Natural and Artificial Selection Notes

Core Principles of Evolution and Natural Selection

• Fundamental Theory of Evolution: Explains the process of biological change over time using the mechanism of natural selection. This theory describes how individual organisms adapt to their environment.
• Definition of a Population: A population is defined as a group of organisms belonging to the same species that live in the same geographic area at the same time.
• Natural Selection Definition: This is the process resulting in changes to the characteristics of a population of organisms over many generations. These changes occur because individuals possessing certain inherited traits survive specific local environmental conditions. Through the process of reproduction, these individuals pass on their alleles to their offspring.
• The Phrase "Survival of the Fittest": This phrase is used to explain natural selection, relating to how organisms that are the "fittest" leave behind the highest number of offspring, thereby winning the struggle for survival.
• Case Study: Life After Chernobyl: Observations of populations changing over time were evident to Darwin. A modern example includes the Grey Tit birds living near the site of the Chernobyl nuclear disaster. These birds have adapted to the high levels of radiation found in that specific area.
• Situational Nature of Natural Selection: Natural selection has no predetermined or set direction. A trait that is not beneficial in one environment or situation may become highly beneficial in another. Over generations, individuals inheriting beneficial alleles form a population better adapted to its environment.

Mechanisms and Requirements for Natural Selection

• Requirement of Variation: For natural selection to occur, there must be variation within a species. These variations manifest as structural, functional, or physiological differences between individual organisms.
• Survival and Reproduction: Individuals with helpful variations are more likely to survive and have a higher statistical chance of passing these variations to their offspring. Consequently, the variation becomes more common within the population.
• The V-I-D-A Model: Systematic biological change involves four key components:
  • Variation
  • Inheritance
  • Differential Survival and Reproduction
  • Adaptation

Types of Adaptations and Survival Strategies

• Adaptation: An adaptation is defined as a structure, behavior, or physiological process that assists an organism in surviving and reproducing within a particular environment.
• Camouflage: A structural adaptation used for avoiding predators by blending into the surroundings.
• Hibernation: A physiological adaptation allowing animals to survive harsh winters by conserving energy until food sources become available again.
• Mimicry: A strategy where a harmless species physically resembles a harmful or unpalatable species to deter predators.
  • Example: The Monarch butterfly is inedible to birds. The Viceroy butterfly is edible; however, predators avoid the Viceroy because its appearance is remarkably similar to the Monarch.

Genetic Origins of Variation and Mutation

• Sources of Variation: Variation results from an individual's genes and the genetic differences created through the processes of meiosis and sexual reproduction.
• Mutations: Mutations are changes in the DNA of an organism and are the only source of entirely new genetic information. They provide new alleles within a species.
• Occurrence of Mutations: Mutations occur randomly during DNA replication or through exposure to external factors such as UV radiation.
• Inheritance of Mutations: For a mutation to be passed on to future generations, it must occur within a gamete (reproductive cell).
• Beneficial vs. Harmful Mutations: While some mutations are harmful (such as those causing cancer), others are beneficial and provide a selective advantage.

Selective Pressure and Selective Advantage

• Selective Advantage: This is a genetic advantage that improves an organism's chances of survival, most often in a changing environment.
  • Example in Bacteria: Some bacteria can double their population in approximately $10\,min$. A new allele resulting from a random mutation might allow the entire population to survive if it provides a benefit against a threat.
• Selective Pressure: This is an environmental condition that selects for certain characteristics in individuals while selecting against others. These pressures can be:
  • Non-living factors: Abiotic environmental conditions.
  • Living factors: Predators, parasites, or competition for resources.
• Example of Antibiotic Resistance: An antibiotic is a chemical that kills bacteria and acts as a selective pressure. It selects for bacteria that possess the ability to resist the treatment. Surviving bacteria reproduce and pass the resistance gene to the next generation.

The Scientific Definition of Fitness

• Fitness: Refers to the relative contribution an individual makes to the next generation by producing offspring that survive long enough to reproduce themselves.
• High Fitness: An individual with greater fitness produces more offspring that survive to reproductive age, thereby continuing to pass on favorable alleles.

Artificial Selection

• Definition: Artificial selection occurs when selective pressure is exerted by humans on populations to improve or modify specific desirable characteristics.
• Human Intervention: Humans modify species over many generations by intentionally selecting and breeding individuals that possess traits they find desirable.
• Examples of Artificial Selection:
  • Crops: Selective breeding for yield and resilience.
  • Livestock: Breeding cows that produce higher volumes of milk.
  • Dogs: Breeding for specific aesthetic or functional traits.

Learning Resources and Review

• Video Resource: "Natural Selection in Action - Life After Chernobyl" (https://www.youtube.com/watch?v=YCd5XUeTglQ).
• Textbook Review Questions (Page 311): Questions # 1-7, 9, 13.
• Textbook Review Questions (Page 304): Questions # 1-3, 6-8, 10-13.