Actually, LUCA is mainstream science, but it's NOT saying that the last ancestor was a bacterium as much as apologists like Mijo would like to pretend it is. Bacteria are species that exist today... they evolved from bacteria like ancestors--as did we...but we wouldn't call those things bacteria as we define bacteria today--because they weren't. As simple as we think of bacteria to be, they've been evolving for a lot longer and a lot more generations than we have.
But pay no attention to Mijo-- he is a creationists and he's doing what DOC is doing but more subtly. He's confusing rather than clarifying and defending creationists and the creationist position as he always does. He readily starts similar threads with silly inferences and ignores all answers to his queries while saying nothing of value on the topic. We have a common microbial ancestor-- we are still trying to figure out the nature of it. We've recently learned that vertebrates (from which our brain arose) and invertebrates have a common worm like ancestor.
http://www.sciencedaily.com/releases/2007/06/070629101101.htm
Now, these were not today's worms--worms too have been evolving for eons-- but we understand that they were what we'd call a worm due to features we use to describe worms.
And all our worm-like ancestors would have been identical for all of us. As would our microbial ancestors-- but they are NOT the microbes we see today-- they are their ancestors of trillions of generations back in time.
Yep. Perhaps I should have qualified my post by saying "even if what you say is true...".
I have yet to meet two evolutionary biologists who agree on the exact nature of the LUCA. Some say a single individual, some say a single type, yet others point to horizontal gene transfer and state that, quite possibly, it was more then one species.
And yes, evolutionary biology is very cool.