Chapter 25 – History of Life on EarthChapter 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 26.3 HierarchicalHierarchicalclassificationclassification

Carolus LinnaeusBinomial nomenclature

• TaxonomyTaxonomy: The theory and : The theory and practice of classifying organismspractice of classifying organisms

• SystematicsSystematics: The scientific study : The scientific study of the diversity of organismsof the diversity of organisms

• PhylogenyPhylogeny: Evolutionary history : Evolutionary history of a group of organismsof a group of organisms

PhylogenyPhylogeny

• A branching diagram that depicts a A branching diagram that depicts a hypothesishypothesis about the evolutionary history of a species or about the evolutionary history of a species or a group of species over geologic timea group of species over geologic time

Descent with modification:Evolutionary tree of elephant family, based on fossil evidence)

Phylogeny of finches on the Galápagos Islands

26.5 How to read a phylogenetic tree

26.4The connection between classification and phylogeny.

Hierarchical classification is reflected in progressively finer branching of the phylogenetic treeMost 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 26.10 Monophyletic versus paraphyletic and polyphyletic groupsMonophyletic 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 Modern systematics is shaking some phylogenetic treesphylogenetic trees

Thus the class Reptilia, in its traditional form, is paraphyleticThus the class Reptilia, in its traditional form, is paraphyletic

26.11 Constructing a phylogenetic tree26.11 Constructing a phylogenetic tree

Ancestral (=homologous) trait: A trait shared due to common ancestryAncestral (=homologous) trait: A trait shared due to common ancestry

Derived trait: A trait that differs from a common ancestorDerived 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 taxonomyCladistics 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 Convergent evolution and analogous (=homoplastic) structuresanalogous (=homoplastic) structures: : Homoplasy - Not all similarity represents common ancestry!Homoplasy - Not all similarity represents common ancestry!

The Ocotillo (SW U.S.A) and Allauidia (Madagascar) are not closely related. The Ocotillo (SW U.S.A) and Allauidia (Madagascar) are not closely related. Resemblance due to independent adaptations to similar environmental Resemblance due to independent adaptations to similar environmental pressures.pressures.

See also 26.7

Chapter 25 – History of Life on EarthChapter 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. 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 In this phylogenetic tree, C and D are closest related because D are closest related because

theytheyA. do not share a common

ancestor with O, A, or B.

B. occupy different islands

C. evolved from a common ancestor a long time ago.

D.have the greatest number of anatomical similarities as shown by statistical analysis

E. share the most derived traits

DCBA

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