also stayed active for around 40 per cent longer compared with non-maters when harassed by a researcher's paintbrush, presumably because they did not have large palps weighing them down. Self-emasculation, it would appear, produces better bodyguards.

Eunuch aggression

Kuntner could not discount the possibility that the act of copulation itself was responsible for giving the spiders a boost – virgin males have little reason to want to protect the female. But he thinks that self-emasculation almost certainly increases the spider's motivation and aggression. When they only have one chance, they will do whatever it takes to stay ahead.

For the female, this possessive behavior is actually against her interests, as having multiple mates allows for more varied offspring – which in turn increases the chances of the female's genes being passed on down generations. But then, she does try to eat the male, so a lasting relationship is hardly the first thing on either spider's mind.

Kuntner thinks that this very real danger of becoming lunch rather than lover was directly responsible for the evolution of self-emasculation. Coin spiders are much better off minimizing their sexual encounters with hungry females, and so a one-off mating strategy becomes the most successful option.

This adaptation in turn drove the limited sperm production and the self-emasculating behavior - although which of these traits came first is a chicken-and-egg question.