Our genes, containing the recipe for making us, do not care about our feeling. All they care about is replicating themselves. Whether their host is the most depressed anxious, suicidal person out there doesn't matter to the genes as long as they get into the next generation, preferably in great numbers. In a sense we are merely the means to obtaining a goal: replication of our genes.
So why do we have emotions? Why are we not just insensitive robots that do not break down because of something silly such as your dog dying, or too much stress at work? The reason is of course that emotions are adaptive in many important ways, and people who lack emotions evidently do not succeed very well in our society. Fear makes us avoid many dangers; pleasure makes us come back to the things that induced it. Guilt and shames tells us we have not been fair and that we should try to fix it, and so on. In other words, we are not born to be happy. Of course we are not born to be sad either; rather we are born with a spectrum of emotions, all of which are probably important in some ways.
What I want to argue here is that, by learning more about evolution, our ancestry, and which situations are likely to produce different emotions we will be able to form our lives as well as our society in such a way that happiness occurs more often, and sadness not so often. David Buss (see picture) from the University of Texas, have written an interesting article on this topic in which he lists the lessons that research in evolutionary psychology have taught us. For example, Buss argues that our anonymous metropolis society is bound to cause distress and anxiety due to a lack of belonging. You can easily live your entire adult life without really getting to know someone today. Our genes, because they are used to a society containing no more than a hundred or so individuals (read about ancestral environment), may feel distressed in the big cities today. Buss advices us to try to get closer to our extended kin, and to make use of today's technology in order to keep in touch with family as well as friends.
Leda Cosmides and John Tooby, two evolutionary theorists from University of California, Santa Barbara (where I used to go to school), have done some interesting research about the meaning of deep friendships. David Buss writes about this research in his article as well. Without going into any details, it can be said that deep friendships are good for all kinds of reasons (e.g. live longer, less stress, happier etc). Talking about your problems is simply good for you (there is no ambiguity in the research on this point), so go get good friends!
Other examples of advice that Buss gives us in his article include, (1) Educating people about evolved psychological sex differences (I believe that sex differences, without proper understanding, can destroy any relationship), (2) Managing our competitive mechanisms, and (3) Fulfilling your desires and dreams (go do that thing that you have always dreamt about!).
Another thing that makes us happy is democracy. If you ask people whether they are "happy" and "satisfied with life as a whole", and then correlate that with the degree of freedom in the country, you will find a very nice positive correlation (see diagram). In other words, countries with democracy, free elections, and elective rule have happier citizens, than dictatorships. So here is a lesson for the society as a whole, don't vote for dictators, and keep fighting for freedom of speech…
Some people say that a belief in evolution by natural selection will corrupt a person into immorality. In contrast, I think that evolution is one of the keys to create a society in which people are happy, or as my former teacher put it:
"Go save the world, but do it using what you know about human nature"