What reasons did early humans have to join together into groups instead of stay independent

In short: better protection.

Especially in the early days, humans were at danger of being eaten by many predators, and being in bigger groups gave them a better protection (a single human has no chance with a lion, but a single lion has no chance against an organised group of humans!)

Also, in groups they could hunt better.

White dwarf is very hot, but also very small and that is why it may appear dim.

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