There's no real evolutionary explanation for being kind to one another. However, it's a value that most people would agree (to a certain extent) they share. But what's the point? Why be nice simply for the sake of being nice? You can give me the reasons why being nice and treating others with respect and dignity are better for the world as a whole, but that doesn't explain the point or purpose for such a value when it seems counter-productive to a system based on survival of the fittest. Of course we are products of our small social structures and on a larger scale you can see how certain people groups certainly are not "nice" to other people groups. This has been a habitual cycle throughout history...but for the most part there is an intrinsic pull in each of us to "be nice" and I don't understand how evolution explains this mess.
C.S. Lewis made the following statement in his book, Mere Christianity, and I think it is helpful in this discussion.
‘Niceness’ -- wholesome integrated personality -- is an excellent thing. We must try by every medical, educational, economic, and political means in our power to produce a world where as many people as possible grow up ‘nice’; just as we must try to produce a world where all have plenty to eat. But we must not suppose that even if we succeeded in making everyone nice we should have saved their souls. A world of nice people, content in their own niceness, looking no further, turned away from God, would be just as desperately in need of salvation as a miserable world--and might even be more difficult to save.Lewis understood, with a great deal of conviction, the excellence of the human quality of "being nice" and as he stated this value is something that individuals, cultures, societies and people groups should invest limitless resources into promoting...for everyone. But the value of being nice is not an end in itself, if you're looking at things from a Christian worldview. As he stated, we must not assume that when we have succeeded in making everyone nice that we have somehow redeemed people in any eternal sense of the word. What we have done is simply made people 'better' in a temporal way. No doubt, people being kind to each other would make for a much better world than the one we live in today, but curing selfishness does not mend a sinful heart and in fact (as Lewis pointed out) can actually cause a greater harm in an eternal sense. To say it a bit differently, as we try to promote morality throughout humanity, its possible that at the same time we are doing the world a disservice by pointing them to the value of being nice as the end in itself.
Very rarely do good people reflect on their goodness as a way to see the wickedness of their sin or the true condition of their heart. There is one essential need that all humans have and that is the need for salvation from their own sinful choices. God demands perfection and nobody (regardless how nice they are) is capable of living a life free from any kind of evil or sin. When people do bad things or when you turn on the 5 o'clock news to discover another despicable act of selfishness, pride, depravity, or violence...avoid the basic human reaction to simply say if only people could just be nicer to each other this world would be a better place. Yes, being nice is a wonderful quality; one which we should all be striving for, but in the ultimate sense...nobody was restored into a right relationship with Christ for being a nice person.
Only when we turn towards Christ and his substitutionary atonement on the cross in our place can we understand the root issue which is causing evil in this world. Sin is the root of all human acts of evil and sin has an ability to manifest itself in numerous ways. By taking away the tangible evidence of this very real and eternally-fatal heart issue, we do nothing to help a person see their need for Christ and purpose or point of his work on the cross. We take away a very basic tool to help people understand the true condition of their hearts and their need to repent for their sin and accept Christ's perfect sacrifice and his infinite grace as their means to being restored into a right relationship with God...which is the true and only end for all things.
By all means, be nice...but don't be nice simply for the sake of being nice. Be nice, because your life has been transformed by the gospel of Jesus Christ...and now you live to glorify God in all the things you do.
For His Glory,