Evolution: Definition, Forces, Misconceptions

Definition & Forces of Evolution

• Evolution involves a shift in allele frequencies within a population over successive generations
• The four primary drivers of evolution are natural selection, genetic drift, gene flow, and mutation

Common Misconceptions

• Evolution lacks a pre-set objective
• Evolution acts at the population level, not on individual organisms
• Evolution does not inherently imply advancement or progress
• Natural selection is one of several mechanisms of evolution

Philosophical & Historical Foundations

• Asimov's "The Relativity of Wrong" states that scientific understanding evolves and becomes more refined, much like evolutionary theory
• Confirmation bias is the tendency to favor information that supports existing beliefs
• Evolution serves as an explanatory science by providing insights into historical patterns, although its predictions are probabilistic rather than definitive

Historical Figures & Theories

• Scala Naturae is a hierarchical view of life that classified all things, has been supplanted by evolutionary relationships
• Lamarck’s theory is flawed because it did not account for traits being inherited nor evidence of an inherent drive to complexity
• Malthus noted that population growth is limited by finite resources, influencing natural selection
• Darwin's Galapagos finches and observed species diversity supported natural selection
• Both Darwin and Wallace discovered natural selection independently, with Wallace emphasizing biogeography
• Natural selection’s logic relies on variation, inheritance, differential survival, and adaptation
• Fitness is defined as an organism's reproductive success
• Darwin's theory lacked knowledge of genetic inheritance until Mendelian genetics was introduced

Genetics & Variation

• Genotypic and phenotypic variation provide the necessary raw material for evolution
• Mutation is the origin of genetic variation

Types of Mutations

• Neutral mutations have no effect

• Deleterious mutations are harmful, such as frameshift mutations

• Beneficial mutations are advantageous, such as antibiotic resistance

• Point mutations involve a single base change that can be silent, missense, or cause nonsense

• Frameshift mutations involve insertions or deletions that alter the reading frame

Mechanisms of Evolution

• Genetic drift is the random fluctuation of allele frequencies, mainly impacting small populations
• The founder effect results in a loss of genetic diversity when a new population is established
• A bottleneck event is a sharp reduction in population size that reduces genetic variation
• Natural selection facilitates adaptation through differential survival
• Neutral Theory (Kimura) posits that many mutations are neutral and spread via genetic drift
• A cline is a gradient of genetic variation across a geographic range
• Effective population size (Ne) versus total population size (N) is affected by factors like sex ratio and genetic diversity
• FST and FIS statistics quantify population differentiation and inbreeding
• Gene flow involves the movement of alleles between populations, which counteracts drift and increases variation

Dispersal Mechanisms

• Passive dispersal involves mechanisms like wind and water
• Active dispersal involves movement by the organism itself
• Genetic drift reduces variation whereas gene flow increases it
• Climate change alters selective pressures and population connectivity

Adaptive vs. Vulnerable Traits

• Adaptive traits include high genetic diversity and phenotypic plasticity
• Vulnerable traits include low genetic diversity and specialized habitat needs

Key Thinkers & Contributions

• Aristotle contributed early life classification systems
• Charles Darwin discovered natural selection as the mechanism of evolution
• Alfred Russel Wallace discovered biogeography and natural selection
• Carl Linnaeus developed binomial nomenclature and classification
• Thomas Malthus discussed population limits and resource competition
• Jean-Baptiste Lamarck had early ideas of evolution via acquired traits
• Charles Lyell established uniformitarianism
• Louis Pasteur disproved spontaneous generation
• Gregor Mendel discovered the laws of inheritance

Genetics Fundamentals

• Haploid cells have one set of chromosomes, while diploid cells have two sets
• Mitosis is for growth/repair, whereas meiosis is for gamete formation
• Central dogma explains DNA converting into RNA which converts into protein
• The Hardy-Weinberg equilibrium predicts allele frequencies in non-evolving populations
• Genes located closely together on the same chromosome are inherited together
• Pleiotropy occurs when one gene influences multiple traits

Essential Terms & Concepts

• Fact is observation, theory is well-substantiated explanation, and hypothesis is testable prediction
• Falsification is a key principle in science
• Empirical evidence comes from observation/experimentation
• Natural theology is the pre-evolutionary idea of species' fixed nature
• Uniformitarianism is the idea that past geological processes operate today
• Variation and fitness are crucial for natural selection
• Genetic drift and the founder effect cause random changes in allele frequency
• A bottleneck effect results in reduced genetic diversity
• Gene flow and migration introduce new genetic material into populations
• Hardy-Weinberg equilibrium means no evolution occurs if conditions are met
• FST and FIS measure population differentiation and inbreeding