25.1: Tools for Studying Life's History: Phylogenic Trees
- Phylogeny: the branching evolutionary history of species or other groups of organisms
- Phylogenetic Tree: simplified diagram of this history
- Systematics: the discipline in biology that characterizes and classifies the relationships among all
organisms on earth, piecing together the tree of life
- Tree of life: the most universal of all phylogenetic trees
- Taxa: Higher level groups
- Relationships in phylogenetic trees must be estimated from the best available data
- Revised as new data becomes available
- Trait/Character: Any heritable genetic, morphological, physiological, developmental, or
behavioral characteristic that varies among the taxa to be studied
- Most phylogenetic analyses use molecular characters such as DNA nucleotide positions
- Morphological characters are typically the only characters available for phylogenetic
analyses of fossil taxa
- Data matrix: a table that allows you to score the character states of each taxon
- Outgroup: taxon that is not part of the taxonomic group being studied but is closely
related
- Help establish the direction of change of each character
- Ancestral trait: character that existed in an ancestor
- Derived trait: One that is a modified form of the ancestral trait, found in a descendant
- Originate via mutation, selection, and genetic drift
- Synapomorphy: a trait found in two or more taxa that is present in their most recent common
ancestor but is missing in more distant ancestors
- Allow biologists to recognize monophyletic groups (lineages)
- Monophyletic group: an evolutionary unit that includes an ancestral species and all of its
descendants but no others
- Complications with the model:
- This method assumes homology - that derived character states evolve only once and if
two organisms share this trait they must have inherited it from a common ancestor
- Homoplasy occurs when traits evolved independently in two or more different
lineages and are similar outside of ancestry
- Also assumes that reversals in character state do not occur
- Branches can gain traits and lose them - sometimes creating the appearance that
no change occurred
- People have developed methods to develop computer power to "filter" probable trees out of huge
pools of millions of possible trees
- Parsimony: filtering method that assumes that the most likely explanation or pattern is the
one that requires the fewest steps
- Biologists count the number of character changes required to produce each
pattern
- Evolutionary distance: acknowledges that more rapid evolutionary change may occur in
some branches than others
, - Maximum Likelihood and Bayesian Analysis: mathematical method - requires more
information then is provided in the data matrix - can produce relatively precise estimates
of evolutionary history
- Researches use a number of strategies to determine their confidence in their estimates tree results
- Convergent evolution: the independent evolution of similar traits in distantly related organisms
due to adaptation to similar environments and lifestyles
25.2: Tools for studying Life's History: The Fossil Record
- Fossil record provides direct evidence about what organisms that lived in the past looked liked,
lived, and when they existed
- Fossils can be used in phylogenetic analyses to study relationships
- Paleontologists: scientists who study fossils
- Fossils: pieces of physical evidence from an organism that lived in the past
- Fossil record: total collection of fossils that paleontologists have found throughout the world
- There are many processes in which things fossilize
- Fossils form only under particular conditions: organisms perish in an environment where they are
buried rapidly and the decompose slowly
- Therefore organisms that life above ground in dry forests, grasslands, and deserts are
much less likely to fossilize
- Slow decay is essential so things with bones are more likely to fossilize
- Recent fossils are much more recent than ancient fossils
- The older a fossil is the more likely it is exposed to destructive forces
- Organisms that are abundant and widespread leave much more evidence than do species that are
rare, local , or ephemeral
- Fossils are used to make a timeline of earth and life
- Earth was formed 4.6 billion years ago
- Life began 3.4 billion years ago
- Timeline:
- Precambrian: The time before life
- Oxygen was absent from the oceans and atmosphere for almost 2 billion years
after the origin of life
- Phanerozoic Eon: interval between 541 millions years ago and the present (divided into
three)
- Paleozoic era (ancient life): begins with the appearance of most major animal
lineages and ends with the obliteration of all life forms at the end of the Permian
period
- Mesozoic era (middle life): begins with the end-Permian extinction and ends with
the extinction of dinosaurs
- Cenozoic era (recent life): divided into the Paleogene, Neogene, and quaternary
periods - current life
- Anthropocene: a new epoch
- Reflects the dramatic physical, chemical, and biological changes that humans are causing
