https://www.psychologytoday.com/us/blog/the-real-story-risk/201211/the-thing-we-fear-more-death
Early humans survived by their wits and their ability to collaborate. Those that worked together well, helping others in their group, probably survived and passed on traits that contributed to social behavior.
Failure to be a part of the social group, or getting kicked out, probably spelled doom for early humans. Anything that threatens our status in our social group, like the threat of ostracism, feels like a very great risk to us.
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Ostracism appears to occur in all social animals that have been observed in nature,” says Kip Williams, a professor of psychological sciences at Purdue who has studied ostracism.
“To my knowledge, in the animal kingdom, ostracism is not only a form of social death, it also results in death. The animal is unable to protect itself against predators, cannot garner enough food, etc., and usually dies within a short period of time."