I bet you were already familiar with the notion. Modern âcladisticâ approach to taxonomy simply takes the view that it is almost meaningless to speak of âAll mammals but Matt Taylorâ.
Well⌠meaningless is maybe a strong term, but, say⌠it opens for more insights in the end, to rigorously constrain ourselves to the view that all allowed names should be clades.
Whenever it is still somewhat significant to speak of âAll mammals but Matt Taylorâ, or to refer to historic classifications, weâd speak specifically of âstem groupsâ, or sometimes âevolutionary gradesâ for, eg, all which did not evolve your haircut yet.
Those are simply ways to refer to a non-phylogenetic name, that is, a name which is not a clade.
Remaining allowed cladistic names can still be divided in two categories⌠crown groups (the most often implicit meaning⌠such as when speaking colloquially of âmammalsâ), and total groups. Sometimes same name can be given that terminology explicitly.
Okay maybe the above example could not apply since âAmniotaâ definition seems to benefit from an embedded âcrown groupâ status. But you get the idea.
Somewhere along the line linking the total group to the crown group for Amniota, youâll be lucky to find the real first âamnioteâ in the biological sense, of an animal not requiring water to lay his eggs⌠that got the clade its name in the first place. And that can be a third understanding of a colloquial âamnioteâ term. Tricky, huh ?
When branching into total groups, an acceptable cladistic tree always has to be âbinaryâ. A split group always ought to split into exactly two branches : one group and its so called âsisterâ-group. Although gaps in our knowledge, and debates over where to branch what, often lead to many remaining shady areas where we still refer to stem groups globally, or allow one branch to have further splits, until those concerns are settled. Also, since modern classification is based on computer-aided statistical studies across many many species, and given that the prevailing hypothesis get rearranged quite often⌠it is quite common nowadays to find branches without a name.
Also, I guess modern views on the evolution of genus Homo itself casts some doubts as to whether that classification really ought to be a binary tree (and for that matter, an acyclic graph at all). But if you dezoom somewhat, I think the cladistic view makes sense, still.
Anyway⌠shall we delve into some more details about your ancestry ?
I think paleontology and comparative studies across species have much to tell about brains too