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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.

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...

Frequency-dependent Selection

Frequency-dependent Selection

When the fitness of a trait is influenced by how common it is (i.e., its frequency) relative to different traits within a population, this is referred to as frequency-dependent selection. Frequency-dependent selection may occur between species or within a single species. This type of selection can either be positive—with more common phenotypes having higher fitness—or negative, with rarer phenotypes conferring increased fitness.

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.

Limits to Natural Selection

Limits to Natural Selection

Organisms that are well-adapted to their environment are more likely to survive and reproduce. However, natural selection does not lead to perfectly adapted organisms. Several factors constrain natural selection.

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).

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Related Experiment Video

Updated: Jul 20, 2025

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

Coevolution of Patch Selection in Stochastic Environments.

Sebastian J Schreiber, Alexandru Hening, Dang H Nguyen

The American Naturalist

|August 2, 2023

Summary

This summary is machine-generated.

Environmental variability shapes species interactions and habitat selection. Coevolutionarily stable strategies (coESSs) reveal how species balance growth and risk, leading to bet-hedging strategies in changing landscapes.

Keywords:

coevolution environmental stochasticity evolutionarily stable strategy habitat selection portfolio theory

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Last Updated: Jul 20, 2025

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Area of Science:

Ecology
Evolutionary Biology
Theoretical Ecology

Background:

Species inhabit dynamic landscapes with varying environmental conditions.
Ideal free distributions explain some habitat selection but not all observed patterns, such as occupying sink patches or predator avoidance of productive areas.

Purpose of the Study:

To investigate coevolutionarily stable strategies (coESSs) for patch selection in multispecies systems.
To understand how spatial and temporal environmental heterogeneity influences species interactions and distributions.

Main Methods:

Developed and solved multispecies stochastic Lotka-Volterra models.
Analyzed coevolutionarily stable strategies (coESSs) for patch selection under environmental heterogeneity.
Applied principles from modern portfolio theory to interpret results.

Main Results:

At coESS, differences in local contributions to population growth rate mean and variance are equalized across occupied patches.
Environmental stochasticity can lead to novel enemy-free/victimless spaces and generate hydra effects.
CoESS often involves bet-hedging strategies, including the use of stochastic sink populations.

Conclusions:

Environmental stochasticity significantly alters evolutionary outcomes of species interactions and spatial distributions.
CoESS provides a framework to explain complex ecological patterns not captured by simpler models.
Understanding these dynamics is crucial for predicting species persistence in heterogeneous and changing environments.