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3: Evolutionary Mechanisms and the Diversity of Life

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    3883

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    • 3.0: Introduction
      This page examines the diversity of organisms and the evolutionary mechanisms behind it, contrasting historical views with a modern scientific understanding of species. It highlights the observation of cruel behaviors and anatomical similarities among species, raising questions about common ancestry versus independent creation. Darwin's naturalistic perspective on biological phenomena is emphasized.
    • 3.1: Organizing organisms (hierarchically)
      This page discusses Carl Linnaeus's hierarchical classification system for organisms, which is based on observed traits and reproductive compatibility. Despite its lack of theoretical underpinning, it sparked debates on classification criteria. Linnaeus's work culminates in a phylogenetic "tree," highlighting life's interconnectedness. The page also emphasizes the difference between laws and theories in biology, underscoring the evolving nature of scientific models.
    • 3.2: Natural and un-natural groups
      This page explores biological classification, noting that while species are naturally defined, higher categories like genera and families may lack biological relevance. It highlights the often arbitrary criteria used for classification, relying on traits such as size and cranial features. The role of evolution and synapomorphies in defining groups is emphasized, along with the complexities of determining ancestry.
    • 3.3: Fossils and family relationships: introducing cladistics
      This page discusses the fossil record, noting that only a small percentage of organisms, primarily those with skeletons, are preserved. It highlights exceptions in classification, such as Ediacarian organisms, and mentions research on Neanderthal and Denisovan DNA to explore their relationship with modern humans. The summary underscores the importance of Darwin's theory of evolution through natural selection in understanding biological history.
    • 3.4: Evolution theory’s core concepts
      This page outlines the fundamental aspects of the Theory of Evolution, emphasizing the importance of observed variations in traits and their inheritance. It discusses how controlled breeding demonstrates the resemblance between offspring and parents, which supports the concept of heritable traits. The text highlights artificial selection through examples like domestication of corn and dog breeds.
    • 3.5: So what do we mean by genetic factors?
      This page discusses hereditary factors in offspring, exemplified by the Hapsburg lip in inbred royal families, which resulted in disabilities. It also explains artificial selection in domesticated animals, leading to exaggerated traits and increased vulnerability in the wild, with examples such as chickens, turkeys, corn, and chihuahuas, highlighting human influence on survival traits.
    • 3.6: Limits on populations
      This page explores superfecundity in organisms, explaining that species can reproduce excessively, exceeding sustainable population levels. It references Thomas Malthus on resource limitations and behaviors that reduce competition. Environmental factors significantly impact population dynamics and stability.
    • 3.7: The conceptual leap made by Darwin and Wallace
      This page discusses how Darwin and Wallace formulated the concept of natural selection by studying heredity, reproduction, and environmental constraints. They emphasized that reproductive success, influenced by factors like mate accessibility and survival against threats, drives the frequency of phenotypic traits. The complexity of evolutionary processes is further underscored by the intricate relationships between traits and environmental factors, complicating the genotype-phenotype interaction.
    • 3.8: Mutations and the origins of genotype-based variation
      This page examines the origin and variation of genetic material, likening the genome to a book of 3.2 billion characters. It underscores the role of genes and the impact of intragenic regions on genetic function. The content discusses human genetic variation, polymorphisms, and the contribution of meiosis to unique genetic combinations during reproduction. Overall, it highlights the complexity and importance of genotypic differences in heredity.
    • 3.9: The origins of polymorphisms
      This page explains that genomic variations among individuals result from DNA replication errors and environmental factors, leading to approximately 100-200 new mutations each generation. While most errors are corrected, these mutations contribute to genetic diversity, creating new alleles and polymorphisms that can influence phenotypes. Recognizing these processes is essential for understanding genetic inheritance and variation in populations.
    • 3.10: A short aside on the genotype-phenotype relationship
      This page explores the complexities of genetic traits, distinguishing between discrete traits (e.g., blood type) and continuous traits (e.g., height, weight). It explains that discrete traits have clear distinctions, whereas continuous traits vary within populations, using statistical measures for analysis.
    • 3.11: Variation, selection, and speciation
      This page discusses how genetic variation within a population influences reproductive success and allele frequency changes over generations. It highlights that advantageous genotypes increase in prevalence, while disadvantageous ones may decline. The effects of alleles on reproduction are shaped by genotype interactions, traits, and environmental factors. Strongly beneficial alleles are favored, while harmful ones face selection against, particularly affecting survival before reproduction.
    • 3.12: Types of simple selection
      This page outlines three types of selection: stabilizing, directed, and disruptive. It explains how genetic variation and environmental changes affect trait distribution in populations. Stabilizing selection favors average traits, directed selection shifts trait means towards advantageous values, and disruptive selection favors extreme traits, which can lead to subpopulation formation and speciation.
    • 3.13: A short note on pedagogical weirdness
      This page discusses the Hardy-Weinberg equilibrium, a key principle in population genetics that explains the stability of allele frequencies in non-evolving populations based on five unrealistic assumptions. It cites the contributions of G.H. Hardy and Wilhelm Weinberg, challenging prior beliefs about allele dominance. Additionally, it emphasizes the complexity of allele-trait relationships and invites readers to reflect on the limitations of these theories in real-world populations.
