Adaptive Molecular Evolution in Population Genetics

Adaptive molecular evolution examines the genetic changes that improve organismal fitness and become established within populations under natural selection. This field integrates theoretical frameworks such as the nearly neutral theory, models of the distribution of fitness effects and coalescent approaches, with empirical genomic data to identify beneficial substitutions, selective sweeps and the interplay of selection with genetic drift. Advances in high-throughput sequencing and statistical inference have enabled the quantification of selection coefficients, the rate of adaptive amino-acid substitutions and the genomic architecture of adaptation across diverse taxa. Central to this discipline are concepts of effective population size, linkage disequilibrium and the site-frequency spectrum, which together determine the efficacy of selection and the signature it leaves on patterns of genetic diversity. Insights into adaptive evolution inform our understanding of disease susceptibility, resistance to pathogens, responses to environmental change and the optimisation of breeding programmes for agriculture and conservation.

Research from Nature Portfolio

One study in Nature Communications has revealed that genetic diversity in European butterflies is shaped both by long-term population size and by the impact of selection at linked sites. By comparing genome-wide polymorphism across 38 species, researchers demonstrated that smaller body size and longer recombination maps correlate with elevated neutral diversity, indicating that species with greater recombination experience reduced interference from linked selection. These findings underscore how life-history traits interact with genome structure to modulate the balance between drift and adaptation, and they provide a framework for predicting the capacity of wild populations to respond to environmental pressures.

Research from all publishers

A new Python-based toolkit offers rapid inference of the distribution of fitness effects from large site-frequency spectra. This software integrates flexible modelling of genomic covariates, efficient parsing of variant‐call data and joint inference across multiple categories of mutations, greatly accelerating studies of adaptive and deleterious variation in non-model organisms. Another investigation into mammalian populations has quantified the proportion of beneficial mutations that restore previously lost fitness rather than confer novel adaptation. By reconstructing shared fitness landscapes across 87 mammalian species, it was shown that 15–45 per cent of ongoing positive selection reflects non-adaptive reversions, highlighting a dynamic equilibrium of damage and restoration within genomes. A conceptual review of the neutralist–selectionist debate has clarified the distinctions between strict neutrality, the original neutral theory, the nearly neutral hypothesis and panselectionist interpretations. By dissecting the assumptions underlying tests of neutrality and selection, it proposes refined definitions to sharpen empirical contrasts and to guide future studies in estimating the true proportion of adaptive substitutions.

Adaptive Molecular Evolution in Population Genetics publication trend

The graph below shows the total number of articles in adaptive molecular evolution in population genetics across all publications each year (not limited to Nature Index journals).

Technical terms

Effective population size (Nₑ): The size of an idealised population that experiences the same genetic drift as the actual population, determining the efficiency of selection.

Distribution of fitness effects (DFE): The spectrum of selective advantages and disadvantages associated with new mutations in a population.

Site-frequency spectrum (SFS): The distribution of allele frequencies at polymorphic sites, used to infer demographic history and selection.

Selectively swept region: A genomic segment where a beneficial allele has rapidly increased in frequency, reducing neighbouring variation.

Nearly neutral theory: An extension of the neutral theory positing that many mutations have very small fitness effects and may fix by drift or weak selection.

Linkage disequilibrium: The non-random association of alleles at different loci, influenced by recombination and selection.

References

1. The determinants of genetic diversity in butterflies. Nature Communications (2019).
2. fastDFE: Fast and Flexible Inference of the Distribution of Fitness Effects. Molecular Biology and Evolution (2024).
3. Estimating the proportion of beneficial mutations that are not adaptive in mammals. PLOS Genetics (2024).
4. Moderating the neutralist–selectionist debate: exactly which propositions are we debating, and which arguments are valid?. Biological Reviews (2023).