Name: natural selection patterns in populations
Uploaded: 2026-06-01T06:28:25.996Z
Duration: 1 min 46 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Biology

Biological Evolution- Unity and Diversity

LS.Bio.9.1

Types of Selection

Natural selection changes the frequencies of particular alleles and phenotypes within a population through directional, stabilizing, and disruptive selection.In a typical population, most individuals have intermediate traits, while a few individuals have extreme traits. In directional selection, environmental or sexual pressures favor one extreme phenotype, causing the population mean to shift toward that trait.Imagine a population of lizards living on an island with no competitors or predators.In this population, females prefer bright, colorful, and fit males. This preference is called sexual selection.As females mate more often with bright, colorful males, the frequency of this phenotype increases. Over time, the population shifts toward the bright phenotype. This is directional selection.Now, consider a different situation. A predator arrives on the island, and bright, colorful males become easy prey.At the same time, dull males survive but attract few females.Because both extremes face disadvantages, males with intermediate color survive and reproduce more successfully. This is called stabilizing selection.The last type of selection is disruptive selection, in which both extreme phenotypes are favored, and the intermediate phenotype is selected against.In this lizard population, females prefer bright males, so these males mate more often.At the same time, dull males that look similar to females avoid aggression from dominant males and gain mating opportunities without direct competition. Intermediate males do not have either advantage.Because both bright and dull males reproduce successfully, their frequencies increase, while the frequency of intermediate males decrease.

types of selection

Natural selection influences the frequencies of particular alleles and phenotypes within populations in several different ways. Primarily, natural selection can be directional, stabilizing, or disruptive. Directional selection favors one extreme trait and shifts the population towards that phenotype while selecting against individuals displaying alternate traits. Stabilizing selection favors an intermediate trait with a narrow range of variation. Deviation from the optimal phenotype towards an extreme one is unfavorable. Finally, disruptive selection favors both extremes of a phenotype, while intermediate phenotypes are selected against.<h4>Directional Selection</h4>Directional selection favors one extreme of a phenotype. For example, in sockeye salmon, research has shown that directional selection is favoring seasonally earlier migration. This is thought to be due to predation pressure from fisheries, as fishing increases later in the migration season. Thus, fish arriving and spawning earlier may have a better chance of reaching their destination to reproduce before being caught by fishermen.<h4>Stabilizing Selection</h4>When a particular non-extreme phenotype is favored, this is referred to as stabilizing selection. For example, across many species of birds, clutch size (the number of eggs in a single brood) is kept within an optimal window. Lapwings and golden plovers typically lay four eggs. This optimization is a trade-off between keeping the clutch size low enough to ensure enough resources to feed all the chicks and having enough chicks to ensure that at least some survive to adulthood. This is a common theme among bird species.<h4>Disruptive Selection</h4>In some scenarios, two extremes of a trait may be more favorable in the environment than an intermediate trait. The African black-bellied seedcracker (Pyrenestes ostrinus) displays an impressive polymorphism for beak size that is not determined by sex, body size, age or geographic origin. Two major distinct morphs exist, small-billed and large-billed. This trait is controlled by a single autosomal locus, with large bills being dominant. These two distinct bill morphologies allow the seedcrackers to easily eat the seeds of different sedge grasses. The small-billed seedcrackers primarily eat sedge species with softer seeds, whereas the large-billed birds can crack the harder seeds of other species of sedge. However, birds with bills of intermediate sizes cannot easily eat either type and are thus rarely seen.

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Education

JoVE Core

Evolution

Natural Selection

KEY TERMS AND CONCEPTS

Learn by watching this video about Types of Selection: Natural vs Artificial Selection at JoVE.com

natural selection patterns in populations

Natural selection can change how alleles and traits appear in a population. The main patterns are directional selection, stabilizing selection, and disruptive selection. Each pattern favors a different range of phenotypes, or observable traits.

Directional selection favors one extreme of a trait. In sockeye salmon, selection appears to favor earlier migration in the season. Later in the migration season, fishing pressure is higher. Fish that arrive and spawn earlier may have a better chance to reproduce before being caught.

Stabilizing selection favors an intermediate trait. A common example is clutch size, which is the number of eggs in one brood. Many bird species, including lapwings and golden plovers, typically lay four eggs. This number seems to balance the need for enough chicks with the need to provide enough resources for them.