- Phylogeny: the branching evolutionary history of species or other groups of organisms
- Phylogenetic Tree: simplified diagram of this history
- Systematics: the discipline in biology that characterizes and classifies the relationships among all
organisms on earth, piecing together the tree of life
- Tree of life: the most universal of all phylogenetic trees
- Taxa: Higher level groups
- Relationships in phylogenetic trees must be estimated from the best available data
- Revised as new data becomes available
- Trait/Character: Any heritable genetic, morphological, physiological, developmental, or
behavioral characteristic that varies among the taxa to be studied
- Most phylogenetic analyses use molecular characters such as DNA nucleotide positions
- Morphological characters are typically the only characters available for phylogenetic
analyses of fossil taxa
- Data matrix: a table that allows you to score the character states of each taxon
- Outgroup: taxon that is not part of the taxonomic group being studied but is closely
related
- Help establish the direction of change of each character
- Ancestral trait: character that existed in an ancestor
- Derived trait: One that is a modified form of the ancestral trait, found in a descendant
- Originate via mutation, selection, and genetic drift
- Synapomorphy: a trait found in two or more taxa that is present in their most recent common
ancestor but is missing in more distant ancestors
- Allow biologists to recognize monophyletic groups (lineages)
- Monophyletic group: an evolutionary unit that includes an ancestral species and all of its
descendants but no others
- Complications with the model:
- This method assumes homology - that derived character states evolve only once and if
two organisms share this trait they must have inherited it from a common ancestor
- Homoplasy occurs when traits evolved independently in two or more different
lineages and are similar outside of ancestry
- Also assumes that reversals in character state do not occur
- Branches can gain traits and lose them - sometimes creating the appearance that
no change occurred
- People have developed methods to develop computer power to "filter" probable trees out of huge
pools of millions of possible trees
- Parsimony: filtering method that assumes that the most likely explanation or pattern is the
one that requires the fewest steps
- Biologists count the number of character changes required to produce each
pattern
- Evolutionary distance: acknowledges that more rapid evolutionary change may occur in
some branches than others
, - Maximum Likelihood and Bayesian Analysis: mathematical method - requires more
information then is provided in the data matrix - can produce relatively precise estimates
of evolutionary history
- Researches use a number of strategies to determine their confidence in their estimates tree results
- Convergent evolution: the independent evolution of similar traits in distantly related organisms
due to adaptation to similar environments and lifestyles
25.2: Tools for studying Life's History: The Fossil Record
- Fossil record provides direct evidence about what organisms that lived in the past looked liked,
lived, and when they existed
- Fossils can be used in phylogenetic analyses to study relationships
- Paleontologists: scientists who study fossils
- Fossils: pieces of physical evidence from an organism that lived in the past
- Fossil record: total collection of fossils that paleontologists have found throughout the world
- There are many processes in which things fossilize
- Fossils form only under particular conditions: organisms perish in an environment where they are
buried rapidly and the decompose slowly
- Therefore organisms that life above ground in dry forests, grasslands, and deserts are
much less likely to fossilize
- Slow decay is essential so things with bones are more likely to fossilize
- Recent fossils are much more recent than ancient fossils
- The older a fossil is the more likely it is exposed to destructive forces
- Organisms that are abundant and widespread leave much more evidence than do species that are
rare, local , or ephemeral
- Fossils are used to make a timeline of earth and life
- Earth was formed 4.6 billion years ago
- Life began 3.4 billion years ago
- Timeline:
- Precambrian: The time before life
- Oxygen was absent from the oceans and atmosphere for almost 2 billion years
after the origin of life
- Phanerozoic Eon: interval between 541 millions years ago and the present (divided into
three)
- Paleozoic era (ancient life): begins with the appearance of most major animal
lineages and ends with the obliteration of all life forms at the end of the Permian
period
- Mesozoic era (middle life): begins with the end-Permian extinction and ends with
the extinction of dinosaurs
- Cenozoic era (recent life): divided into the Paleogene, Neogene, and quaternary
periods - current life
- Anthropocene: a new epoch
- Reflects the dramatic physical, chemical, and biological changes that humans are causing
