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.

Martin, Ryan A, et David W Pfennig. « La sélection perturbatrice généralisée dans la nature est associée à une concurrence intense pour les ressources. » BMC Evolutionary Biology 12 (2 août 2012) : 136. [<a href="https://doi.org/10.1186/1471-2148-12-136 » target="__blank">Source</a>]

Podos, Jeffrey et Stephen Nowicki. « Becs, adaptation et évolution vocale chez les pinsons de Darwin ». BioScience 54, n° 6 (1er juin 2004) : 501-10. [<a href="https ://doi.org/10.1641/0006-3568(2004)054%5B0501 :BAAVEI %5D2.0.CO ;2 » target="__blank">Source</a>]

types de sélection

La s&#xE9;lection naturelle influence les fr&#xE9;quences d&#x2019;all&#xE8;les et de ph&#xE9;notypes particuliers au sein des populations de plusieurs fa&#xE7;ons diff&#xE9;rentes. Principalement, la s&#xE9;lection naturelle peut &#xEA;tre directionnelle, stabilisatrice ou perturbatrice. La s&#xE9;lection directionnelle favorise un trait extr&#xEA;me et d&#xE9;place la population vers ce ph&#xE9;notype tout en ne s&#xE9;lectionnant pas les individus affichant des traits alternatifs. La s&#xE9;lection stabilisatrice favorise un trait interm&#xE9;diaire avec une gamme &#xE9;troite de variation. L&#x2019;&#xE9;cart du ph&#xE9;notype optimal vers un ph&#xE9;notype extr&#xEA;me est d&#xE9;favorable. Enfin, la s&#xE9;lection perturbatrice favorise les deux extr&#xEA;mes d&#x2019;un ph&#xE9;notype, tandis que les ph&#xE9;notypes interm&#xE9;diaires ne sont pas s&#xE9;lectionn&#xE9;s.
 
 <h4>S&#xE9;lection directionnelle</h4>
 
 La s&#xE9;lection directionnelle favorise une extr&#xEA;me d&#x2019;un ph&#xE9;notype. Par exemple, chez le saumon rouge, la recherche a montr&#xE9; que la s&#xE9;lection directionnelle favorise la migration saisonni&#xE8;re plus pr&#xE9;coce. On pense que cela est d&#xFB; &#xE0; la pression de pr&#xE9;dation exerc&#xE9;e par l&#x2019;industrie de la p&#xEA;che car la p&#xEA;che augmente plus tard dans la saison de migration. Ainsi, les poissons qui arrivent et pondent plus t&#xF4;t peuvent avoir de meilleures chances d&#x2019;atteindre leur destination pour se reproduire avant d&#x2019;&#xEA;tre captur&#xE9;s par les p&#xEA;cheurs.
 
 <h4>S&#xE9;lection stabilisatrice</h4>
 
 Lorsqu&#x2019;un ph&#xE9;notype non extr&#xEA;me particulier est favoris&#xE9;, c&#x2019;est ce qu&#x2019;on appelle la s&#xE9;lection stabilisatrice. Par exemple, dans de nombreuses esp&#xE8;ces d&#x2019;oiseaux, la taille de la couv&#xE9;e (le nombre d&#x2019;&#x153;ufs dans une seule couv&#xE9;e) est conserv&#xE9;e dans un cr&#xE9;neau optimal. Les vanneaux et les pluviers dor&#xE9;s pondent g&#xE9;n&#xE9;ralement quatre &#x153;ufs. Cette optimisation est un compromis entre maintenir la taille de la couv&#xE9;e assez r&#xE9;duite afin d&#x2019;assurer suffisamment de ressources pour nourrir tous les poussins et avoir assez de poussins pour s&#x2019;assurer qu&#x2019;au moins certains survivent &#xE0; l&#x2019;&#xE2;ge adulte. C&#x2019;est un th&#xE8;me commun parmi les esp&#xE8;ces d&#x2019;oiseaux.
 
 <h4>S&#xE9;lection perturbatrice</h4>
 
 Dans certains sc&#xE9;narios, deux extr&#xEA;mes d&#x2019;un trait peuvent &#xEA;tre plus favorables dans l&#x2019;environnement qu&#x2019;un trait interm&#xE9;diaire. Le pyr&#xE9;neste ponceau (Pyrenestes ostrinus) pr&#xE9;sente un polymorphisme impressionnant pour la taille du bec qui n&#x2019;est d&#xE9;termin&#xE9; ni par le sexe, ni par la taille du corps, ni par l&#x2019;&#xE2;ge ni par l&#x2019;origine g&#xE9;ographique. Il existe deux morphologies distinctes majeures, &#xE0; petit bec et &#xE0; grand bec. Ce trait est contr&#xF4;l&#xE9; par un seul locus autosomique, les grands becs &#xE9;tant dominants. Ces deux morphologies distinctes du bec permettent au pyr&#xE9;neste ponceau de manger facilement les graines de diff&#xE9;rents carex. Les pyr&#xE9;nestes ponceaux &#xE0; petit bec mangent principalement des esp&#xE8;ces de carex avec des graines plus molles, tandis que les oiseaux &#xE0; gros bec peuvent casser les graines plus dures d&#x2019;autres esp&#xE8;ces de carex. Cependant, les oiseaux avec des becs de tailles interm&#xE9;diaires ne peuvent manger facilement ni l&#x2019;un ni l&#x2019;autre type de graines et donc on ne les voit pas souvent.

Types de sélection

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

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Education

Enseignement

JoVE Core

Biologie

Evolution

Évolution

Natural Selection

La sélection naturelle

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

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...

types of selection

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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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

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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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LS.Bio.9.2

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LS.Bio.9.4

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LS.Bio.10.1

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LS.Bio.10.2

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Natural Selection Patterns in Populations

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