Lecture 13: Homology, Characters and States

Anaplasy

*Independently* evolved functional similarity in different organisms - similarity may or may not be due to homoplasy of structures involved

Homoplasy

*Independently* evolved structure similarity in different organisms. - degree of similarity is due to environmental adaptations that have identical/similar selective forces - parallelism: come from relatively recent common ancestry - convergence: don't have lineages of recent common ancestry

Analogy

*Uniquely* evolved functional similarity in different organisms. - have corresponding homologues, but does not mean that homologous states have similar functions. - do not share a common ancestral origin

Homology

*Uniquely* evolved structural similarity in different organisms. - commonness of embryonic origin of 2 or more structures is used as evidence - degree of similarity is proportional to amount of evolutionary change that has occurred since they diverged from their common ancestral state.

What are the test of homology?

1. Similarity of special structure: similar in detail 2. Similarity of position: develop in same manner or occupy the same place in organisms relative to other character states 3. Conjunction: If homologous occur in the same organism, then specimen can ONLY HAVE 1 character state of that character.

Semaphorant

An individual specimen at a particular life history stage, which is needed for systematics = specimens must be in similar life stage.

Holomorphology

Total array of characters at ALL life stages.