Why are we good?

I feel that there are three main reasons why humans are willing to do good to others. They are as follows:

Altruism
A mother would protect her child in exchange for her life. This fact is believed by most people, but thinking about it, this seriously contradicts Darwin's theory of evolution of the survival of the fittest. Why is this so? I feel that this is because among someone's blood relatives, especially among his immediate family, there is this bond that brings them together, because they share a common ancestor, like a grandfather. They can be considered under the same 'group', and since they share similarities, they would want to protect their own kind, and thus this selflessness comes into play, where someone would sacrifice anything to do something good for another one who is his blood relative.

Reciprocity
Whenever someone does something good to someone else, that person would have a sense of gratitude towards his benefactor, and thus would want to repay him for the good deed. This follows the principle of 'you sratch my back, I sratch yours'.

Personal benefit
Many people aim to get the best for themselves, and would do anything to get that, including being good to other people. For example, offering someone a bribe could be considered as doing something good to him, where the aim of the bribe is to get that person to give something back, for personal benefit. In a world where the fittest survive, such tactics have to be employed when dealing with other people, and in other words, we do good to other people to be good to ourselves.