From official sources: From the Bible. In the Old Testament (The Book of Wisdom of Jesus, Son of Sirach, Chapter 13, verses 19-20), it is said: “Every animal loves its own kind, and every man loves his neighbor. All flesh is joined to its own kind, and man clings to his own kind.” About people who, willingly or unwillingly, seek out like-minded people, those who are similar to them in some way.
From psychiatry (“but this is inaccurate” meme) – people with reduced intelligence almost always seek support and form a group of their own kind. They need recognition or approval from hospital staff, otherwise their existence is destroyed.