Very few would invest, promote or create without reward. Nobody would go out of their way to help others if they felt neglected and was doing someone elses work for them or doing work that was more difficult to do.
Human nature is, to a very great extent, a product of our mode of production at a given historical juncture. What was considered 'human nature' in, say,1800 AD was very different from what was considered 'human nature' in, say, 1200 AD. Human nature is not simply given to us by a higher power; it is shaped and formed in the crucible of history, and to a certain extent we are even free to choose what is or isn't regarded as 'human nature'. Is it 'natural' to lend money at interest? People in 1200 AD would have said 'no', whereas people in 1800 AD would have said 'yes'. Which of them was correct? You are forgetting the extent to which human beings are shaped by their social environment. People are indeed the way you describe above, but do we have capitalism because people in our society are like that, or are people in our society like that because we have capitalism? If you travel to, say, Latin America or the Caribbean, you will find people have very different expectations of each other and treat each other very differently than they do in the UK or the USA. Just as capitalism has created a 'new man' in its heartlands, so communism will create a 'new man' in its societies. This will be an entirely natural process and need not be imposed. The idea that human beings are capable of helping each other without being motivated by direct material reward is an incontrovertible fact - we can see such people and such societies right now outside the capitalist heartlands. Living as we do in the belly of the beast, we cannot see just how alienated and abject we truly are.