Sex reduces genetic variation: a multidisciplinary review

Area of Science:

• Evolutionary Biology
• Genetics

Background:

• The prevailing biological paradigm posits that sexual reproduction invariably increases genetic variation, a cornerstone of eukaryotic evolution and adaptation.
• However, significant evidence suggests sex often decreases genetic variation, a view supported by renowned biologists and observed across diverse fields.

Purpose of the Study:

• To challenge the established paradigm by presenting evidence that sexual reproduction decreases genetic variation.
• To explore the mechanisms by which sex acts as a filter, constraining genomic and epigenetic variation and potentially limiting adaptive evolution.

Main Methods:

• Review of evidence from ecology, paleontology, population genetics, and cancer biology.
• Analysis of the 'coarse filter' model where sex permits minor variations (nucleotide/gene level) but eliminates major ones (chromosomal rearrangements).

Main Results:

• Sex functions as a selective sieve, removing deleterious major genomic alterations while allowing neutral minor variations to persist.
• This filtering process constrains both genomic and epigenetic variation, thereby acting as a potential brake on adaptive evolution.

Conclusions:

• The reduction of genetic variation by sex, particularly at the genomic level, may offer benefits that outweigh the recognized costs of sexual reproduction.
• Sex's role in limiting variation and slowing evolution provides a new perspective on its evolutionary significance.