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Natural Selection and Adaptation

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Natural selection, a fundamental concept in evolutionary biology, is the mechanism by which evolution is driven, favoring organisms that are best adapted to their environments. This process enhances their chances of survival and reproduction. Adaptation, a key outcome of this process, involves genetic modifications that optimize an organism's functionality under specific environmental challenges, such as extreme cold or thinner air at high altitudes.
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When more than one gene is responsible for a given phenotype, the trait is considered polygenic. Human height is a polygenic trait. Studies have uncovered hundreds of loci that influence height, and there are believed to be many more. Due to the high number of genes involved, as well as environmental and nutritional factors, height varies significantly within a given population. The distribution of height forms a bell-shaped curve, with relatively few individuals in the population at the...

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Hardy-Weinberg Principle

Hardy-Weinberg Principle

Diploid organisms have two alleles of each gene, one from each parent, in their somatic cells. Therefore, each individual contributes two alleles to the gene pool of the population. The gene pool of a population is the sum of every allele of all genes within that population and has some degree of variation. Genetic variation is typically expressed as a relative frequency, which is the percentage of the total population that has a given allele, genotype or phenotype.

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Related Experiment Video

Updated: Aug 11, 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

Polygenic adaptation dynamics in large, finite populations.

Archana Devi¹, Kavita Jain²

¹Biodesign Center for Mechanisms of Evolution, Arizona State University, Tempe, AZ 85287, USA.

Biorxiv : the Preprint Server for Biology

|February 7, 2023

Summary

Finite populations enhance genetic sweeps during adaptation. Even small environmental changes can drive allele frequencies rapidly at large-effect loci, unlike in infinite populations.

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Area of Science:

Evolutionary genetics
Population genetics theory

Background:

Understanding polygenic trait adaptation to environmental change is crucial.
Previous models often assumed infinite population sizes, limiting applicability.

Approach:

Utilized diffusion theory to model adaptation dynamics in large, finite populations.
Analyzed steady-state allele frequency distributions under stabilizing selection and mutation.
Investigated adaptation following sudden shifts in the phenotypic optimum.

Key Points:

Stationary allele frequency distributions are unimodal for small effect sizes and bimodal for large effect sizes, mirroring deterministic predictions.
Finite population size significantly increases the probability of selective sweeps at large-effect loci.
Adaptation can occur rapidly, with large-effect alleles reaching high frequencies quickly, even with minor environmental shifts.

Conclusions:

Finite population size plays a critical role in the speed and mechanism of polygenic adaptation.
Stochastic effects in finite populations can lead to rapid adaptation via selective sweeps, contrary to infinite population predictions.