how can all companies be employee owned?

Is this rhetorical? I didn't say they could (or couldn't be). If you mean it in a curious way than let's start with 'how can a company...'

How is capitalism different from early human tribes?

It depends on which capitalism you mean, Marx's or Milton Friedman's. Also which tribe. If early human tribes were like modern ones, they had a lot of different ways of doing things.:)

For marx, you could probably stop at "they don't live in cities or work for wages" like they do in capitalist systems.

For Friedman's capitalism, they tribesmens affairs are probably dictated by customs and communal nterests, not private interests.

Idk, though. It's theoretically possible for ancient human culture to be capitalist under Friedman's definition, if their rules are compatible. Under Marx's it doesn't matter what they do, capitalism is an urban-industrial society.