I hear a lot that PhD students are expected, and for the most part, work independently on their research projects. This seems to be reflected by how being a 'first-author' on a paper is highly valued as that implies he or she has done the vast majority of the work.
However, I've found from my own experience that I'm a lot more productive with my ideas if I'm working together with one of my peers on a research project.
So I'm wondering how often does equal collaboration between peers occur. If it does not happen often, why isn't it encouraged more?