In the 1990s, anthropologist Robin Dunbar extrapolated from the size of the primate neocortex that humans can maintain only about 150 stable relationships. “Dunbar's number” became famous. In 2021, Stockholm University researchers reran the analysis with more data and modern methods: their confidence intervals spanned anywhere from 2 to 520 people. Their conclusion: no precise figure can be given. Dunbar disputes their method.
Remembering is not replaying a recording — it is rebuilding. Each time you recall a memory, it becomes temporarily malleable and can be altered before being stored again. That is why two people can sincerely remember the same event… differently.
In 2003, Johnson and Goldstein compared European countries. Where you must tick a box to become a donor, consent rates ranged from 4% to 28%. Where you're a donor by default unless you opt out, they topped 85%. People aren't more generous on one side; most simply stick with whatever option was chosen for them.