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What is Natural Selection?

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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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Updated: Feb 15, 2026

Human Colonoid Monolayers to Study Interactions Between Pathogens, Commensals, and Host Intestinal Epithelium

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Immunogenetic novelty confers a selective advantage in host-pathogen coevolution.

Karl P Phillips^1,2, Joanne Cable³, Ryan S Mohammed⁴

¹Evolutionary Biology Group, Faculty of Biology, Adam Mickiewicz University, 60-614 Poznań, Poland.

Proceedings of the National Academy of Sciences of the United States of America

|January 18, 2018

Summary

Novel immune gene variants (MHC) enhance host resistance to parasites. This study experimentally confirms that new major histocompatibility complex (MHC) variants provide guppies with significant protection against infection, supporting evolutionary theories.

Keywords:

Poecilia reticulata Red Queen coevolution frequency-dependent selection host–pathogen coevolution major histocompatibility complex

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Published on: July 10, 2021

Area of Science:

Immunology
Evolutionary Biology
Genetics

Background:

The Major Histocompatibility Complex (MHC) is a highly polymorphic gene family vital for vertebrate adaptive immunity.
High MHC diversity is theorized to result from pathogen-driven selection, where novel MHC alleles confer resistance.
The
Red Queen
coevolutionary hypothesis predicts novel MHC variants enhance host defense, but empirical evidence is limited.

Purpose of the Study:

To experimentally test if novel MHC variants (alleles and supertypes) increase resistance in guppies (Poecilia reticulata) against the ectoparasite Gyrodactylus turnbulli.
To investigate the role of immunogenetic novelty in host-pathogen interactions within a naturalistic context.

Main Methods:

Utilized controlled infection trials with wild-sourced Gyrodactylus parasites.
Employed F2 hybrid guppy populations, derived from crosses of wild populations, to assess resistance to novel MHC variants.
Quantified infection intensity in hosts exposed to parasites and specific MHC variants.

Main Results:

Hosts possessing novel MHC variants (alleles or supertypes) exhibited a 35-37% reduction in infection intensity.
The number of MHC variants an individual carried (MHC diversity) was not a significant predictor of resistance.
Direct experimental evidence supports the advantage of novel MHC variants in conferring parasite resistance.

Conclusions:

Novel MHC variants provide a significant advantage in host resistance against parasitic infections.
This finding provides direct empirical support for the role of immunogenetic novelty in driving MHC polymorphism and host-pathogen coevolution.
Highlights the importance of novel immune gene variants in maintaining host-parasite equilibrium.