The main purpose of Homo sapiens (modern human) is to serve in evolution. Every single individual whether big or small, physically strong or weak, sustainable or unsustainable; their main purpose is to evolve. If it is weak then their goal is to evolve stronger and if stronger, their goal is to evolve more stronger.
Biologically speaking, evolution is not based on similarities; it is based on differences. If all humans are same, then we are not serving towards evolution. Thus we are aware that is not happening. This follows that every human are different and that is why we are evolving.
The theory of evolution is based on the idea that all the species are related and gradually change over time. Lamarckism and Darwinism all explains that this what drives the evolution.