Thanks. So which is a more "tighter" grouping in your opinion?
As far as I'm aware, clades can be as 'tight' as you want: I suppose my parents, my siblings, and me could be classed as a clade, if anyone had reason to do so.
Clades and Linneaen classification are sometimes at odds, we could not class '
reptiles' as a clade, since it does not include all the descendants: it excludes birds and mammals.
quote:
By the 21st century, most vertebrate paleontologists had adopted phylogenetic taxonomy, in which all groups are defined in such a way as to be monophyletic; that is, groups include all descendants of a particular ancestor. The reptiles as historically defined would be paraphyletic, since they exclude both birds and mammals, although these also evolved from the original reptiles.
Colin Tudge wrote:
quote:
Mammals are a clade, and therefore the cladists are happy to acknowledge the traditional taxon Mammalia; and birds, too, are a clade, universally ascribed to the formal taxon Aves. Mammalia and Aves are, in fact, subclades within the grand clade of the Amniota. But the traditional class Reptilia is not a clade. It is just a section of the clade Amniota: the section that is left after the Mammalia and Aves have been hived off. It cannot be defined by synapomorphies, as is the proper way. It is instead defined by a combination of the features it has and the features it lacks: reptiles are the amniotes that lack fur or feathers. At best, the cladists suggest, we could say that the traditional Reptilia are 'non-avian, non-mammalian amniotes'.
Cladistics seems easier to navigate but not as "classified" as (taxon?)taxonomy is.
'Clade' has a particular meaning whereas 'family', 'kingdom' etc, in the Linnaean system are somewhat subjective. Nevertheless, the old system managed to identify
many clades.
quote:
The idea of a "clade" did not exist in pre-Darwinian Linnaean taxonomy, which was based by necessity only on internal or external morphological similarities between organisms — although as it happens, many of the better known animal groups in Linnaeus' original Systema Naturae (notably among the vertebrate groups) do represent clades.
This is actually evidence of evolution. That one doesn't need to believe evolution in order to construct what is essentially a family tree construct regarding life on earth and for it to agree with other methods of constructing family trees (eg., DNA comparisons).
And this is why it is difficult to talk about 'novel' features evolving. Most truly novel features, evolved in very early life. After than, much evolution has been modification of existing features for novel uses. Jaws becoming ear structures, arms becoming wings that sort of thing. Descent with modification makes it difficult to point to an organism and declare 'There is a novel trait!'. Any truly novel trait will likely be small or lethal. In large or complex organisms it is difficult to detect small novel traits like this.
If you were trying to break the species down to the finest details which would you choose? Or can it be a combination of the two systems? A new system so to speak using the two together?
I'm guessing that some of this depends on the species in question and your motivations for 'breaking it down'. For instance, (and I'm just thinking off the top of my head here, so this might not be right) if you were examining a deme (basically: an isolated subset population of a species that breeds only within itself), you might not want to speak of clades since the deme might not be a clade. Though I suppose there may well be clades within the deme.
I don't think I can imagine a combination of two classification systems not creating more problems than it attempts to solve. I'd say your best bet is to use the system that suits your purposes. In evolutionary biology, this is often going to be clades, I'd wager.
Edited by Modulous, : No reason given.
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