Explain the existence of generalized reciprocity

For thousands of years, humans have related to each other through ties of reciprocity (exchange of things or favors for mutual benefit). The textbook describes two main kinds of reciprocity: generalized reciprocity and balanced reciprocity. Describe them and the social situations in which they are likely to be practiced. At first glance, generalized reciprocity may seem like irrational behavior. However, the textbook provides logical reasons to explain the existence of generalized reciprocity. Describe these reasons. Do you find them convincing? Why? Or why not?