    • 3.14: Population size, founder effects and population bottlenecks
      This page explores evolutionary processes, focusing on the Hardy-Weinberg equilibrium, founder effect, and population bottlenecks. It highlights how small, isolated populations experience genetic drift, leading to distinct traits unaffected by natural selection. The text also discusses the implications of allele distribution on future evolution and examines human migration and genetic diversity, particularly the complexity of African populations versus derived groups.
    • 3.15: Population bottlenecks
      This page covers population bottlenecks, significant reductions in population size due to environmental changes like asteroid impacts or pathogens, which can lead to mass extinctions. It explains that survivors may be selected randomly or for advantageous traits, causing non-random genetic changes and increased genetic drift. Additionally, it discusses the importance of neutral genetic polymorphisms in tracing human population history and migrations, highlighting early population bottlenecks.
    • 3.16: Genetic drift
      This page explains genetic drift as a significant evolutionary force that results in the fixation of alleles, including non-functional ones like the gulo1 gene, affecting primates' vitamin C dependency. It highlights the impact of random processes in small populations and how genetic drift, alongside founder and bottleneck effects, can alter evolutionary trajectories and future adaptations, stressing the role of existing genetic variation in these processes.
    • 3.17: Gene linkage: one more complication
      This page discusses how the organization and linkage of genes impact evolution, affecting allele selection and reproductive success. While Mendel's research emphasized independent genes, the reality shows that genetic loci influence phenotypes and that gene linkage can also lead to harmful alleles becoming fixed. Evolution tends to favor gene combinations that enhance reproductive success, which may result in traits that seem maladaptive from a human viewpoint.
    • 3.18: A brief reflection on the complexity of phenotypic traits
      This page discusses the classification of traits as adaptive, non-adaptive, or maladaptive, explaining that adaptive traits improve reproductive success. It also addresses how some deleterious alleles may persist due to pleiotropy, where a gene impacts multiple traits, and emphasizes that the effects of traits can vary in different environments, indicating that traits should be assessed contextually rather than as strictly beneficial or harmful.
    • 3.19: Speciation and extinction
      This page explores the Theory of Evolution, detailing how speciation and ecological niches contribute to the diversity of life. It emphasizes the process by which populations evolve into distinct species influenced by reproductive success and environmental pressures, including competition. The competitive exclusion principle is introduced, indicating that two species cannot coexist in the same niche.
    • 3.20: Mechanisms of speciation
      This page explores the processes of speciation, emphasizing allopatric speciation through population isolation and adaptation to distinct niches. It addresses how evolution is a perpetual process shaped by environmental changes that can cause extinctions and alter ecological niches. The Red Queen hypothesis is introduced, highlighting the interconnectedness of species, particularly in predator-prey dynamics, which drive evolutionary adaptations.
    • 3.21: Isolating mechanisms
      This page examines the effects of cross-breeding between populations adapted to different ecological niches, highlighting disadvantages for offspring and heightened selective pressure against hybrids. It uses examples like Darwin’s finches and Hawaiian honeycreepers to illustrate the connection between behavioral and physical traits, such as feeding preferences and beak shape.
    • 3.22: Sympatric speciation
      This page discusses sympatric speciation, where a single population evolves into two distinct, reproductively isolated groups in the same area. Initially debated, it can occur through mechanisms like host selection, leading to varied mating behaviors and reproductive isolation. These conditions create different selective pressures, promoting adaptability and the emergence of separate species through disruptive and sexual selection processes.
    • 3.23: Signs of evolution: homology and convergence
      This page explains the difference between homologous and analogous traits in evolutionary biology, noting that homologous traits stem from a common ancestor, while analogous traits develop independently due to evolutionary convergence.
    • 3.24: The loss of traits
      This page discusses the complexities of determining evolutionary relationships, emphasizing the distinction between homologous (shared ancestry) and convergent (independent origin) traits. It highlights how evolution can lead to the loss of traits that no longer aid reproductive success, particularly in parasitic organisms.
    • 3.25: Signs of evolutionary history
      This page discusses evolution as a continuous experiment shaped by random mutations and selective pressures on reproductive success. It emphasizes that traits are products of past adaptations, not ideal designs, often reflecting compromises made over time. Factors influencing evolution are both selective and non-selective, constrained by costs and benefits.
    • 3.26: Homologies provide evidence for a common ancestor
      This page discusses the concept of homologous structures as evidence for evolutionary relationships and highlights advancements in molecular methods, such as genome sequencing, that allow for the comparison of gene sequences.
    • 3.27: Anti-evolution arguments
      This page discusses the theory of evolution, highlighting its contentious nature regarding human origins and life's essence. It emphasizes that despite controversies, there is extensive evidence supporting the idea that all organisms evolved from common ancestors through established evolutionary processes.

    Contributors and Attributions

    • Michael W. Klymkowsky (University of Colorado Boulder) and Melanie M. Cooper (Michigan State University) with significant contributions by Emina Begovic & some editorial assistance of Rebecca Klymkowsky.

    This page titled 3: Evolutionary Mechanisms and the Diversity of Life is shared under a not declared license and was authored, remixed, and/or curated by Michael W. Klymkowsky and Melanie M. Cooper.