In Climbing What Does Vs Stand For?

phylogenetic classification summary.

animal biology was revolutionized during the past 30 years by applying the method of Classification Willi Hennig : the cladistic formalized in 1950, which proposes to create groups with a common ancestor and all its descendants. So that the Darwinian concept of descent with modification is for the first time completely and thoroughly exploited. But before returning to the principles of classification back on the approach of the classifier and the target of a relevant classification.

[phylogenetic tree of life proceeds from the cladistic method of Hennig, circular representation.]

Why classify?


To learn how to classify it should clearly define the reason for the classification. So if the record shop class musical genres is the purpose of enabling the amateur to easily find the music he loves. Classify this is not sorted (Separating a set into two groups for example rock / no rock spine / no spine). Sorting allows for determination keys, but not to make combinations, there are no fan of "non-rock '. Rate this order is not (because of stored items in a group as a continuous variable: for example in order of increasing size); imagine Fnac CD with all mixed in alphabetical order. NO, is realizing Sort groups of proximity between different elements. Indeed the interest of a classification is to make intelligible (understandable) diversity of a collection, whether cash or discs.

Willi Hennig (1913-1976)

How to classify?

To classify it must answer the question "who is closer to whom?" This close relationship of species (phylogeny ) is distinguished from relations of descent (genealogy). Indeed it is impossible to answer the question of who goes down, unless there is a civil registry of life dating from 3 Billion years hidden in an Amazon jungle ...

So we will classify the species according to characteristics they share, assuming that the closest species are those that share more common characteristics. Each evolutionary innovation makes it possible to group all species form a monophyletic group said that includes a hypothetical ancestor (the first to introduce this innovation) and all its descendants. In this way, it produces coherent groups in terms of evolution.


The phylogenetic classification

In summary for classifying a sample of species four steps needed: 1 - Identify characters counterparts. 2 - Polarizing the characters with an extra-group, ie determine which characters are ancestral and derived characters. 3 - Place on trees all evolutionary changes. 4-Select the most parsimonious tree, is to say the one with the fewest assumptions transformation.

[Example of tree construction phylogenetic:]

-matrix characters (1: indicates the derived state, 0 the primitive state of nature Trees

possible with this matrix, only the most parsimonious is retained

greater the number of significant cash plus the number of trees to be explored is large, and without this computer cladistic method is not feasible, so that Hennig has formalized the procedure from the 50 years it took another 30 to 40 years for that it is applied, and it will still take some years to see disappear completely the traditional classification called eclectic.

Article Wikipedia

[Home]