Socialism can only work of everyone in society ignores basic human nature and millions of years of evolutionary biology that have ingrained the need to be selfish for survival into our genes. Our survival is now longer predicated on that level of selfishness, but you're not going to reverse the wiring in our brains that reward it.
I agree with the point that evolutionary biology has rewarded a degree of selfishness, and that natural selection has embedded it in our natures. But I would argue that our evolutionary history has in general only rewarded mild degrees of selfishness, and that higher levels of selfishness have been counterproductive to an individual's survival and ability to pass on their genes. We have evolved as social animals, living in tribal groups of somewhere of the order of 100 people. Arguably much of our intelligence has evolved through the need to build and maintain a complex web of inter-personal bonds, knowing who to trust and who not to, and establishing reciprocal altruism. We can argue convincingly that for a species of solitary creature, selfishness will certainly be selected for, and selflessness will not. I think we are on less solid ground arguing the same for social animals.
Beyond this... I'm not in favour of outright communist-style absolute equality of outcome, I'm more in favour of democratic socialism, a capitalism-lite where truly progressive taxation of both income and wealth work to remove some of the most egregious excesses, and government intervention works for the benefit of the whole population, and removes all innate privilege. This may be a dream that is unlikely to see reality.
I would say that most modern national governments do exhibit extremely selfish tendencies, but I think this is not because all or most people are extremely selfish, but rather that the sort of people who seek power tend to be more selfish than those who do not. If instead we base our assessment of human nature not on politicians, but on volunteers and charity workers, and for example the employees of
MSF, who could work extremely well-paid jobs in private healthcare, but instead choose to risk their lives in war zones in the most troubled parts of the world... if we base our assessment on these people, then I would say humans don't seem particularly selfish at all.