Evolution Flashcards

11.1 Discovering How Populations Change

• Evolution is the process through which allele and genotype frequencies change over time in a population, leading to changes in phenotype frequencies.

Early Ideas

• Early scientists and philosophers generally did not believe that species changed over time.
• Jean-Baptiste Lamarck proposed that individuals could change based on their environment, and these acquired characteristics could be inherited by offspring.

Evolution is Proposed

• Charles Darwin and Alfred Wallace presented papers on evolution by natural selection in 1858.

Charles Darwin

• Darwin traveled the world on the H.M.S. Beagle from 1831 to 1836.
• Observed ground finches in the Galápagos Islands with variations in beak size and shape adapted to different food sources.

Alfred Russell Wallace

• Wallace traveled to Brazil (1848-1852) and the Malay Archipelago (1854-1862).
• Identified the Wallace Line, a biogeographic boundary in Indonesia with distinct species on either side.

Wallace's Line

• A biogeographic boundary separating Asian and Australian fauna.
• Located between Bali and Lombok in Indonesia, where a sudden change in species occurs.
• Reflects historical landmass connections and rising sea levels after the last Ice Age.
• Islands west of the line have species of Asian origin, while those east have species of Australian origin.

Natural Selection

• Darwin and Wallace independently proposed that species change over time.
• Natural selection is the mechanism explaining how and why these changes occur.
• Based on three principles:
  • Inheritance: Characteristics are passed from parent to offspring.
  • Limited Resources: More offspring are produced than can survive, leading to competition.
  • Variation: Offspring vary in their characteristics, and these variations are inherited.
• Outcome:
  • Offspring with beneficial inherited traits are more likely to survive and reproduce.
  • The traits of successful individuals become more prevalent in the next generation.

Darwin’s Finches

• Observed natural selection in finches on the Galápagos Islands.
• Medium ground finches have inherited variation in bill shape; some have wide, deep bills, and others have thinner bills.
• Large-billed birds are more efficient at eating large, hard seeds, while smaller-billed birds are more efficient at eating small, soft seeds.
• During a 1977 drought, vegetation changed, and mostly large, hard seeds were available.
• Large-billed birds survived better, and the average bill size in the population increased the following year.

Variation

• Natural selection requires variation among individuals in a population.
• These differences must have a genetic basis to be heritable.
• Mutation is the ultimate source of new genetic variation.
  • Mutations can be beneficial, harmful, or neutral.
• An adaptation is a heritable trait that aids survival and reproduction in an organism's environment.

Patterns of Evolution

• Divergent evolution occurs when two species evolve in different directions from a common point.
  • Homologous structures are similar structures inherited from a common ancestor but may have different functions.
• Convergent evolution occurs when similar structures arise independently in different species.
  • Analogous structures are similar in function and appearance but not inherited from a recent common ancestor.

The Modern Synthesis

• Integrates the theory of evolution with genetics.
• Allows for microevolution, which includes small-scale genetic changes in a population over time.

Macroevolution

• Involves major evolutionary events that cause significant changes in a population over time.
• Can lead to speciation, the formation of two species from one original species which requires the new species to be unable to interbreed.
  • Allopatric speciation occurs when geographically separated populations evolve independently until they can no longer interbreed.
  • Sympatric speciation involves speciation occurring within a single population of a parent species, in one location.

Population Genetics

• Population genetics studies what happens to the alleles in a population over time.
• The gene pool is all of the alleles in a population.
• The Hardy-Weinberg equilibrium states that a population’s allele and genotype frequencies will remain the same unless some evolutionary force acts upon the population.

11.2 Mechanisms of Evolution

• Mechanisms of evolution include mutation, gene flow, genetic drift, and natural selection.

Selection

• Natural selection selects for beneficial alleles that allow for environmental adaptation.
  • Adaptive traits increase fitness, allowing individuals to survive and reproduce more.
• Artificial selection occurs when humans determine the fitness of individuals in a population based on their traits.
  • Selective breeding of crops, livestock, and pets.
• Sexual selection occurs when fitness of certain traits is determined by different levels of reproductive success due to mate choice.
  • Leads to the evolution of dramatic traits that often appear maladaptive in terms of survival but persist because they allow greater reproductive success.