Disruptive selection favors both extremes of a trait while against the intermediate form. The African black-bellied seedcracker shows this pattern in beak size. Small-billed birds eat softer sedge seeds, and large-billed birds crack harder seeds. Birds with intermediate bills do not feed well on either seed type, so they are seen less often.

Natural Selection Patterns in Populations

natural-selection-patterns-in-populations

what is natural selection?

Natural Selection and Adaptive Evolution

Natural selection is an evolutionary process that changes populations over time. Individuals with traits that help them survive and reproduce tend to leave more offspring. As those favorable traits are passed on, they become more common in the population or species. These helpful traits usually begin with random genetic mutations. Natural selection can act only when a population shows variation, the trait is heritable, and the variation gives an evolutionary advantage. In other words, the...

Natural selection can change how alleles and traits appear in a population. The main patterns are directional selection, stabilizing selection, and disruptive selection. Each pattern favors a different range of phenotypes, or observable traits. Directional selection favors one extreme of a trait. In sockeye salmon, selection appears to favor earlier migration in the season. Later in the migration season, fishing pressure is higher. Fish that arrive and spawn earlier may have a better chance to...

frequency-dependent selection

Common vs Rare Trait Selection

Common vs rare trait selection describes how a trait’s fitness can change based on how often it appears in a population. This process is called frequency-dependent selection. It can happen between species or within a single species. The effect may be positive, where common phenotypes do better, or negative, where rare phenotypes do better. Positive frequency-dependent selection gives an advantage to the most common phenotype. This is often seen in mimicry systems. In Central America,...

limits to natural selection

Why Natural Selection Has Limits

Natural selection has limits, even when a trait would seem helpful. Organisms that fit their environment better are more likely to survive and reproduce. But evolution does not always produce perfectly adapted organisms. One limit is that natural selection can only work with genetic variation that already exists. For example, red tusks might help elephants by discouraging ivory-seeking poachers. If no allele, or gene variant, for red tusks is present, natural selection cannot raise its...

key terms and concepts

Explore directional, stabilizing, and disruptive selection with real examples from salmon, birds, and seedcrackers. Learn how natural selection shapes populations.

Natural Selection Patterns in Populations | JoVE K12

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biology

LS.Bio.9.3

Pennsylvania State Academic Standards

Life Science

Natural Selection and Evolution

3.1.9-12.T

3.1.9-12.U

3.1.9-12.W

Louisiana Student Standards for Science

High School

Life Sciences

Biological Evolution: Unity And Diversity

HS-LS4-2

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Mechanisms

Virginia  Standards of Learning

HIgh School

BIO.7

BIO.7.c

LS.11

LS.11.a

LS.11.c

Minnesota Academic Standards in Science

3.2.1 9L.3.2.1.3

new-jersey-student-learning-standards-for-science

New Jersey Student Learning Standards for Science

Biological Evolution: Unity and Diversity

HS-LS4-4

Arizona Science Standards

HS+B.L4

HS+B.L4U1.14

Alabama Course of Study Science

Unity and Diversity

9-12.B.4.14

Next Generation Science Standards

heredity-inheritance-and-variation-of-traits

Heredity: Inheritance and Variation of Traits

HS-LS3-3

HS-LS4-3

HS-LS4-5

Florida Department of Education

SC.912.L.15

SC.912.L.15.13

Texas Essential Knowledge and Skills

BIO.10

BIO.10.A

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

B-LS4-2.

B-LS4-3.

B-LS4-4.

new-york-state-science-learning-standards

New York State Science Learning Standards

Inheritance and Variation of Traits

HS-LS3-3.

HS-LS4-3.

HS-LS4-4.

Georgia Standards of Excellence

Ecology

SEC2.

SEC2.c

SB6.d

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Natural selection influences the frequencies of particular alleles and phenotypes within populations in several different ways. Primarily, natural ...

Frequency-dependent Selection

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Limits to Natural Selection

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Convergent Evolution

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LS.Bio.9.2

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LS.Bio.9.4

Extinction

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LS.Bio.10.1

Synteny and Evolution

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Use models (including dichotomous keys, scientific nomenclature, cladograms, phylogenetic trees) to identify organisms and exemplify relationships.

LS.Bio.10.2

Understand natural selection as a mechanism for biological evolution.

Natural Selection Patterns in Populations

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