Evolution: Natural Selection and Key Concepts

Evolution: Key Concepts

• Evolution refers to the gradual change in organisms' inherited traits across generations.
• Biological evolution involves changes in the frequency of heritable characteristics within populations through time.
• The theory posits that all organisms are related through a common ancestor.
• Speciation describes the process by which new species arise from existing ones.

Darwin’s Theory of Evolution by Natural Selection

• Charles Darwin, considered the "Father of Evolution," proposed the theory of natural selection.
• Species display variation globally, locally, and over time, with examples being rheas, Galapagos finches, and fossils.
• Natural selection favors organisms whose traits allow them to survive and reproduce.
• The struggle for existence results from overproduction of offspring, leading to a fight for resources.
• Survival of the fittest means individuals with advantageous traits are more likely to reproduce.
• Advantageous traits are heritable, increasing fitness and are passed to offspring.
• Artificial selection, where humans select desired traits, informed Darwin’s understanding of natural selection.

Evidence for Evolution

• The fossil record demonstrates changes in life over time, showing resemblances to living species and extinct species.
• Similar species in different geographical locations suggest common ancestry, such as finches on the Galápagos Islands.
• Homologous structures, like mammalian forelimbs, indicate divergent evolution from a common origin.
• Analogous structures, such as bird and insect wings, exemplify convergent evolution with similar functions but different origins.
• Vestigial structures, like the human appendix, are functionless remnants of evolutionary past.
• Embryological similarities in early development implies shared ancestry among different species.
• The universal use of DNA and ATP among organisms supports the theory of a common ancestor.

Mechanisms of Evolution

• Mutations in DNA can introduce new traits and can be neutral, harmful, or beneficial.
• Genetic drift causes random changes in allele frequencies, particularly in small populations, through the bottleneck and founder effects.
• Gene flow involves the movement of genes between populations via migration.
• Non-random mating, or sexual selection, occurs when mating preferences are based on specific traits.
• Natural selection increases the prevalence of traits that enhance fitness within a population.

Types of Natural Selection

• Directional selection favors one extreme phenotype, such as larger beaks during drought.
• Stabilizing selection favors the average phenotype, exemplified by human birth weight.
• Disruptive selection favors both extreme phenotypes over the average, like black and white rabbits.

Speciation

• Speciation is the process of forming new species, requiring reproductive isolation.
• Behavioral isolation occurs when differing courtship rituals prevent mating.
• Geographic isolation happens when physical barriers separate populations.
• Temporal isolation arises when species reproduce at different times.
• Darwin’s finches demonstrate how geographic isolation and adaptation can lead to new species.

Population Genetics

• A gene pool is comprised of all the alleles in a population.
• The Hardy-Weinberg principle describes a non-evolving population under five conditions: large population size, no migration, no mutations, random mating, and no natural selection.
• Genetic equilibrium means allele frequencies remain stable over time.

Influential Scientists in Evolutionary Theory

• James Hutton proposed gradualism, suggesting Earth's changes occur slowly.
• Charles Lyell expanded on Hutton's work with uniformitarianism, stating that the same geological processes that shape Earth today also shaped it in the past.
• Thomas Malthus observed that populations grow faster than the resources, leading to competition.
• Jean-Baptiste Lamarck believed traits acquired during life could be inherited (incorrect).
• Charles Darwin introduced the theory of evolution by natural selection.

Examples of Evolution

• During the Industrial Revolution, dark-colored peppered moths became more common due to pollution.
• Insects exhibit pesticide resistance due to natural selection.
• Darwin’s finches evolved different beak shapes to adapt to varied food sources on the Galápagos Islands.

Key Terms

• Adaptation is a heritable trait which improves an organism's fitness.
• Fitness is an organism's overall ability to survive and reproduce.
• Alleles are the variant forms of a gene.
• Gene flow signifies the movement of genes between populations.
• Genetic drift refers to random changes in allele frequencies within small populations.
• Mutation defines a change in the DNA sequence.
• Vestigial structures are those that have lost their original function, such as the appendix.