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Modern Classification. 17.2. What is a species. It used to be thought that anything that looked different were considered to be different species. We now know that any given species has variation .
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What is a species • It used to be thought that anything that looked different were considered to be different species.
We now know that any given species has variation. • In the 1940’s scientists defined a species as a group of organisms that can interbreed and produce fertile offspring
Phylogenic Species Concept • Phylogeny- the evolutionary history of a species • The phylogenic species concept defines a species as a cluster of organisms that is distinct from other clusters and shows evidence of a pattern of ancestry and descent
But like all things they add to it • Phylogenetic species concept. This deals with species in terms of populations and ancestry. • It says two or more groups that evolve independently are classified as different species.
What's that funny P word mean? • Phylogeny- the evolutionary history of a species.
Remember all this classification starts with identifying characters • A Character is a inherited feature that can vary in a species.
There are 2 types of Characters you need to know. • Morphological Characters-The size, shape, and structure of an organism or one of its parts. Bone structure, coloration. • Biochemical Characters-molecular similarities and differences among organisms. Ex DNA, RNA
Quick Check! • What's a species? • We classify things based on their….? • What are the different types of characteristics? • Ok now I have all this classification stuff down what do I do with it??
Taxonomic Devices Phylogenetic Trees - a tree showing the evolutionary relationships among groups Cladograms - a diagram that represents the evolutionary tree of life - also includes characteristics Dichotomous Keys - a device used to identify organisms - uses couplets, which are pairs of highly organized statements
Cladistics • Cladistics is the method that classifies organisms according to the order that they diverged from a common ancestor.
CLADOGRAM “clade” a group of organisms that includes an ancestor and all descendants
Scientists use Cladistics to make a cladogram. • Cladistics-a method of classifying according to when they diverged from a ancestor. • A cladogram (aka phylogenetic tree)- is a branching diagram that shows a proposed evolutionary history.
What taxon is most closely related to birds? • Which taxon is least closely related to humans? • Which taxon has the least recent shared ancestors with humans?
Character types • Ancestral- a character found within the entire line of decedents • Derived-characters that are present in one group but not the ancestor
How to Build a cladogram. • http://ccl.northwestern.edu/simevolution/obonu/cladograms/Open-This-File.swf