Lecture 2: Tree of Life

evolution describes _____

change over time

gradualism

gradual change leads to large differences over time

evolution occurs at the ____ level

population

natural selection

changes are caused by heritable differences affecting an organism’s ability to survive and reproduce

Darwin’s hypothesis of common descent

states that all life, living or extinct, has descended without interruption from one or a few original forms

goal of evolutionary biology

reconstruct or assemble the “tree of life”

all life shares a single-celled ancestor that lived ____ years ago

3-4 billion

2 sources of data to construct the evolutionary tree

1. fossils

2. living organisms

ancestors and ancestral traits are ____ to phylogenies

implicit

what are phylogenies useful for

• infer evolutionary relationships among species, strains, individuals

• reconstruct the evolutionary origins and divergence of key traits

• trace human origins and migrations

• forensics and criminology

• deduce the sources and carriers of diseases

phylogenetic tree

branching diagram that represents a hypothesis about the evolutionary history of a group of organisms

root of phylogenetic tree

represents the ancestral lineage

branch tips of phylogenetic tree

represent the most recent descendants of that ancestor

evolutionary lineage

sequence of ancestral organisms leading to a particular descendant taxon

branch point (node)

represents a common ancestor and the divergence of two evolutionary lineages from that common ancestor (speciation)

common ancestor

ancestral organism that gave rise to two or more descendant lineages

most recent common ancestor (MRCA)

youngest relative from which all lineages in the group are directly descended

two species are more related if they have a _____ common ancestor

more recent

clade (monophyletic groups)

grouping that includes a common ancestor and all the descendants of that ancestor

paraphyletic group

consists of an ancestral species and some but not all of its descendants

polyphyletic group

includes distantly related species but does not include their most recent common ancestor

sister taxa

• groups that share a common ancestor that is not shared by any other group

• more closely related to each other than any other taxon

phylogenies group organisms into taxa by ____

specific characters

taxon

systemic unit or group to which organisms are assigned

characters

• variable features of an organism: multiple character states are used to infer phylogenies

• can be phenotypes/traits or genotypes

phenotype

morphological, physiological, biochemical, behavioral features or properties of an organism (aka. traits)

genotype

specific set of genes/DNA sequences (alleles) possessed by an individual

genotype and environment determine the ____ of individuals

phenotype

the best phylogenetic tree is …

the one that postulates the fewest evolutionary change

5 general patterns of morphological evolution based on decades of data from phylogenetics

1. most features of organisms have been modified from preexisting features

2. different traits/characters evolve at different rates

3. evolution is often gradual

4. homoplasy is common

5. many lineages contain adaptive radiations

1. most features of organisms have been modified from preexisting features

• related organisms have homologous characters that have been inherited from an equivalent structure in a common ancestor

• most complex structures and traits do NOT evolve de novo, but are modified from ancestral traits

2. different traits/characters evolve at different rates

• mosaic evolution: species dont evolve as a whole; individual traits can evolve in a piecemeal fashion and at different rates

• conserved characters: traits or structures that change little over evolutionary time

3. evolution is often gradual

• evolutionary gradations in form are often observed

4. homoplasy is common

• homoplasy: similarity in a specific trait/character without shared ancestry

• opposite of homology

• exists because of convergent evolution

convergence

superficially similar features that have independently evolved in separate lineages

5. many lineages contain adaptive radiations

• adaptive radiations: periods of rapid formation of a new species whose adaptation allow them to fill different ecological roles

• often occur when a species invades open and diverse habitats