Notes

• Defining Evolution


  Evolution is defined as the change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes that are passed on from parent to offspring during reproduction. Different characteristics tend to exist within any given population as a result of mutation, genetic recombination and other sources of genetic variation.
• Who proposed the theory of Darwinian evolution?

  Charles Darwin and Alfred Russel Wallace
• What is the primary mechanism driving evolution according to Darwinian evolution?

  Natural selection
• How do organisms with advantageous traits affect future generations?

  They are more likely to survive and reproduce
• What happens to a population's characteristics over time due to natural selection?

  They gradually change
• How does natural selection work in a population of beetles?

  • Some beetles are green, others brown
  • Birds eat more visible green beetles
  • Brown beetles survive and reproduce more
  • Population shifts towards more brown beetles over time
• Lamarckism: 


  This earlier theory, proposed by Jean-Baptiste Lamarck, suggested that acquired characteristics during an organism's lifetime could be inherited by its offspring. For example, Lamarck believed that giraffes developed long necks by stretching to reach high branches, and this trait was then passed to their offspring. This is incorrect; acquired traits are not heritable in the way Lamarck proposed. Changes to an organism's DNA are required for evolution to occur.
• Acquired Non-genetic Changes: 


  It's crucial to understand that changes acquired during an organism's lifetime, such as increased muscle mass from exercise or calluses on hands, are not considered evolution. These changes are not encoded in the organism's DNA and therefore cannot be passed on to the next generation.
• Molecular Evidence: 


  The analysis of DNA and protein sequences provides compelling evidence for common ancestry. Closely related species will have more similar DNA and protein sequences than distantly related species.
• DNA/RNA Base Sequences: 


  By comparing the order of nucleotide bases (A, T, C, G) in DNA or RNA molecules from different species, scientists can quantify the degree of similarity. Higher similarity suggests a more recent common ancestor. The more differences there are, the more distant the common ancestor.
• Phylogenetic Trees: 


  Sequence data (DNA, RNA, or amino acid) is used to construct phylogenetic trees, which are branching diagrams that illustrate the evolutionary relationships between different species. These trees are based on the principle that species with more similar sequences are more closely related. The branching points on the tree represent common ancestors.
• Selective Breeding as Evidence for Evolution


  Selective breeding, also known as artificial selection, provides strong evidence for evolution. It demonstrates how rapid evolutionary changes can occur in a relatively short time. Humans have been selectively breeding plants and animals for thousands of years, choosing individuals with desirable traits and breeding them together. This process leads to the accumulation of these traits in subsequent generations, resulting in significant changes from the original wild species.
• Variations in Domesticated Species: 


  Compare the diversity of dog breeds (from tiny Chihuahuas to giant Great Danes) or the variety of cultivated crops (e.g., different types of apples, corn, or wheat). These variations arose through selective breeding, highlighting the potential for rapid evolutionary change.
• Rapid Evolutionary Changes: 


  The speed at which new breeds and varieties are developed through selective breeding is much faster than the timescale of natural selection in the wild. This is because humans actively choose which individuals reproduce, accelerating the process of evolutionary change.
• Comparison with Wild Species: 

  By comparing domesticated breeds with their wild ancestors, we can observe the extent of the changes that have occurred through selective breeding. For example, compare the size, coat color, and behavior of domesticated dogs to wolves, their wild ancestors. The differences are striking and demonstrate the power of selective breeding to alter characteristics.
• Morphological Evidence:


  Morphological evidence, based on the study of the form and structure of organisms, also supports evolution. Two key concepts are homologous and analogous structures.
• Homologous Structures: 

  These are structures that share a common evolutionary origin, even if they have different functions in different species. They provide evidence of divergent evolution, where a common ancestor gives rise to species with different adaptations.
• Pentadactyl Limb: 


  The pentadactyl limb (five-fingered or five-toed limb) is a classic example of a homologous structure. It is found in a wide range of vertebrates, including humans, bats, whales, and cats. Although the limb's function varies greatly (e.g., grasping, flying, swimming, walking), the underlying bone structure is remarkably similar, suggesting a common ancestor.
• Analogous Structures: 


  These are structures that have similar functions but different evolutionary origins. They provide evidence of convergent evolution, where unrelated species develop similar adaptations in response to similar environmental pressures. For example, the wings of birds and bats are analogous structures; both are used for flight, but they have different evolutionary origins (bird wings are modified forelimbs, while bat wings are modified hands). The similarity in function is due to similar selective pressures, not common ancestry.
• Speciation Mechanisms


  Speciation is the only mechanism by which new species arise. It's important to distinguish speciation from gradual changes within a single species.
• An Example of Convergent Evolution: 


  analogous structures are a good example of convergent evolution, where similar environmental pressures lead to the development of similar traits in unrelated species. The wings of insects and birds are a classic example; both are used for flight, but their evolutionary origins are completely different. The similarity in function is due to convergent evolution, not shared ancestry. Other examples include the streamlined bodies of sharks (fish) and dolphins (mammals), or the similar cactus-like forms found in unrelated desert plants.
• • Speciation Increases Species Count: 


  Each successful speciation event increases the total number of species on Earth. This process is a fundamental driver of biodiversity.
• Speciation


  Speciation is the evolutionary process by which populations evolve to become distinct species. It's the splitting of a pre-existing species into two or more distinct species. This process results in an increase in the total number of species.
• What is differential selection in speciation?

  Different traits are favored in different environments
• How do differential selection pressures lead to speciation?

  They cause reproductive isolation and new species formation
• What is an example of differential selection leading to speciation?

  • Birds split into two groups
  • One group inhabits forests
  • The other group inhabits grasslands
  • Different beak shapes evolve
  • Resulting in two distinct species
• What could happen to a population of birds in different habitats over time?

  They may evolve different traits and become distinct species
• What is the result of different selection pressures in habitats?

  Evolution of different beak shapes and sizes
• What is a consequence of reproductive isolation?

  Formation of new species
• How does the environment influence trait selection in populations?

  Different environments favor different traits
• Gradual Change vs. Speciation: 


  It's crucial to understand that gradual changes in the characteristics of a single population, without the formation of new, reproductively isolated species, is not speciation. For example, the gradual increase in the average size of a bird species over many generations is not speciation; it's simply evolutionary change within a single species. Speciation requires the formation of new, distinct species that are reproductively isolated from each other.