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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.

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.

Background and Environment Affect Phenotype

Background and Environment Affect Phenotype

Although the genetic makeup of an organism plays a major role in determining the phenotype, there are also several environmental factors, such as temperature, oxygen availability, presence of mutagens, that can alter an organism’s phenotype.
An example of how genetic background affects phenotype can be seen in horses. The Extension gene in horses is responsible for their coat color. A wild-type gene (EE) produces black pigment in the coat, while a mutant gene (ee) produces red pigment. A...

Law of Segregation

Law of Segregation

When crossing pea plants, Mendel noticed that one of the parental traits would sometimes disappear in the first generation of offspring, called the F1 generation, and could reappear in the next generation (F2). He concluded that one of the traits must be dominant over the other, thereby causing masking of one trait in the F1 generation. When he crossed the F1 plants, he found that 75% of the offspring in the F2 generation had the dominant phenotype, while 25% had the recessive phenotype.

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.

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Related Experiment Video

Updated: Mar 29, 2026

Probing the Limits of Egg Recognition Using Egg Rejection Experiments Along Phenotypic Gradients

Probing the Limits of Egg Recognition Using Egg Rejection Experiments Along Phenotypic Gradients

Published on: August 22, 2018

Forbidden phenotypes and the limits of evolution.

Geerat J Vermeij¹

¹Department of Earth and Planetary Sciences , University of California , Davis, CA , USA.

Interface Focus

|December 8, 2015

Summary

This summary is machine-generated.

Evolutionary limits are not absolute. Natural selection overcomes constraints, driven by adaptive versatility and new ecological opportunities, leading to cumulative diversification over time.

Keywords:

evolution limits metabolism natural selection phenotypes

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Last Updated: Mar 29, 2026

Probing the Limits of Egg Recognition Using Egg Rejection Experiments Along Phenotypic Gradients

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Area of Science:

Evolutionary biology
Developmental biology
Ecology

Background:

Organismal diversity arises from evolution, but evolutionary paths may be constrained.
Understanding these constraints and how they change over time is key to evolutionary biology.

Purpose of the Study:

To review models explaining existing biological diversity.
To explore limitations in the evolutionary tree and how they are overcome.
To analyze the role of phenotypic constraints in eukaryotic evolution.

Main Methods:

Review of models for evolutionary diversity.
Analysis of 32 "forbidden states" (phenotypic limitations) in eukaryotes across habitats.
Examination of constraints related to time-energy budgets, development, and phylogeny.

Main Results:

No phenotypic constraint is absolute; most reflect limited time-energy budgets.
Natural selection imposes and overcomes constraints, including developmental and phylogenetic ones.
Increased adaptive versatility and ecological opportunities have removed many constraints over evolutionary time.
Phenotypes inaccessible in the Early Palaeozoic have evolved later; few adaptive states have disappeared.

Conclusions:

Evolutionary constraints are dynamic and surmountable.
The filling of phenotypic space is a cumulative process.
Diversification occurs in overlapping phases: biochemical, morphological, and cultural.