Unit 7.1-7.3

Key Concepts of Natural Selection

  • Definition: Natural selection is a process where organisms with favorable traits are more likely to survive and reproduce compared to others, influencing the evolution of species over time.

  • Charles Darwin: An English naturalist known for his research in the Galapagos Islands that contributed significantly to the theory of evolution through natural selection.

    • Research Focus: Biogeography and the diversification of species, particularly finches introduced from South America to the Galapagos.

  • Darwin's Quote: Highlights the ongoing nature of natural selection as it assesses variations in organisms continuously, shaping species over long periods.

Myths About Natural Selection

  1. Natural Selection Provides What Organisms Need:

    • FALSE: It does not provide needs; it acts on existing genetic variations that result in survival and reproduction.

  2. Natural Selection Acts for the Good of a Species:

    • FALSE: It has no intentionality; traits that enhance survival may not be beneficial for the species' long-term health. E.g., predators could overuse resources leading to starvation.

  3. Organisms Actively Adapt to Their Environment:

    • FALSE: Adaptation occurs through random mutations in genetic variations, not conscious effort by the organism.

  4. “Survival of the Fittest” Refers to the Strongest Creatures:

    • FALSE: "Fittest" refers to the organisms that survive and reproduce, not just those that are physically strong or healthy. E.g., individuals with sickle cell anemia may survive malaria but are not considered healthy.

The Process of Evolution

  • Descent with Modification: A modern definition of evolution describing how heritable traits change over generations.

    • Evolution: A change in the genetic makeup of a population over time.

Key Observations in Natural Selection

  1. Heritable Traits:

    • Traits can be passed from parents to their offspring, influencing evolutionary change.

    • Adaptations: Features that enhance survival and reproduction.

  2. More Offspring Than Can Survive:

    • Leads to competition for resources and results in differential survival, where favorable traits are selected for in the population.

    • Evolution Occurs in Populations, Not Individuals: Changes accumulate at the population level over generations.

Artificial Selection vs. Natural Selection

  • Natural Selection: Influences traits through natural processes in the environment.

  • Artificial Selection: Involves human intervention to breed organisms for desired traits, seen in domesticated plants and animals.

Application of Concepts

  • Example Scenario:

    • A population of pacas losing body mass due to environmental changes illustrates descent with modification as the population adapts in response to limited food resources.

Convergent Evolution: instances where unrelated species develop similar adaptations to environmental challenges, such as the wings of bats and birds evolving independently to facilitate flight.

Examples of organisms with convergent evolution -

  • Dolphins, sharks, and Catfish : Both sharks and dolphins, as well as catfish, have evolved streamlined bodies and fin structures adapted for aquatic life.

  • Cacti and Euphorbias: Both have adapted to arid environments with thick, fleshy stems to store water and spines for protection against herbivores.

  • Antifreeze proteins in Arctic fish and some insects: These adaptations allow them to survive in freezing temperatures, showcasing a similar evolutionary response to cold environments.

Practice Questions:

Plant species A is stimulated to produce flowers in response to warming weather in the Spring. Plant species B is
stimulated to produce flowers when hours of daylight become longer in the Spring. Which species would be most
affected by the selective mechanism of Climate Change? Explain your reasoning.

  • Plant species A would likely be more affected by the selective mechanism of Climate Change, as its flowering is directly tied to temperature increases, which could be more variable than day length. This variability can create mismatches with pollinator activity and seasonal life cycles.

A farmer uses DDT to kill insects in his field. The first year nearly all of the insects were killed. By the fourth year,
however, nearly all of the insects survived the DDT treatment.
Explain the process of natural selection in this population of insects. Include these words - mutation, phenotype,
variation, resistance, adaptation, and differential survival.

The farmer's use of DDT (dichlorodiphenyltrichloroethane) in his fields illustrates the process of natural selection among the insect population over several years.

Initially, when DDT was introduced, it effectively killed nearly all of the insect population. This significant decrease in numbers resulted in a selective pressure on the remaining population. In the following years, a few insects likely survived the DDT treatment due to natural variation in their phenotypes, which resulted from random mutations.

  1. Mutation: Some insects in the population may have had genetic mutations that conferred resistance to the effects of DDT.

  2. Variation: These mutations created variation within the population, leading to different phenotypes where certain individuals could withstand the toxic effects of DDT while others could not.

  3. Resistance and Adaptation: Over time, the insects that survived were those with resistant phenotypes. This resistance allowed these individuals to reproduce and pass on their advantageous traits to their offspring, leading to an adaptation in the population where more insects developed this resistance to DDT.

  4. Differential Survival: As a result of differential survival, the frequency of resistant insects increased in the population over the years. By the fourth year, nearly all of the insects were those that had the mutation for DDT resistance, showcasing a complete shift in the population's genetic makeup in response to the selection pressure imposed by the pesticide.

In conclusion, the process of natural selection in this insect population demonstrates how mutation, variation, and differential survival can lead to rapid adaptation in response to environmental changes, such as pesticide application.