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Questions and Answers
What describes the combination of alleles present in an organism?
Which of the following statements is a consequence of natural selection?
What was a significant observation made by the Grants regarding the Galápagos finches?
What term is used to describe the enhanced likelihood of an organism surviving and reproducing due to favorable traits?
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Which concept explains the struggle for survival among members of a population?
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What is the phenomenon where a significant portion of a population is randomly killed, leading to a drastic change in genetic structure?
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Which term describes the introduction of new alleles into a population due to migration?
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What can enhance the effect of genetic drift, particularly in small populations?
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What is defined as the evolution of similar structures independently in different species?
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According to the biological definition of species, what primarily distinguishes one species from another?
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What is an adaptation in the context of evolution?
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How does natural selection affect beak sizes in finches during environmental changes?
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Which statement best describes genetic drift?
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What role do mutations play in evolution?
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What is the primary difference between an adaptation and acclimation?
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Study Notes
Evolution by Natural Selection
- Natural Selection: the mechanism by which populations evolve.
- Limited Resources: Struggle for survival due to limited resources leads to differential survival and reproduction.
- Favorable Traits: Individuals with traits better suited to the environment are more likely to survive and reproduce.
- Increased Fitness: Organisms with beneficial traits are more likely to survive and pass on those traits to their offspring.
- Galápagos Finches: A prime example of natural selection in action, with beak size changing in response to seed availability.
- Peter and Rosemary Grant: Scientists who observed and studied Galapagos finch populations for decades, documenting natural selection.
Variation and Adaptation
- Variation: Differences among individuals within a population are essential for natural selection to occur.
- Genetic Basis: Variation must be based on genetic differences, not just environmental factors, for traits to be passed on.
- Adaptation: A heritable trait that provides an advantage for survival and reproduction in a specific environment.
- Acclimation: Temporary changes in phenotype due to environmental changes that are not passed on to offspring.
- Environmental Context: Favorable traits are dependent on the current environment, which can change, leading to different selective pressures.
Other Mechanisms of Evolution
- Mutation: The ultimate source of genetic variation, introducing new alleles into a population.
- Mutation Outcomes: Mutations can be harmful, beneficial, or neutral in terms of their effect on an organism's phenotype.
- Antibiotic Resistance: Bacteria can accumulate mutations rapidly, leading to resistance to antibiotics.
- Genetic Drift: Random changes in allele frequencies, especially prominent in small populations.
- Bottleneck Effect: A drastic reduction in population size due to random events, leading to a loss of genetic diversity.
- Founder Effect: A new population founded by a small group of individuals, potentially lacking the full genetic diversity of the original population.
- Gene Flow: The movement of alleles between populations through migration, increasing genetic diversity.
Patterns of Evolution
- Divergent Evolution: Two species evolve in different directions from a common ancestor.
- Convergent Evolution: Similar phenotypes evolve independently in different species.
- Analogous Structures: Similar structures in different species that evolved independently, serving similar functions.
- Homologous Structures: Structures shared by different species due to a common ancestor.
Speciation
- Biological Species Concept: A group of organisms that can interbreed and produce fertile offspring.
- Speciation: The formation of two new species from an original species.
- Allopatric Speciation: Speciation occurring due to geographic separation of populations.
- Sympatric Speciation: Speciation occurring within a parent species in the same geographical location.
Allopatric Speciation
- Geographic Isolation: Barriers prevent gene flow between populations, leading to the accumulation of genetic differences.
- Environmental Differences: Different selection pressures in isolated environments drive adaptation in different directions.
- Reproductive Isolation: Eventually, genetic differences become so great that populations can no longer interbreed, forming distinct species.
- Adaptive Radiation: Rapid speciation events from a single ancestral species, often occurring in isolated environments like islands.
Sympatric Speciation
- Divergent Evolution Without Isolation: The possibility of speciation without geographic separation.
- Genetic Mechanisms: Sympatric speciation can involve mechanisms like chromosomal changes or disruptive selection.
- Disruptive Selection: Selection favoring extreme phenotypes, potentially leading to the evolution of isolated breeding groups within a population.
Sympatric Speciation
- Sympatric speciation involves the formation of new species within the same geographic location.
- A scenario involving a fish population in a lake illustrates the process.
- Increased competition for food sources drives a group of fish to utilize an unused food source at a different depth in the lake.
- This leads to greater interaction and breeding among the fish utilizing the new food source.
- Over time, genetic differences accumulate, potentially leading to reproductive isolation and the formation of a new species.
- Lake Victoria in Africa showcases the phenomenon of sympatric speciation among cichlid fish.
- Researchers have documented hundreds of sympatric speciation events in cichlid fish, occurring in a short period of time.
- Figure 11 depicts sympatric speciation in cichlids in Nicaragua, with two distinct types adapting to different food sources despite sharing the same geographic location.
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Description
Explore the fundamental concepts of evolution through natural selection. Discover how limited resources lead to survival struggles, the significance of favorable traits, and the adaptation of species like the Galápagos finches. Understand the vital role of genetic variation in the evolutionary process.
