> If you make the assumption that each "branching" of the phylogenetic
> tree corresponds to a variation of some base type, then you could
> classify how "evolved" how two organisms were by the number of
> branchings from the root of the tree to the organism in question. Ie:
> primitive organisms are pretty much the same now as they were millions
> of years ago, more advanced organisms have undergone more changes
> corresponding to more branches.
>
> Sounds easy and probably has been done before many times.

Maybe not so easy as it sounds.  Though we know with near certainty that the
organism at the root of the tree of life was a prokaryote, it is a common
misconception that "primitive organisms" (i.e. modern bacteria) are pretty
much the same now as they were way back then.  They have been evolving for
the exact same amount of time as we have; it's wrong to say any one organism
is any further along or any older than another.

> With this concept in mind what is the most advanced "in terms of
> number of branches" organism known and where do humans come in
> comparison.

So despite some flawed basic assumptions, you can ask a sensical question
about how much any modern species has changed with respect to the common
ancestor on the tree of life.  At least in theory we could do this using DNA
base pair changes for a good first order approximation, but because of the
enormous timescale involved and the relatively limited compendium of genetic
data available to us, evolutionary signal gets drowned out by noise much,
much too quickly to make this a tractable thing.

Furthermore, you don't want to confuse what is commonly thought of as
"complexity" with total # of genetic changes during evolution.  Complexity
is our label for a particular set of solutions to historical selective
pressures, and by no means do these represent optimal solutions.  For
example, even though we have no practical way of knowing absolutely how many
DNA changes have occurred between modern and ancient organisms, you can be
sure that microbes have undergone far, far genetic changes than humans or
any other "complex" eukaryote, and so if you really wanted to stick the
label of "most advanced" on any organism, put your money on a bacterium.

Also on your last question, you might check the Tree of Life project.  Still
evolving, but has a clickable tree that lets you browse through various
branches of the tree, with illustrations and text:
http://tolweb.org/
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