Read: A short history of empathy

Besides their gregariousness, people with Williams syndrome have a distinctive physical appearance, with delicate features such as a small, upturned nose and a pointed chin. And the condition often comes with a constellation of challenges and health risks, including learning difficulties, poor movement coordination, digestive issues, and life-threatening cardiovascular illness.

Ben has already undergone multiple surgeries as a result of his Williams syndrome, though he tends to downplay his discomfort. “He’s been through so much,” says Terry, who is also a spokesperson for the WSA. “But he just doesn’t go there, you know? His spirit is all about the good stuff.”

Scientists have had a tough time explaining all the diverse symptoms and characteristics associated with Williams syndrome. Recently, however, great strides have been made in understanding the condition’s origins, including the reasons that people with Williams syndrome are so sociable. In an unexpected twist, some evolutionary biologists believe this research could even shed light on the mysterious roots of human altruism.

Cardiologists first identified the basic attributes of Williams syndrome in the 1960s, but it was only in the 1990s that scientists managed to pinpoint the condition’s genetic basis. People with Williams syndrome lack 26 to 28 neighboring genes on the seventh human chromosome. This region includes various genes with diverse functions, from regulating immune function to controlling organ growth and development. One gene codes for a highly flexible protein that is essential for many bodily tissues. A deficit in this protein thickens the artery walls with muscle, leading to lifelong cardiovascular problems.

The loss of another gene, BAZ1B, impairs the migration and survival of what are known as “neural-crest cells” across the body. In an embryo’s early development, these cells usually gather at the head and then move across the body, where they form the basis for many tissues—including the bones and cartilage in the face, the teeth, and the eyes, as well as the heart and the digestive system. A disruption of this process leads to Williams syndrome’s markedly different facial features.

Neural-crest cells also form the adrenal glands, which shape our hormonal responses to stressful events. Some scientists have argued that the reduced migration of neural-crest cells could contribute to reduced fear and aggression—potentially leading to increased social behavior. That would certainly fit with the experiences of many people with Williams syndrome, who find it harder than the average child to comprehend “stranger danger.” “When I was younger, it was hard, because I wanted to go up to every single person and say hi, and I wanted them to be my friend,” Maegen Miller, a 30-year-old woman with Williams syndrome, told me. This theory tallies with various measures of social behavior, which show that people with Williams syndrome tend to be less sensitive to others’ negative emotions and signs of hostility, so that literally everyone can seem approachable.

Ultimately, though, such characteristics probably arise through many different mechanisms. Most people with Williams syndrome are also missing a gene called GTF2I, which contributes to the production of myelin, the fatty sheaths that normally surround our brains’ neural connections. The loss of myelin likely impairs the transmission of electrical signals across the brain, which could help explain some of the cognitive difficulties and the lack of motor coordination associated with the condition.