Just reading the 2004 paper that introduced the concept of "blue zones" where people live to be extremely old, and:

"An additional and interesting hypothesis is that the high rate of inbreeding determined by frequent marriages between consanguineous individuals and low immigration rates have…facilitated the emergence of genetic characteristics that…might actually protect individuals from diseases that are major causes of mortality…” https://shs.hal.science/halshs-00175541/file/2004%20POULAIN%20BZ%20EXP%20GERONT.pdf