Mutation

• Mutation is the ultimate source of new genetic variation, although the mutation rate is quite low.
• Beneficial mutations become more common over time due to selection.
• Harmful mutations may be removed or remain at very low frequencies.
• Neutral mutations are not affected by selection but can be affected by gene flow and genetic drift.

Genetic Drift

• Genetic drift changes in a population’s allele or genotype frequencies due to random chance.
• Most significant in small populations.

Genetic Drift: Bottleneck Effect

• The bottleneck effect occurs when a disaster randomly kills a large portion of a population.
• The genetic makeup of the survivors determines the gene pool, which may differ significantly from the original population.
• Rare alleles are likely to be lost during bottleneck events.

Genetic Drift: Founder Effect

• A founder effect occurs when a portion of a population leaves to start a new population in a new location, or if a population gets divided by a physical barrier.
• The new population contains only a subset of the genetic variation found in the parent population.

Gene Flow

• Gene flow is the movement of alleles into and/or out of a population.
• Due to the movement of individual organisms or gametes.
• When individuals move between populations it is referred to as migration.

11.3. Evidence of Evolution

• Scientists have collected extensive evidence supporting the theory of evolution for over 150 years.

Evidence

• Fossil evidence
• Anatomical
• Embryological
• Biogeographical
• Molecular

Fossils

• Fossils are mineralized, or preserved, remains of organisms from the past.
• The fossil record shows the evolution of form over millions of years.
• Transitional fossils show intermediate forms between earlier and later species.

Comparative Anatomy

• Comparing the anatomy of species provides evidence of their evolutionary relationships.
• Homologous structures have a similar pattern or layout due to being inherited from a common ancestor.
• Vestigial structures have no apparent function in current species but are evidence of descent from an ancestor species with that structure.

Comparative Embryology

• Embryology studies an organism’s development from a zygote to its adult form.
• Ancestral traits are often retained in embryonic stages and are shared among species with a common ancestor.

Biogeography

• The geographic distribution of organisms follows patterns that are best explained by examining evolution as it relates to the movement of tectonic plates over geological time.
• Isolated islands tend to have high numbers of endemic species due to their evolution in isolation from other species.

Molecular Biology

• Evidence of a common ancestor for all of life is reflected in the universality of DNA as the genetic material, the near universal genetic code, similar enzymes used in all DNA replication, and the expression of genes.
• The evolutionary relatedness of organisms is reflected in the similarity of their DNA sequences.

11.4 Common Misconceptions about Evolution

Misconception 1 - Evolution Is Just a Theory

• Critics imply that there is little evidence supporting it and that it is still in the process of being rigorously tested.
• A scientific theory is a concept that has been extensively tested and supported with a lot of data over time.
• Evolution is a scientific theory with extensive evidence supporting it.

Misconception 2 - Individuals Evolve

• An individual is born with a specific set of genes that do not change as the individual ages.
• Evolution is the change in genetic makeup of a population over time, so populations evolve.

Misconception 3 - Evolution Explains the Origin of Life

• The theory of evolution explains how populations change over time and how life diversifies, not how life came to exist.
• It does not explain how life began or how the first cells originated.

Misconception 4 - Organisms Evolve on Purpose

• The mechanisms of evolution act on variation that already exists in a population.
• Variation does not arise in response to organism’s needs or wants.
• Populations are not evolving towards a goal. The fossil record shows that populations evolve in response to environmental conditions and random events.

Misconception 5 - Evolution Is Thought to Be Controversial Among Scientists

• Evolution is nearly universally accepted among biologists today due to the overwhelming body of evidence supporting it.

Keywords

• adaptation
• allopatric speciation
• analogous structure
• bottleneck effect
• convergent evolution
• divergent evolution
• embryology
• fossils
• founder effect
• gene flow
• gene pool
• genetic drift
• Hardy-Weinberg equilibrium
• homologous structure
• inheritance of acquired characteristics
• macroevolution
• microevolution
• migration
• modern synthesis
• mutation
• natural selection
• population genetics
• speciation
• sympatric speciation
• variation
• vestigial structure