Natural selection
53 flashcards covering Natural selection for the MCAT Biology & Biochemistry section.
Natural selection is a fundamental process in evolution where certain traits become more common in a population over time because they improve an organism's chances of survival and reproduction. Imagine a group of finches on an island: those with beaks better suited to available food sources are more likely to thrive and have offspring, gradually shifting the population's characteristics. This mechanism, first described by Charles Darwin, explains the diversity of life and how species adapt to their environments, making it a cornerstone of biology.
On the MCAT, natural selection frequently appears in Biology and Biochemistry questions that assess your grasp of evolutionary concepts, such as identifying mechanisms, analyzing adaptations, or evaluating evidence from fossils and genetics. Common traps include mistaking it for random processes like genetic drift or overlooking environmental factors, so focus on key elements like variation, heritability, and selection pressures. Mastering real-world applications, like antibiotic resistance, will help you tackle passage-based and standalone questions effectively.
A concrete tip: Practice distinguishing natural selection from other evolutionary forces by applying it to simple scenarios.
Terms (53)
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Natural selection
Natural selection is the mechanism of evolution where individuals with traits that enhance survival and reproduction in their environment are more likely to pass those traits to the next generation, leading to changes in population characteristics over time.
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Charles Darwin
Charles Darwin was a naturalist whose theory of evolution by natural selection, detailed in his book On the Origin of Species, proposed that species evolve through the differential survival and reproduction of individuals with advantageous variations.
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Alfred Russel Wallace
Alfred Russel Wallace was a naturalist who independently developed the theory of evolution by natural selection, similar to Darwin, and contributed evidence from his studies in the Malay Archipelago.
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Adaptation
An adaptation is a heritable trait that increases an organism's fitness in its environment, resulting from natural selection acting on genetic variations over generations.
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Fitness
In evolutionary terms, fitness refers to the ability of an organism to survive and reproduce in its environment, measured by the number of offspring that survive to reproduce themselves.
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Genetic variation
Genetic variation is the diversity in DNA sequences among individuals in a population, providing the raw material for natural selection to act upon and drive evolutionary change.
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Mutation
A mutation is a change in an organism's DNA sequence, which can introduce new genetic variation that natural selection may favor or eliminate based on its effects on survival and reproduction.
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Gene flow
Gene flow is the transfer of genetic material between populations through migration, which can introduce new variations and influence the course of natural selection in those populations.
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Genetic drift
Genetic drift is the random change in allele frequencies in a population due to chance events, which can lead to the loss of genetic variation and is distinct from natural selection as it is not driven by environmental pressures.
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Directional selection
Directional selection is a type of natural selection that favors individuals at one extreme of a trait's variation, shifting the population's average trait value over generations.
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Stabilizing selection
Stabilizing selection is natural selection that favors individuals with intermediate traits, reducing variation in the population by selecting against extremes.
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Disruptive selection
Disruptive selection is natural selection that favors individuals at both extremes of a trait's variation, potentially leading to the splitting of a population into distinct groups.
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Sexual selection
Sexual selection is a form of natural selection driven by competition for mates, where traits that enhance an individual's ability to attract mates or compete for them become more common.
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Artificial selection
Artificial selection is the process by which humans selectively breed organisms for desired traits, demonstrating principles of natural selection but under human control.
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Speciation
Speciation is the process by which one species evolves into two or more distinct species, often driven by natural selection acting on populations in different environments.
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Allopatric speciation
Allopatric speciation occurs when a population is divided by a geographical barrier, allowing natural selection and genetic drift to cause divergence into new species.
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Sympatric speciation
Sympatric speciation is the evolution of new species from a single ancestral population in the same geographical area, often due to natural selection creating reproductive isolation.
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Reproductive isolation
Reproductive isolation is a key outcome of natural selection that prevents interbreeding between populations, leading to the formation of new species.
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Hardy-Weinberg principle
The Hardy-Weinberg principle states that in a large, randomly mating population with no evolutionary forces like natural selection, allele frequencies remain constant across generations.
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Allele frequency
Allele frequency is the proportion of a specific allele in a population's gene pool, which natural selection can alter by favoring certain alleles over others.
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Genotype frequency
Genotype frequency is the proportion of individuals in a population with a particular genetic combination, which can be influenced by natural selection acting on phenotypes.
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Conditions for Hardy-Weinberg equilibrium
The conditions for Hardy-Weinberg equilibrium include no mutations, no gene flow, large population size, random mating, and no natural selection, allowing allele frequencies to remain stable.
