Biologist here.

If we were meant to be selfish and lazy and arrogant and greedy, then we wouldn't be forming tribes and packs and groups and villages and towns and cities and governments and militaries and social groups and so on and so on. We wouldn't have survived. We would have been living solitary lives like male lions. Instead, most people naively look at a bacterium eating until it bursts, or a cat hissing at another cat for no apparent reason, or a praying mantis eating another praying mantis that it just copulated with, and we think "oh that's exactly how nature is meant to work, all around, no exceptions". In truth, when you look at most vertebrate animals, we all exhibit varying degrees of cooperativeness, all powered by empathy and fear of social pressure (for when empathy fails). Most of all vertebrates, this is exhibited by mammals. And most of all mammals, you see it in primates. And most of all primates (by very few degrees in some cases by the way), you see it in humans.

Humans specifically evolved to be cooperative. Our cooperative nature is what gave us an edge to survive until the beginning of history. You can find many examples and anthropological evidence, but the simplest one is how Homo sapiens (more cooperative and able to maintain bigger groups) managed to out-survive the Neanderthals (less cooperative and spread into much smaller groups).

You can observe it in our physiology. Our brains have an extremely developed system of empathetic neurons. We feel the plight of others, and our natural instinct is to help them. This would be a pretty big disadvantage if the idea is that selfishness wins the day. You can see this in action very clearly in children of all ages:

• When one baby cries, all other babies in the room start crying too. If one is in danger, perhaps we are all in danger. Let's cry together to save ourselves.

• When a child's toy breaks, often another child will come along and offer them another toy (free of charge too). We don't want to see others be sad, because that makes us sad.

• If you ask a child "Would you prefer that you get ice cream, but your brother doesn't, or would you prefer that both of you get ice cream?" They'll almost always answer "Both". Even if we don't stand to lose anything, we don't want to make decisions that make others suffer unnecessarily.

• If a teacher asks a teenager to tell on another teenager about some minor transgression, they'll almost always refuse, even if they don't like the other person. Mutual support is ingrained in us. We don't want to let down other members of our group, because group cohesion is more important than individual success. Even in the most selfish sense, we instinctively fear that the rest of the group will shun us for bringing harm to one of our own.

You can also see it in adults even. Every time there's a disaster in some far corner of the world, and the calls come for help, along with the videos and posts showing the desperation and fear, then total strangers suddenly rush to embrace the victims across the internet by volunteering, sending aid, messages of support, or even the mere act of checking up again to see how things turned out.

What happens rather is that we have built a system that systematically dismantles our cooperative instincts in favour of individualism. This is one reason we all feel unhappy at such high rates. Every time we see a beggar on the street and turn the other way, every time we hear of someone else's problems and we choose to ignore it, every time we come at a crossroads where we choose between our careers and the well-being of ourselves and others around us, every single time we go into battle against our nature and we kill a bit of ourselves. And then we convince ourselves that the mutilated and unrecognized carcass that our psyche has become, that that abomination is how we always were and how all humans are. It makes it just a bit more bearable to live with ourselves.

Take away this system, and suddenly you can raise new generations that act perfectly well according to the human nature that brought us all the way to here. Again, this is easily observable. Travel in less developed countries away from the centers of capitalism, and see how people in a community behave to each other. Not just day-to-day politeness, but actually how their system is set up around cooperation and mutual aid. Upbringing is a key we constantly ignore when we discuss this "human nature".

For rich people, the effects of this psychic self-mutilation are even worse. The upper classes convince themselves that they are somehow better than everybody else. That they are almost an entirely different species. That those who toil under them don't deserve anything better. That the rich are rich because they are the smartest, bestest, gentlest, humanest humans to be around. And then they raise their children to believe this shit from birth. And then they raise their children, and so on. The result is that one way or the other, the rich and powerful separate themselves from the rest of the group. They make their own group. And then they see how small their group is, and how big our group is, and they start getting paranoid on what we will do to them for abusing us. Actually they are not afraid because they are abusing us. They are afraid because they see us the way they see the rest of the world. They are selfish, greedy and moralless and so they think we are too. They think we are out to get them and steal their stuff, the same way they operate. Which gives them even more reason to abuse us, suppress us and lie to us about a variety of stuff like "it is our god-given right to amass this much wealth" or "it's human nature". And that is exactly when societies break down.

Initially, Ancient Rome had a vast area around the city designated as public land. This land didn't just belong to the state, it belonged to everyone. This was really good arable land too. So every family in Rome, be it patrician, plebeian or proletarian was given a certain lot from this land to farm and work as they see fit in order to support their family. Furthermore, another big portion of this land was kept owner-less and was tended by slaves (unfortunately) and paid labourers to produce food which was allotted to the entire population of the city. This land could actually produce enough food to feed about 200 000 people every year. Extremely big and extremely fertile land. And no family could own more than a tiny fraction of this land.

So for around 500 years this set-up was maintained, until some patrician decided to run a scheme where they'd use the names of dead soldiers to allot plots of public land to their "miraculously alive" persons, and through them he would own the land. He then wanted to acquire even more land by using gangs of thugs to convince other families to sell rights of work on their lots to other fictitious personas he created. Pretty soon all the other patricians followed suit (for fear of missing out). About 50 years later (150 BC) most of this land was in the hands of the patricians and everybody knew it. Efforts to reverse this land theft were met with brutal repression (Michael Parenti covers this in his book on Julius Caesar if you are interested). We are talking actual death squads roaming free through the city and killing thousands within a few days. Eventually this is what led to the dissolution of the Western Roman Empire about 300 years later. It wasn't the inherent greed of all Romans that did this (EDIT: Actually the vast majority of Romans, including some of the aristocrats were constantly banding together to fight this; you know... cooperating). It was rather the greed of a select few individuals, who had set up a system where they had all the power and all the means to act upon this greed.

Your friend sounds like a very bad biologist to me. Probably a biochemist :P