When it comes to sheer friendliness, few humans can match the average dog. But people with Williams syndrome may come close, their unusual genetics granting them a puppyish zeal for social interaction. Now, scientists have found that extreme friendliness in both species may share common genetic roots. A friendly condition Williams syndrome, also known as Williams-Beuren syndrome, occurs when people are missing of a chunk of DNA containing about 27 genes. The syndrome affects about one in 10,000 people, and it is associated with a suite of mental and physical traits, including bubbly, extroverted personalities, a broad forehead, full cheeks,...