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Honors Biology
Table of Contents
Unit 11 Overview: Evolution
11.1 Darwin's Theory and Natural Selection
11.2 Evidence for Evolution
11.3 Population Genetics and Hardy-Weinberg Equilibrium
11.4 Speciation and Macroevolution

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11.1 Darwin's Theory and Natural Selection

Citation:

Darwin's theory of natural selection revolutionized our understanding of life's diversity. It explains how organisms with advantageous traits survive and reproduce more, leading to population changes over time. This process drives evolution, shaping species to fit their environments.

Natural selection relies on variation within populations and the inheritance of traits. Competition for limited resources and overproduction of offspring intensify this process. Understanding these mechanisms is crucial for grasping how species evolve and adapt to their surroundings.

Natural Selection and Adaptation

Process of Natural Selection

  • Natural selection is the process by which organisms with favorable traits are more likely to survive and reproduce in a given environment
  • Occurs over many generations and results in changes in the characteristics of a population over time
  • Favorable traits that improve an organism's chances of survival and reproduction are called adaptations (camouflage, long necks in giraffes)
  • Fitness refers to an organism's ability to survive and reproduce in its environment, with higher fitness leading to a greater likelihood of passing on genes to future generations

Survival of the Fittest

  • "Survival of the fittest" is a phrase used to describe how natural selection favors organisms with traits that enhance their chances of survival and reproduction
  • Does not necessarily mean the strongest or most aggressive individuals survive; rather, it means those best adapted to their environment are more likely to survive and reproduce
  • Examples include birds with beaks adapted to specific food sources (finches in the Galapagos Islands) and insects with coloration that helps them blend into their surroundings (peppered moths)

Variation and Inheritance

Importance of Variation

  • Variation refers to the differences among individuals within a population, such as differences in size, color, or behavior
  • Variation is essential for natural selection to occur because it provides the raw material upon which selection can act
  • Sources of variation include mutations, genetic recombination during sexual reproduction, and environmental factors (nutrition, temperature)

Role of Inheritance and Competition

  • Inheritance is the passing of traits from parents to offspring through genes, which are segments of DNA that code for specific characteristics
  • Competition occurs when resources such as food, water, and space are limited, leading to a struggle for survival among individuals in a population
  • Overproduction refers to the tendency of organisms to produce more offspring than can survive, intensifying competition and driving natural selection (sea turtles laying hundreds of eggs)

Artificial Selection and Evolution

Artificial Selection and Selective Breeding

  • Artificial selection is the process by which humans select and breed organisms with desirable traits, leading to the development of new varieties or breeds over time
  • Selective breeding involves choosing individuals with specific characteristics to mate and produce offspring, with the goal of enhancing or combining desired traits in future generations
  • Examples of artificial selection include the development of different dog breeds (Chihuahuas, Great Danes) and the cultivation of crops with higher yields or resistance to pests (genetically modified corn)

Relationship between Artificial Selection and Evolution

  • Artificial selection demonstrates the power of selection to shape the characteristics of a population over time, providing a model for understanding how natural selection drives evolution
  • Domestication is the process by which humans have used artificial selection to modify wild species over many generations, resulting in organisms that are genetically distinct from their wild ancestors
  • Examples of domesticated species include dogs, cats, cattle, and various crop plants (wheat, rice, corn)

Key Terms to Review (18)