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Fossil evidence for evolution
Fossil evidence supports evolution by natural selection through the discovery of transitional forms that show gradual changes in species over geological time.
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Vestigial structures
Vestigial structures are remnants of organs or features that were functional in ancestors but are reduced or useless in modern species, evidence of evolution by natural selection.
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Homologous structures
Homologous structures are features in different species that share a common ancestry, demonstrating how natural selection can modify traits for different functions.
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Analogous structures
Analogous structures are features in different species that serve similar functions but evolved independently, often due to similar environmental pressures from natural selection.
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Convergent evolution
Convergent evolution is when unrelated species develop similar traits due to natural selection in similar environments, even without a common ancestor.
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Divergent evolution
Divergent evolution occurs when populations of a species become distinct due to natural selection in different environments, leading to new species.
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Adaptive radiation
Adaptive radiation is a rapid diversification of a single ancestral species into multiple forms, driven by natural selection in varying ecological niches.
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Bottleneck effect
The bottleneck effect is a type of genetic drift where a population is drastically reduced, potentially altering allele frequencies in ways unrelated to natural selection.
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Founder effect
The founder effect occurs when a small group from a larger population establishes a new one, leading to reduced genetic variation that natural selection then acts upon.
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Polymorphism
Polymorphism is the occurrence of two or more distinct forms of a trait in a population, maintained by natural selection if the forms provide advantages in different contexts.
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Balanced polymorphism
Balanced polymorphism is when multiple alleles for a gene are maintained in a population because natural selection favors heterozygotes, as in sickle cell trait conferring malaria resistance.
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Sickle cell anemia and selection
In regions with malaria, natural selection favors the sickle cell allele in heterozygotes, as it provides resistance to the disease, demonstrating balanced polymorphism.
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Peppered moth example
The peppered moth's color shift during the Industrial Revolution exemplifies natural selection, as darker moths survived better on soot-covered trees, increasing their frequency.
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Antibiotic resistance
Antibiotic resistance arises through natural selection, where bacteria with mutations allowing them to survive antibiotics reproduce, leading to resistant populations.
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Pesticide resistance
Pesticide resistance in insects results from natural selection favoring individuals with genetic variations that allow them to withstand pesticides, reducing the chemicals' effectiveness over time.
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Misconception: Survival of the fittest
The phrase 'survival of the fittest' is often misunderstood; in natural selection, it means reproductive success, not physical strength, and includes any advantageous trait.
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Role of environment in selection
The environment shapes natural selection by determining which traits confer a survival advantage, as changing conditions can favor different variations over time.
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Differential reproduction
Differential reproduction is the core of natural selection, where individuals with certain traits produce more offspring, passing those traits to future generations.
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Heritable traits
Heritable traits are genetic characteristics that can be passed to offspring, and natural selection acts on them to favor those that improve survival and reproduction.
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Non-heritable traits
Non-heritable traits, like those acquired during an organism's lifetime, are not influenced by natural selection because they cannot be passed to offspring.
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Evolutionary arms race
An evolutionary arms race is a cycle of natural selection where predators and prey continually adapt to each other, leading to escalating defenses and attacks.
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Co-evolution
Co-evolution is when two species reciprocally influence each other's evolution through natural selection, such as flowers and their pollinators developing mutual adaptations.
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Punctuated equilibrium
Punctuated equilibrium is a model of evolution suggesting that species experience long periods of stability interrupted by rapid changes due to intense natural selection.
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Microevolution
Microevolution refers to small-scale changes in allele frequencies within a population over a short period, driven by processes like natural selection.
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Macroevolution
Macroevolution involves large-scale evolutionary changes leading to new species or higher taxonomic groups, often resulting from extended natural selection.
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Population genetics
Population genetics studies how allele frequencies change over time, with natural selection being a key factor that can shift these frequencies based on environmental pressures.
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Selection pressure
Selection pressure is any factor in the environment that influences which traits are advantageous, driving natural selection by favoring certain genetic variations.
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Neutral selection
Neutral selection refers to genetic changes that are not affected by natural selection, as they neither help nor harm an organism's fitness.
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Evidence from biogeography
Biogeography provides evidence for natural selection by showing how species distributions correlate with environmental factors and historical events.
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Comparative anatomy
Comparative anatomy supports natural selection by revealing patterns like homologous structures that indicate common ancestry and adaptive modifications.
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Molecular evidence for evolution
Molecular evidence, such as DNA similarities between species, supports natural selection by showing how genetic changes accumulate over time.