A4.1:  Evolution and Speciation

Theme:  Unity and Diversity

The tools and methods used to study evolution and speciation demonstrate how scientific investigation uncovers both themes:

• Comparing DNA and protein sequences reveals both the shared evolutionary history that connects all life and the specific branching patterns that created current biodiversity
• Studying homologous structures shows both the common ancestry that unites related organisms and the diverse adaptations that have evolved for different functions and environments
• Selective breeding programs demonstrate both the universal principles of evolutionary change and the specific outcomes that result from different selection pressures and genetic starting points
• Biogeographic evidence, like the separation of bonobos and chimpanzees by the Congo River, show both the universal process of geographic speciation and the specific environmental factors that drive evolutionary divergence
• Investigating barriers to hybridization and hybrid sterility reveals both the common mechanisms that maintain species boundaries and the diverse ways different groups have evolved reproductive isolation
• Studies of plant speciation through polyploidy demonstrate both the shared genetic mechanisms that can create new species and the specific pathways that have generated plant diversity

Unity:

• Evolution as change in heritable characteristics of populations applies to all life form
• DNA, RNA, and protein sequences provide powerful evidence that all organisms descended from common ancestors with the same genetic code 
  
• Natural selection operates through the same basic principles across all species
• Homologous structures demonstrate that diverse organisms share common structural blueprints inherited from shared ancestors
• All new species arise through the splitting of pre-existing species, with reproductive isolation and differential selection operating as universal mechanisms
• All evolutionary change depends on heritable genetic variation
  

Diversity:

• Species can form through various processes including allopatric speciation with geographic isolation, sympatric speciation without geographic barriers, and abrupt speciation through hybridization and polyploidy, showing the diverse ways new species can arise
• Single ancestral species can rapidly diversify into multiple species adapted to different ecological niches
• There are multiple ways to prevents gene flow between diverging populations
• Domesticated animals and crop plants show how quickly populations can change when subjected to strong selection pressures, creating dramatic diversity within species in relatively short time periods
• Some groups undergo rapid adaptive radiation while others remain relatively unchanged for millions of years, and some species form gradually while others arise abruptly, showing the diverse tempo of evolution

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.

• What is the evidence for evolution?
• How do analogous and homologous structures exemplify commonality and diversity? 

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​Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• How does the theory of evolution by natural selection predict and explain the unity and diversity of life on Earth?
• What counts as strong evidence in biology? 

Key Terms to Know: * higher level only

Adaptive Radiation*
Alleles*
Allopatric Speciation*
Amino Acid Sequence
Analogous Structure
Acquired Characteristics
Base Sequence
Behavioral Isolation*
Biodiversity*
Bonobo
Chimpanzee
Common Ancestry
Congo River
Convergent Evolution
Crop Plant
Darwin

Differential Selection
Divergent Evolution
Deoxyribonucleic Acid (DNA)
Domesticated Animal
Evolution
Extinction
Falsify
Geographical Isolation
Gradual Evolutionary Change
Heritable
Homologous Structure
Hybridization*
Interspecific Hybrids*
Knotweed*
Lamarck
Niche

Pentadactyl Limb
Polyploidy*
Population
Pragmatic Truth
Protein
Reproductive Isolation
Rna
Selective Breeding
Speciation
Species
Sterility*
Sympatric Speciation*
Temporal Isolation*
Theory
Variation

A4.1.1— Evolution as change in the heritable characteristics of a population.  

• Define evolution.
• Distinguish between Lamarckism and Darwinian evolution. 
• Outline evolution via natural selection as a paradigm shift in biology.​

A4.1.2— Evidence for evolution from base sequences in DNA or RNA and amino acid sequences in proteins.

• State that similarities and differences between DNA, RNA and amino acids sequences can be evidence for evolution. 
• Discuss sequence data showing evidence for evolution within a species.
• Outline the relationship between time, evolutionary relationships and biological sequence (nitrogenous base or amino acid) similarities between species.

A4.1.3— Evidence for evolution from selective breeding of domesticated animals and crop plants.

• Define artificial selection. 
• List reasons why humans have selectively bred domesticated animals and crop plants. 
• Outline how selective breeding can lead to rapid evolutionary change..
• Explain an example of artificial selection in a crop plant. 
• Explain an example of artificial selection in a domestic animal.

A4.1.4—  Evidence for evolution from homologous structures.

• Define homologous structure.
• List examples of different types of homologous structures at different levels of biological organization.
• Define pentadactyl limb.
• List the bone structures present in the pentadactyl limb (specific names of bones are not required).
• Identify pentadactyl limb structures in diagrams of amphibians, reptiles, birds and mammals. 
• Relate differences in pentadactyl limb structures to differences in limb function. 
• Define divergent evolution. 
• Describe how divergent evolution explains the pattern found in pentadactyl  limb structure yet allows for the specialization of different limb functions.​

A4.1.5— Convergent evolution as the origin of analogous structures. 

• Define analogous structure.
• State an example of an analogous structure found in two species.
• Outline how convergent evolution results in analogous structures.​
• Interpret cladograms to determine if traits are homologous or analogous.
  

A4.1.6-- Speciation by splitting of pre-existing species.

• Define speciation.
• Compare the process of speciation with that of gradual evolutionary change in an existing species.
• State the impact of speciation and extinction on the total number of species on Earth. 

A4.1.7— Roles of reproductive isolation and differential selection in speciation.

• List two processes required for speciation to occur.
• Define reproductive isolation. 
• Outline how reproductive isolation and differential survival lead to speciation.
• Outline the speciation between chimpanzees and bonobos.

AHL A4.1.8— Differences and similarities between sympatric and allopatric speciation.

• Compare allopatric and sympatric speciation.
• Explain temporal, behavioral and geographic isolation as mechanisms of reproductive isolation.
• Describe an example of temporal, behavioral and geographic reproductive isolation.

AHL A4.1.9— Adaptive radiation as a source of biodiversity.  

• Outline the cause and consequence of adaptive radiation.
• Outline an example of adaptive radiation as a source of biodiversity.

AHL A4.1.10— Barriers to hybridization and sterility of interspecific hybrids as mechanisms for preventing the mixing of alleles between species.

• Define interspecies hybrid.
• Describe the example of a mule as an infertile interspecies hybrid.
• State why organisms have evolved barriers to prevent interspecies hybridization. 
• Outline pre- and post-zygotic mechanisms to prevent interspecies hybridization.

AHL A4.1.11—  Abrupt speciation in plants by hybridization and polyploidy.   

• ​​Define polyploidy.
• Outline the cause of polyploidy.
• Compare autopolyploidy to allopolyploidy.
• Explain how polyploidy can lead to abrupt speciation.
• Outline an example of speciation due to polyploidy.