Evolution and Microevolution Concepts

Evolution in Action

• Biston betularia (Peppered Moth)
  • Two main phenotypes: darkly colored and lightly colored moths.
  • Light-colored moths stand out in polluted environments, making them more susceptible to predation by birds.
  • During the Industrial Revolution, increased coal pollution led to a rise in dark-colored moths, as they survived better in darker environments due to natural selection.
  • In the mid-20th century, pollution control efforts led to cleaner air and lighter trees, resulting in a resurgence of the light-colored moths due to improved camouflage.

Antibiotic Resistance and Evolution

• Bacterial Evolution
  • Introduction of antibiotics since the late 1940s has led to increased resistance among bacteria.
  • Antibiotics initially kill susceptible bacteria, but some bacteria may have mutations that confer resistance, allowing them to survive and reproduce.
  • This phenomenon represents an arms race between humans and bacteria regarding antibiotic use.

Microevolution

• Microevolution Definition

  • Evolution occurs at the population level rather than the individual; populations evolve as mutations are passed down through generations.
  • Changes in allele frequencies equate to microevolution.
  • Mutation is the source of new alleles, affecting the gene pool—the total set of alleles in a population.

• Types of Mutations

  • Changes at the nucleotide level or in chromosomes can lead to different gene expressions (e.g., deletions, duplications, inversions).

Agents of Microevolution

1. Mutation

   • Introduces new alleles, can be neutral, harmful, or beneficial.

2. Gene Flow

   • Movement of alleles between populations via migration.
   • Example: Tar weeds and Hawaiian silver swords, where the seeds dispersed and their genetic relationship is analyzed despite physical differences.

3. Genetic Drift

   • Random changes in allele frequency; can result from events like disease or overhunting, leading to a genetic bottleneck.
   • Example: Feline immunodeficiency virus (FIV) and hunting pressures on elephant seals decreasing genetic diversity.

4. Non-Random Mating (Sexual Selection)

   • Certain traits are selected based on mate preference, affecting allele frequencies.
   • Example: Endler's guppies and peafowl mating decisions based on coloration or displays.

5. Natural Selection

   • Organisms with advantageous traits are favored, affecting reproductive success.
   • Types of natural selection:
     • Stabilizing Selection: Median traits favored; reduces extremes.
     • Directional Selection: One extreme trait favored, shifting populations.
     • Disruptive Selection: Both extremes favored, while median traits are selected against.

Real-World Examples of Selection

• Human Birth Weights

  • Median birth weights (around 6-7 lbs) are correlated with higher survival rates due to physical constraints of birth and early life viability.

• Cranial Capacity in Hominins

  • Increased cranial capacity from Australopithecus to Homo sapiens indicates evolutionary adaptation for cognitive abilities and problem-solving.

Conclusion

• Discussed evolution with examples including microevolutionary processes, natural selection dynamics, and impacts on populations over time.