Unit 20: Evolution & Classification
The diversity of life has evolved and continues to evolve by natural selection.
There is overwhelming evidence for the evolution of life on Earth.
Gene pools change over time.
Species are named and classified using an internationally agreed system.
The identification of organisms can be aided with the use of a dichotomous key.
Evolution occurs when heritable characteristics of species change.
Natural selection can only occur if there is variation among members of the same species
Species tend to produce more offspring than the environment can support.
Variations can be discrete or continuous
Mutation, meiosis and sexual reproduction cause variation between individuals in a species
Individuals that reproduce pass on characteristics to their offspring
Individuals that are better adapted tend to survive and produce more offspring while the less well adapted tend to die or produce fewer offspring
Adaptations are characteristics that make an individual suited to its environment and way of life
Natural selection increases the frequency of characteristics that make individuals better adapted and decreases the frequency of other characteristics leading to changes within the species
Changes in beaks of finches on Daphne Major
Development of melanistic insects in polluted areas
Evolution of antibiotic resistance in bacteria
Use theories to explain natural phenomena- the theory of evolution by natural selection can explain the development of antibiotic resistance in bacteria
Some strains of bacteria have evolved with genes that confer resistance to antibiotics and some strains of bacteria have multiple resistance
Identifying examples of directional, stabilizing and disruptive selection
Evidence for Evolution
The fossil record provides evidence for evolution
Selective breeding of domesticated animals shows that artificial selection can cause evolution
Evolution of homologous structures by adaptive radiation explains similarities in structure when there are differences in function
Comparison of the pentadactyl limb of mammals, birds, amphibians, and reptiles with different methods of locomotion
Looking for patterns, trends and discrepancies- there are common features in the bone structure of vertebrate limbs despite their varied use
Continuous variations across the geographical range of related populations matches the concept of gradual divergence
Species are groups of organisms that can potentially interbreed to produce fertile offspring
A gene pool consists of all the genes, and their different alleles, present in an interbreeding popul.
Members of a species may be reproductively isolated in separate populations
Reproductive isolation of populations can be temporal, behavioral or geographic
Comparison of allele frequencies of geographically isolated populations
Speciation in the genus Allium by polyploidy
Looking for patterns, trends and discrepancies- patterns of chromosomes number in some genera can be explained by speciation due to polyploidy
Populations of a species can gradually diverge into separate species by evolution
Evolution required that allele frequencies change with time in populations
Speciation due to divergence of isolated populations can be gradual.
Speciation can occur abruptly
In a natural classification, the genus and accompanying higher taxa consist of all the species that have evolved from one common ancestral species.
Natural classification helps in identification of species and allow the prediction of characteristics shared by species within a group.
A clade is a group of organisms that have evolved from a common ancestor.
Cladograms are tree diagrams that show the most probable sequence of divergence in clade.
Cladograms including human and other primates.
Analysis of cladograms to deduce evolutionary relationships.
Evidence for which species are part of a clade can be obtained from the base sequences of a gene or the corresponding amino acid sequence of a protein.
Taxonomists sometimes reclassify groups of species when new evidence shows that a previous taxon contains species that have evolved from different ancestral species.
Evidence from cladistics has shown that classifications of some groups based on structure did not correspond with the evolutionary origins of a group or species.
Reclassification of the figwort family using evidence from cladistics.
Falsification of theories with one theory being superseded by another- plant families have been reclassified as a result of evidence from cladistics.
Sequence differences accumulate gradually so there is a positive correlation between the number of differences between two species and the time since they diverged from a common ancestor.
Traits can be analogous or homologous.
Production of ascorbic acid by some mammals, but not others that need a dietary supply.
Falsification of theories with one theory being superseded by another—scurvy was thought to be specific to humans, because attempts to induce the symptoms in laboratory rats and mice were entirely unsuccessful.