Cooperation is one of the hallmarks of being human. On a regular basis, we all enter into helping others in small but important ways, whether it be letting someone out in traffic or giving a tip for good service.
We do this without any guarantee of payback. Donations are made at a small personal cost but with a bigger benefit to the recipient. This form of cooperation, or donation to others, is called indirect reciprocity and helps human society to thrive.
Group-based behaviour in humans originally evolved to overcome the threat of larger predators. This has led to us having a sophisticated brain with social abilities.
The social brain hypothesis proposes that the large human brain is a consequence of humans evolving in complex social groups where cooperation is a distinctive component.