Phenotypic variation: Phenotypic variation refers to the observable differences in the physical traits, characteristics, and behaviors of individuals within a species. This variation can result from genetic differences, environmental influences, or interactions between the two, playing a crucial role in natural selection. Variations in traits like size, color, and shape can affect an organism's survival and reproduction, which are key components in the process of evolution.
Alfred Russel Wallace: Alfred Russel Wallace was a British naturalist and explorer who is best known for independently formulating the theory of evolution through natural selection, which he presented alongside Charles Darwin. His work provided critical evidence for the theory and highlighted the process of species adaptation to their environments, making significant contributions to the understanding of biodiversity and evolution.
Extinction: Extinction is the permanent loss of a species, meaning that there are no living individuals left to reproduce and maintain that species' population. This phenomenon can occur due to various factors, including environmental changes, habitat loss, overexploitation, and competition with other species. Extinction is a natural part of evolution but has been accelerated by human activities, leading to biodiversity loss and ecological imbalance.
Speciation: Speciation is the evolutionary process through which new biological species arise from existing species. This process often occurs when populations of the same species become isolated and undergo genetic changes over time, leading to the development of distinct characteristics that prevent interbreeding. The concept is closely linked to natural selection, as environmental pressures can drive the divergence of populations, and is further influenced by genetic variation within populations.
Genetic drift: Genetic drift is a mechanism of evolution that refers to random changes in allele frequencies within a population, particularly affecting small populations. This process can lead to significant evolutionary changes over time, especially when certain alleles become more or less common purely by chance, rather than through natural selection. It highlights how chance events can influence genetic variation and the evolutionary trajectory of a species.
Survival of the fittest: Survival of the fittest is a concept that refers to the idea that individuals or species best adapted to their environment are more likely to survive and reproduce. This phrase encapsulates the essence of natural selection, where advantageous traits enhance an organism's ability to thrive in its surroundings, thereby influencing the evolution of species over time.
Adaptive radiation: Adaptive radiation is an evolutionary process in which organisms rapidly diversify and adapt to a variety of ecological niches. This phenomenon often occurs when a single ancestral species spreads into different environments, leading to the emergence of new species that are uniquely adapted to their specific habitats and lifestyles. This process highlights the relationship between environmental factors, natural selection, and the diversification of life forms.
Charles Darwin: Charles Darwin was an English naturalist and biologist best known for his theory of evolution through natural selection. His ideas laid the foundation for understanding how species adapt and evolve over time, influencing various scientific fields including ecology, genetics, and behavior.
Descent with modification: Descent with modification is the process by which species evolve over time, passing traits from parent to offspring while undergoing changes in their characteristics. This concept is fundamental to understanding evolution, as it emphasizes that all living organisms share a common ancestry and that adaptations occur through natural selection. Essentially, it explains how species can diverge from their ancestors, leading to the diversity of life we see today.
Gene flow: Gene flow is the transfer of genetic material between populations through processes like migration and interbreeding. This movement of alleles can significantly affect the genetic diversity of populations, introducing new genetic variations and influencing evolutionary changes over time.
Stabilizing selection: Stabilizing selection is a type of natural selection that favors intermediate phenotypes over extreme variations, promoting the stability of a population by reducing variation. This process helps maintain the status quo in traits that are advantageous for survival and reproduction, leading to a decrease in the extremes of a trait spectrum. In this way, stabilizing selection can enhance the overall fitness of a population, ensuring that successful traits are preserved through generations.
Directional Selection: Directional selection is a type of natural selection that favors one extreme phenotype over other phenotypes in a population, leading to a shift in the population's traits in a specific direction. This process can result from environmental changes or shifts in resource availability, causing a selective pressure that enhances the reproductive success of individuals with advantageous traits. As a result, these traits become more common in the population over time, illustrating the dynamic nature of evolution.
Natural selection: Natural selection is the process by which organisms that are better adapted to their environment tend to survive and produce more offspring. This mechanism drives evolution by favoring traits that enhance survival and reproduction, leading to gradual changes in species over generations. It connects to understanding variations in populations, the evidence supporting evolutionary theory, genetic principles, and the emergence of new species.
Biogeography: Biogeography is the study of the distribution of species and ecosystems across geographic space and through geological time. It explores how environmental factors and historical events shape the patterns of biodiversity we see today. This field helps us understand how species adapt to their environments and how isolation or connectivity between regions can influence evolutionary processes.
Fossil record: The fossil record is the collection of all known fossils and their placement in the geological time scale, which provides evidence for the history of life on Earth. It serves as a crucial tool in understanding how species have changed over time and how they relate to one another, contributing to the framework of evolutionary biology and the mechanisms of natural selection.
Mutation: A mutation is a permanent change in the nucleotide sequence of an organism's DNA, which can result in alterations to genes and the proteins they encode. These changes can arise from various factors such as errors during DNA replication, exposure to radiation, or chemical mutagens. Mutations play a crucial role in evolution and genetic diversity, impacting everything from individual traits to population dynamics.
Experiment: An experiment is a structured procedure conducted to test a hypothesis, gather data, and analyze outcomes in order to draw conclusions about a particular phenomenon. Experiments are fundamental in scientific research as they allow for the systematic manipulation of variables to determine cause-and-effect relationships. This structured approach is crucial for validating or refuting scientific theories and advancing knowledge across various fields.
Hypothesis: A hypothesis is a proposed explanation for a phenomenon, serving as a foundation for experimentation and testing within scientific inquiry. It is often formulated based on prior knowledge and observations, allowing researchers to predict the outcome of an experiment. A well-constructed hypothesis helps guide the research process by providing a clear focus and direction for data collection and analysis.