In his original research, Dr. Dunbar studied monkeys and apes and determined that the size of the neocortex, the part of the brain responsible for conscious thought, correlated with the size of the groups they lived among. The neocortex in humans is even larger, so he extrapolated that their ideal group size was, on average, 150. In the new study, Dr. Lind said he and his team used updated data sets and statistical methods and found that the size of the neocortex did not limit the number of connections people could maintain. Dunbar’s number, he said, “has been criticized for quite a long time.” Dr. Lind’s team found that no maximum number of friendships could be established with any precision. In an interview, Dr. Dunbar, a professor of evolutionary psychology at Oxford University, defended his research. The new analysis, he said, “is bonkers, absolutely bonkers,” adding that the Stockholm University researchers conducted a flawed statistical analysis and misunderstood both the nuances of his analyses and of human connections. “I marvel at their apparent failure to understand relationships.”