How has the evolution of human beings been affected by evolutionary forces?

The question is too broad. Every single little facet of our physiology, anatomy, overall morphology, behaviour and our genes has been shaped and reshaped by genetic drift, natural selection, sexual selection over the past three billion years. Mankind has been working on an understanding of these factors and this history for 150 years, and we're nowhere near having a complete picture of even the single clade of hominids, let alone everything in else in our ancestry. How did we lose our hair? How did we lose our tails? How did we develop bipedality? How did we get such big brains? We know that all these things happened, and we know when they happened, and we have plenty of really fine hypotheses for how they happened - but no definitive explanations.

So I'd advise you to do one of two things:

- Ask a more specific question, or

- Just make something up: your guess is as good as mine.