a201-11f-10-Phylogenies - Introduction to Biological...

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Introduction to Biological Anthropology: Notes 10 Classification and Phylogeny: Evolutionary family trees Copyright Bruce Owen 2011 - Species of living things have an odd property: - species can be lumped by similarity into groups - those groups can be lumped into larger groups by similarity - and so on, in ever larger, more inclusive groups - in most cases, there is only one way to lump a given lot of species so that they form sets and subsets that are similar - if you gave several careful people the task of lumping species into groups, and those groups into larger groups, they will all come up with pretty much the same scheme - this pattern of nested groupings is the basis of the Linnaean taxonomic system : the system that we use to scientifically name organisms - one or more species are lumped together into each genus , then one or more genera lumped together into each family , one or more families lumped together within each order , etc. - this nested grouping is not an arbitrary creation by biologists - instead, like the existence of species themselves, it seems to be a fact of nature, “out there” for us to observe - To illustrate the same thing in a different way: - Animals can be divided into those that have backbones (vertebrates) and those that do not (invertebrates).
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Intro to Biological Anthro F 2011 / Owen: Classification and Phylogeny p. 2 - Animals with backbones can be divided into those that nurse their young (mammals), and those that do not (reptiles, bony fish, amphibians, etc.). - but the same division does not apply to invertebrates, because there simply are no invertebrates that nurse their young - every single animal that nurses its young has a backbone - Animals that nurse their young (mammals) can be divided into those that have placentas (placental mammals), and those that do not (marsupials and monotremes) - placenta: a structure in certain mammals that connects the bloodstream of the mother to that of the fetus in the womb - again, this division only applies to mammals, because there are no placental animals that do not also nurse their young - The pacental mammals can be divided into numerous groups, and so on - These groupings are not arbitrary, because each subtype is found only in one group - for example, every single placental animal is a mammal - among all the reptiles, fishes, amphibians, etc., there is not a single animal with a true placenta - every single living thing can be fit neatly into this hierarchical system of subgroups nested within subgroups - there are no in-between cases - and there is only one way that all the species can be arranged like this - of course, there is debate about certain cases and details - but the biologists that argue about these cases don’t think they disprove the general pattern, only that a colleague has made an error in his or her observation of it - This may seem obvious, but the fact that species can be classified in this way is actually a very specific, unusual feature of living things
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a201-11f-10-Phylogenies - Introduction to Biological...

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