Natural Selection and Speciation

Natural Selection

• Natural selection is the process where organisms better adapted to their environment tend to survive and produce more offspring.
• This leads to changes in the genetic makeup of a population over time.
• Key factors driving natural selection include:
  • Variation in traits within a population.
  • Inheritance of these traits.
  • Differential survival and reproduction based on these traits.
• Natural selection acts on existing variations within a population; it does not create new traits.
• Selective pressures can be environmental factors like:
  • Predation
  • Competition for resources
  • Climate change
• Examples of adaptations due to natural selection:
  • Camouflage in animals
  • Antibiotic resistance in bacteria
  • Beak shape variations in finches

Speciation

• Speciation is the evolutionary process by which new biological species arise.
• There are several mechanisms of speciation:
  • Allopatric speciation: occurs when a population is geographically isolated, leading to genetic divergence due to different selective pressures.
  • Sympatric speciation: occurs when a new species arises within the same geographic area, often due to factors such as:
    • Polyploidy (extra sets of chromosomes)
    • Sexual selection
    • Habitat differentiation
• Key factors in speciation:
  • Reproductive isolation: the inability of different species to interbreed and produce fertile offspring.
  • Genetic divergence: differences in gene pools between populations.
  • Geographic isolation or ecological factors
• Speciation is a gradual process, taking millions of years.

Mutation and Genetic Drift

• Mutations are random changes in the DNA sequence.
• Mutations can be beneficial, neutral, or harmful, affecting traits.
• Mutations are a source of new genetic variations in a population.
• Genetic drift is a random change in allele frequencies within a population, particularly evident in small populations.
• Genetic drift can lead to the loss or fixation of alleles, regardless of their adaptive value.
• Two key types of genetic drift are:
  • Bottleneck effect: drastic reduction in population size due to events like natural disasters. This results in a loss of genetic diversity.
  • Founder effect: when a small group of individuals establishes a new population in a new area, potentially carrying alleles that are different from the original population.

Evidence of Evolution

• Fossil records provide evidence of past life forms and show the evolutionary history of organisms.
• Fossil succession: fossils appear in a specific order in the rock layers.
• Comparative anatomy: the study of similarities and differences in the anatomy of different species shows common ancestry.
  • Homologous structures: similar structures derived from a common ancestor, even if their function differs. (e.g., human arm, bat wing).
  • Analogous structures: structures that have similar functions but are not derived from a common ancestor. (e.g., wing of a bird and wing of a butterfly).
• Comparative embryology: comparison of the embryonic development of different species can reveal similarities and evolutionary relationships.
• Molecular biology: comparisons of DNA and protein sequences provide powerful evidence of evolutionary relationships between species.
• Biogeography: patterns of distribution of species across the globe reflect their evolutionary history.
• The theory of evolution explains patterns of biodiversity, adaptations, and the unity of life.
• Transitional fossils are a key component of supporting evolution.
• Vestigial structures are structures in organisms that have lost most of their original function through evolution.