Why Amazonian men willingly father children who are not biologically theirs

The Amazon is known for tribes where patriarchal systems weren't very popular.

There was nothing like paternity fraud in ancient Amazonian tribes if your wife had children for other men.
According to research, nearly 70% of the tribes in the old Amazon rainforest practised multiple paternity, where all a woman's sexual partners served as the biological fathers of her offspring.

According to Amazonian tribes, in order for a woman to become pregnant, she must have sex with different men, and the child would inherit the traits of all the men.

These men's seeds will combine in the mother's womb to give birth to a single child. Because these men had multiple fathers when they were growing up, jealousy is not a concern when married women take romantic partners while pregnant.

Anthropologist Robert Walker stated that open relationships were socially expected and tolerated and that men served as father figures for the offspring of all partners.

A man was the principal father of a woman's children if she married him (even if all her children weren't his); all other men were regarded as important secondary fathers.

Why does this happen?

Children in the Amazon had more than one parent who gave them support emotionally and financially. This method was a solution to a society where war and community clashes were common. Other men would serve as father figures if a child's biological father passed away, reducing the load on the widowed mother.

The sharing of wives, frequently within a family, was one of the best methods for two men to forge an alliance. This arrangement was advantageous to men because it drew them closer together and built stronger relationships between the two of them.