Saturated in pink and sparkles, the Barbie movie is full of ribbons and hearts, gingham and polka dots: a universe of cuteness. And yet, according to the internet at least, the most adorable thing in the film is not the eponymous heroine but her consort, Ken. Margot Robbie’s Barbie may be glamorous, but Ryan Gosling’s Ken is cute – quite an accomplishment for a man-baby intent on imposing patriarchy on Barbie Land. Scientists have been studying the nature of cuteness for decades. It’s now widely accepted that we are hardwired to both look and act cute when we’re very young and to respond to cuteness ourselves. When kids are cute, women and men alike pay attention to them and care for them, which not only helps children to survive but also to learn how to communicate and cooperate. That’s why characteristics that make something cute tend towards the baby-like. Our cuteness detector is generally set off by a big, round head with large, low-set eyes, chubby cheeks and limbs, plus an awkward, tottering gait. Brain scans show that objects with these qualities immediately capture our attention, even before conscious thought occurs. Cute things activate the pleasure centres of our brains and prepare us to act with empathy and compassion. Studies have shown that people are more likely to fill out a survey, sign a petition or offer to help others when the request is accompanied by a puppy or even a cute picture. Cute qualities are great for triggering consumption as well as care, which explains why so many consumer products are designed to piggyback on our responses. Some of these, like ones in the Hello Kitty range, achieve maximum cuteness with minimal features. Drawn without a mouth, the character emulates the blank look of a child who has yet to understand the world. Other aspects of cute culture are, by contrast, way over the top. In Barbie Land, soothing pastel colours are highly saturated to make them pop, and round, comforting shapes abound. Cars are too small; toothbrushes are too big. Waffles and conference tables are heart-shaped, details that overload the audience with cuteness. Which brings us back to Gosling’s Ken. Though he lacks the obvious visual features that scientists have identified as cute, his behaviour is appealingly childlike. He dons a fluffy fur coat in a vain attempt to wield authority. Through all his wannabe bad-boy behaviour he beams goodwill and vulnerability. Furthermore, his immaturity signals the potential to change. To his fans he’s cute because of his flaws, not in spite of them. The question of how to trigger the cuteness response has implications beyond toys and movies. Though childlike behaviour can be appealing, it’s difficult to get it right in the real world. For example, one AI chatbot named Pi is designed to project a warm persona and to show curiosity and enthusiasm. However, with responses peppered with emojis and bland expressions, Pi can be cloying rather than cute. It’s a fine line, and people’s levels of tolerance vary. “Are you too cute?” I asked Pi, only for the chatbot to thank me for the compliment. Though striking a balance between cute and cutesy is difficult, developers in the fields of AI and robotics will no doubt keep trying. Adding cuteness can bridge “the uncanny valley” – that sense of creepiness induced by not-quite-human replicas. We’re more likely to indulge cute entities and forgive their “childlike” mistakes. So don’t be surprised if new robotic or artificial personas use cuteness to solicit our affection. There is a new take on why we find cuteness so hard to resist, which may help explain some of Ken’s appeal. Many scientists support the theory that females at the dawn of human evolution may have preferred kinder, gentler males who would help take care of children. In other words, Homo sapiens emerged because women preferred men who exhibited this kind of adult cuteness. The preference might even have caused us to become the first self-domesticated species. When animals are domesticated, they become cute as well as tame, retaining more juvenile features in adulthood. For a long time, it was assumed that this “domestication syndrome” was a result of selective breeding. But, initially at least, we didn’t breed animals to stay young-looking – we bred them to be friendlier. Why do these traits emerge? The answer may lie in the neural crest, a structure that plays an important role in developing embryos. Cells migrate from the neural crest to many areas of the body, but they are inhibited in less fearful and aggressive individuals. Selecting for this inhibition has knock-on effects, which lead to the other features of domestication syndrome, from curly tails and floppy ears to shorter snouts and smaller jaws. While humans don’t have floppy ears or tails, we have smaller, rounder skulls and reduced brow ridges compared with other early hominins. Simply put, we’re cuter than Neanderthals. Are we also tamer than they were? Violence and sexism are still endemic to our species, but overall we are less aggressive and patriarchal than chimpanzees, our closest living relatives. Aeons ago, did women prefer cute, sociable Kens to belligerent cavemen? Over time, such choices may have bent the arc of our evolution away from our ape-like ancestors and made us who we are. Joshua Paul Dale is a professor at Chuo University, Tokyo. His book Irresistible: How Cuteness Wired Our Brains and Conquered the World will be published by Profile on 9 November. To support the Guardian and the Observer buy a copy at guardianbookshop.com. Delivery charges may apply. Further reading The Power of Cute by Simon May (Princeton, £12.99) Survival of the Friendliest by Brian Hare and Vanessa Woods (Oneworld, £10.99) Kawaii!: Japan’s Culture of Cute by Manami Okazaki and Geoff Johnson (Prestel, £19.99)