Chapter 25 – History of Life on Earth Chapter 26 – Phylogeny and the Tree of Life Early Earth (a brief history of time & the Big Bang) Introduction to prokaryotes Geologic time scale, important events in the history of life Fossil record – dating Impact of geology on biology of today Volcanoes, meteors, continental drift Prehistoric/historic extinctions Systematics/Phylogeny (Ch. 26) Cladogram, derived/ancestral traits, outgroups Major lineages of life

26.3 Hierarchical classification Carolus Linnaeus Binomial nomenclature

Taxonomy: The theory and practice of classifying organisms Systematics: The scientific study of the diversity of organisms Phylogeny: Evolutionary history of a group of organisms

Phylogeny A branching diagram that depicts a hypothesis about the evolutionary history of a species or a group of species over geologic time

Phylogeny of finches on the Galápagos Islands

26.5 How to read a phylogenetic tree

26. 4 The connection between classification and phylogeny 26.4 The connection between classification and phylogeny. Hierarchical classification is reflected in progressively finer branching of the phylogenetic tree Most recent common ancestor of all members of the weasel (Mustelidae) and dog (Canidae) families Most recent common ancestor of coyotes and gray wolves

Cladogram: A phylogenetic diagram that classifies organisms according to shared characteristics (common descent). [it uses two-way branch points connected by a common ancestor] Clade: that portion of the evolutionary tree that is decended from a common ancestor (the ancestor plus all its descendants)

26.10 Monophyletic versus paraphyletic and polyphyletic groups Monophyletic group (or clade): Ancestral species plus all of its descendant species Paraphyletic group: Ancestral species but not all of its descendant species Polyphyletic group: Lacks the common ancestor (doesn’t include all descendants)

Modern systematics is shaking some phylogenetic trees Thus the class Reptilia, in its traditional form, is paraphyletic

26.11 Constructing a phylogenetic tree Ancestral (=homologous) trait: A trait shared due to common ancestry Derived trait: A trait that differs from a common ancestor Outgroup: A species (or a group of species) from an evolutionary lineage that diverged before the lineage of the species we are studying

Cladistics and taxonomy The finer the branching, the smaller the taxonomic unit.

26.12. Branch lengths can indicate relative amounts of genetic change. 26.13. Branch lengths can indicate time (based on the fossil record).

26.14. The principle of maximum likelihood. The phylogenetic tree that represents the most likely sequence of evolutionary events is the one that should be used. The principle of parsimony. The phylogenetic tree that presents fewer changes in the same trait is more likely to be accurate.

Convergent evolution and analogous (=homoplastic) structures: Homoplasy - Not all similarity represents common ancestry! See also 26.7 The Ocotillo (SW U.S.A) and Allauidia (Madagascar) are not closely related. Resemblance due to independent adaptations to similar environmental pressures.

Chapter 25 – History of Life on Earth Chapter 26 – Phylogeny and the Tree of Life Early Earth (a brief history of time & the Big Bang) Introduction to prokaryotes Geologic time scale, important events in the history of life Fossil record – dating Impact of geology on biology of today Volcanoes, meteors, continental drift Prehistoric/historic extinctions Systematics/Phylogeny Cladogram, derived/ancestral traits, outgroups Major lineages of life

Concept 26.6. Continuous revisions of our understanding of the tree of life. See also Whittaker, Science (1969)

26. 21. The three domains of life 26.21. The three domains of life. Branch lengths are proportional to the amount of genetic change in each lineage. Lineages with multi-cellular organisms shown in red

Chapter 26 - Review 26.1. Phylogenies show evolutionary relationships 26.2. Phylogenies are inferred from morphological and molecular data 26.3. Shared characters are used to construct phylogenetic trees 26.4 and 26.5 – skip 26.6. Continuous revisions of the tree of life

In this phylogenetic tree, C and D are closest related because they do not share a common ancestor with O, A, or B. occupy different islands evolved from a common ancestor a long time ago. have the greatest number of anatomical similarities as shown by statistical analysis share the most derived traits A B C D O

Time magazine cover story “Scientists figured out decades ago that chimps are our nearest evolutionary cousins, roughly 98% to 99% identical to humans at the genetic level. When it comes to DNA, a human is closer to a chimp than a mouse is to a rat.” http://www.time.com/time/magazine/article/0,9171,1541283,00.html