Multi cellular life has evolved several times. There are several distinct cases of single called organisms promoting conditions which aid others of it's species. Causing a colony to form, and then spawn new colonies.
Now, highly complex multicellular life seems to share common descent. But that likely has more to do with predation than anything else. Further single called organisms preform horizontal gene transfer to both other single called life and multicellular life, making things impossible to trace back.
It's one thing to say there might have been abiogenesis elsewhere that created something like the simple self-reproducing energy machines that bacteria and archaea are. It's another to claim that there is some inevitable progression from that to complex multicellular life. In my opinion this is a very teleological, very 'progressivist' notion of evolution that implies that one inevitably follows from another, and it is not borne out in the reality of what we know so far about happened on earth and what follows from first principles.
There may be a lot of complex, self-reproducing systems in the universe. It's arrogant to assume that any of them have to look anything like what we call "life" unless by life we mean the simplest single cell organisms. [edit: In fact it looks like simple prokaryotes evolved _twice_ on earth a "short" distance in time apart].