David Livingstone Smith, author of The Most Dangerous Animal, believes that a propensity for war has been placed into us by evolution. When resources become scarce, the stronger clan/tribe/nation will win the ensuing conflict, obtaining food, mates and other resources, and reducing the overall population in the region. This rewards those who go to war first. He describes many other benefits of conflict, all of which fit nicely into the framework of evolution.
Face it: war is here to stay.
For the atheist, any higher purpose in life can only come from nature, since we are merely its byproduct. (Of course, we can make up our own purpose and meaning for life, but such ideas do not transcend us.) So let us consider the only transcendent purpose we could possibly have, namely that which nature has handed us: We are intended to be fundamentally self-interested. This is a direct result of the process of evolution which created us. The most aggressive among us eventually win. And, as with the other animals on the planet, we tend to breed up to the limits of our resources. (Some cultures have brought their growth under control, such as native Europeans. The only problem is that other cultures [such as the Arab culture in Europe's case, or the Mexican culture in our case] immediately enter in, and begin to outbreed their hosts.)
As evolution teaches us, the fecund inherit the earth!
In a Star Trek episode (TNG), Geordi and Data are discussing their relationship. Data struggles for a way to describe it, shying away from using the word "friendship," (since he is a mere android). He finally summarizes it by saying, "My neural pathways have become accustomed to you." This is seen as another step that Data is taking in becoming more human. But this actually says more about the postmodern definition of friendship than it does about characters in a science-fiction TV series. For the philosophical materialist, this is all friendship is! There is nothing transcendent about any human relationship! It is merely the accustoming of one person's brain to the presence of another person.