>selfishness occurs in higher frequency and intensity

Maybe because that's an adaptation to current environment. As an example, propaganda is a mechanism to induce colective beliefs of the current state of something, the country, the world, etc. There are lots of data showing that some crucial social agreements that allowed the socio economic boom of the 60's untill the 90's are now outdated by the political decisions to cut economic balancing measures, starting in the 70's. That's one the reasons we believe in scarcity, violence, etc. Because those stats are regressing. You can also as an example easily see the differences between movies and series in the 1980's and 2010's regarding those themes. And the evolution in media consumption. And the advantages for polarized speech in politics in order to preserve power. Etc. This ends up becoming part of the current culture.

>The existence of mostly selfish billionaires disproves your point

I was expecting this to come up. It's not as you said: they do not have stability and peace, not inside. Most of them only have material peace, and it's frequently argued that the need to accumulate wealth is a way to compensate the lack of other things.

>In modern consumption driven society, selfishness will be more valuable.

This is of course very questionable and debatable.

>scientifically test human nature in an accurate manner

Observing babies has been tried. Of course there's lots of limitations there. What we can say is, then, that it is quite "irresponsible" to jump into conclusions regarding what "human nature" is or is not. Maybe we can just keep doing something very human: observe.