BIO 205: Phylogenetics

Monophyletic

Includes an ancestor and all descendants. This is the gold standard for classification.

Polyphyletic

Includes an ancestor and some, but not all, descendants (e.g., traditional "Reptiles," which left out birds).

Paraphyletic

A group composed of organisms from distinct lineages that do not share a immediate common ancestor (often grouped mistakenly due to convergent traits).

Features of a Phylogenetic Tree

Tips/Taxa, Branches, Nodes

Tips/Taxa

The operational taxonomic units (modern species or fossils being studied).

Branches

The lines representing evolutionary lineages passing through time.

Nodes

The branching points representing the most recent common ancestor of the descendants.

Clades

A common ancestor and all of its descendants. - Monophyletic Group

Groups on Trees: Monophyletic

Complete Family

Groups on Trees: Paraphyletic

Missing descendent - is left out when grouping

Groups on Trees: Polyphyletic

Unrelated groups

Homology

A trait shared by species because it was inherited from a common ancestor (e.g., the limb bones of humans, bats, and whales).

Homoplasy

A shared trait that evolved independently via convergent evolution, not from a shared ancestor (e.g., the wings of birds and insects).

The Red Queen Hypothesis

That species must constantly adapt, evolve, and proliferate in order to survive while pitted against ever-evolving opposing species