M16L2 Modern Classification Systems

This typological species concept is based on the idea that species are unchanging, distinct, and natural types.

Biological species concept

•It does not account for extinct species or species that reproduce asexually. Also, some species, such as wolves and dogs, are known to interbred.

•This is the species concept used throughout this unit.

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​•Phylogeny is the evolutionary history of a species.

•This definition solves some of the problems of earlier concepts because it applies to extinct species and species that reproduce asexually.

•It also incorporates molecular data.

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​Phylogenetic Species Concept

Anatomical (Structural) Similarities
Size, shape, color

​​Morphological Characters

​​Biochemical Characters

Similarities in DNA= shared ancestry

Molecular clocks are used to compare DNA sequences between species. The more mutations present, the more time has passed.

•Mutation rates are affected by many factors, making molecular clocks difficult to read.​

•A cladogram is a branching diagram that represents a proposed phylogeny of a species or group.
One branch of a cladogram is called a clade.

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The more derived characteristics two groups share, the more recently the groups shared a common ancestor.

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​Cladograms/Phylogenetic Trees

•Darwin used an analogy of a tree to suggest that all species developed from one or a few species.

•The term tree of life was coined in the nineteenth century to describe a diagram showing all living organisms.