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Types of Selection

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...

Mutation, Gene Flow, and Genetic Drift

Mutation, Gene Flow, and Genetic Drift

In a population that is not at Hardy-Weinberg equilibrium, the frequency of alleles changes over time. Therefore, any deviations from the five conditions of Hardy-Weinberg equilibrium can alter the genetic variation of a given population. Conditions that change the genetic variability of a population include mutations, natural selection, non-random mating, gene flow, and genetic drift (small population size).

Genetic Drift

Genetic Drift

Natural selection—probably the most well-known evolutionary mechanism—increases the prevalence of traits that enhance survival and reproduction. However, evolution does not merely propagate favorable traits, nor does it always benefit populations.

Natural Selection and Mating Preferences

Natural Selection and Mating Preferences

The principle of natural selection posits that organisms better adapted to their environment are more likely to survive and reproduce. This principle is closely intertwined with mating preferences, a key aspect of sexual selection, which evolutionary psychologists believe is driven by instincts to propagate one's genes. Such instincts significantly influence mating behaviors and preferences between genders.
Females, due to their biological roles in conception, pregnancy, and nursing, inherently...

Evolution of New Traits in Microbes

Evolution of New Traits in Microbes

Microorganisms evolve rapidly due to their large population sizes and short generation times, often exhibiting measurable changes within days under laboratory conditions. Natural selection acts on standing genetic variation, enabling the retention and amplification of beneficial traits that confer fitness advantages in changing environments.Adaptive Pigment Regulation in RhodobacterIn Rhodobacter, a genus of purple non-sulfur bacteria, light-harvesting pigments such as bacteriochlorophyll and...

What is Natural Selection?

What is Natural Selection?

Natural selection is an evolutionary process in which individuals with survival-promoting traits reproduce at higher rates. These favorable traits become more common within a population or species. Naturally selected traits initially arise via random genetic mutations. In order for selection to occur, there must be variation within a population, the trait controlling the variation must be heritable, and there must be an evolutionary advantage for variation in the trait.

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Related Experiment Video

Updated: May 21, 2026

Following the Dynamics of Structural Variants in Experimentally Evolved Populations

Following the Dynamics of Structural Variants in Experimentally Evolved Populations

Published on: February 3, 2023

Dynamic mutation-selection balance as an evolutionary attractor.

Sidhartha Goyal¹, Daniel J Balick, Elizabeth R Jerison

¹Kavli Institute for Theoretical Physics, Department of Physics, University of California, Santa Barbara, CA 93106, USA.

|June 5, 2012

Summary

This summary is machine-generated.

Asexual populations can remain stable despite deleterious mutations thanks to beneficial mutations. A low fraction of beneficial mutations is sufficient to counteract Muller's ratchet and maintain population fitness.

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Area of Science:

Evolutionary biology
Population genetics

Background:

Deleterious mutations accumulate in asexual populations due to Muller's ratchet, potentially degrading fitness.
Purifying selection alone is insufficient to prevent this accumulation in finite populations.

Purpose of the Study:

To investigate the conditions under which asexual populations can maintain long-term stability.
To determine the required influx of beneficial mutations to offset deleterious mutation accumulation.

Main Methods:

Theoretical modeling of mutation-selection balance in asexual populations.
Calculation of the critical fraction of beneficial mutations (ε) for population stability.

Main Results:

A dynamic mutation-selection balance can maintain population fitness.
A surprisingly low fraction of beneficial mutations (ε) is sufficient for stability, even with high mutation rates and weak selection.
This mechanism can operate in small populations.

Conclusions:

Beneficial mutations are crucial for the long-term evolutionary stability of asexual populations.
The influx of beneficial mutations can counteract Muller's ratchet, preventing fitness degradation.
This model may explain the persistence of asexual genomes like mitochondria.