Paradox of Sex
- LAST REVIEWED: 10 August 2020
- LAST MODIFIED: 29 November 2018
- DOI: 10.1093/obo/9780199941728-0035
- LAST REVIEWED: 10 August 2020
- LAST MODIFIED: 29 November 2018
- DOI: 10.1093/obo/9780199941728-0035
The evolution of sex can be divided into two major but rather different topics, the origin and the maintenance of sex. The origin of sex is speculative because it is difficult to reconstruct. Sex originated early in the evolution of life and has general features being shared by all higher organisms, such as the generation of haploid gametes (eggs and sperm) and their fusion which is accompanied by the exchange of genetic material (see the Origin of Sex and Definitions of Sex and Asex). The maintenance of sex is a much more debated topic in evolutionary biology. Because sex is costly in evolutionary terms, but at the same time widespread among eukaryotes, it presents an evolutionary paradox. More than twenty-five different hypotheses have been put forward by theoretical evolutionary research in the 1970s and 1980s to explain why sex is evolutionary advantageous (see the History of the Paradox of Sex). The majority of these hypotheses can be divided into two major groups. (1) Sex provides novel and mostly advantageous genetic variation in offspring by reshuffling genes during recombination and meiosis. Natural selection can act on this variation and sex thus provides the opportunity for novel fast adaptations, for example to changing environments (see Changing Environments and Sexual Advantages and the Red Queen). (2) Sex removes negative, deleterious mutations through meiosis and recombination (see Modeling Epistasis, Recombination, and the Benefits of Sex, Kondrashov’s Hatchet, and Muller’s Ratchet). Certain animals and fungi might have persisted without any sex for millions of years, the so-called Ancient Asexual Scandals. The majority of asexuals are of more recent origin (see the Distribution of Asexuality in Animals and Plants), and many different forms of nonsexual reproduction have originated (see Definitions of Sex and Asex, Asexuality and Apomixis in Plants, and Asexual Reproduction in Animals). Asexual reproduction can furthermore be combined with occasional sexual reproduction. This amazing diversity in reproductive modes is translated in a plethora of hypotheses on the paradox of sex. Testing these hypotheses, or combinations of several of these, is the challenge we face. Indeed, there is still no general explanation for the maintenance of sex that is applicable to all eukaryotes, and the paradox of sex remains largely unresolved to date. The paradox of sex is not only an academically relevant question, but has also many applied aspects, for example in agriculture, medicine, and human reproductive technologies (see Applications for Society).
Several books provide a good introduction to the topic. Williams 1975 and Maynard Smith 1978 were among the first to recognize the paradox of sex. Their theoretical approach was complemented in Bell 1982, which also described the variety and taxonomic distribution of asexuality in eukaryotes, while Suomalainen, et al. 1987 provided an overview of the karyological and cytogenetic mechanisms of asexuality. Margulis and Sagan 1986 is a highly controversial book on the origin of sex. Avise 2008 and Martens 1998 provide overviews on asexuality in certain animal groups, while Schön, et al. 2009 approaches the topic from an asexual point of view.
Avise, John. 2008. Clonality: The genetics, ecology, and evolution of sexual abstinence in vertebrates. Oxford: Oxford Univ. Press.
Although this book focuses mainly on vertebrates, it provides a very accessible introduction into the topic, distinguishing between parthenogenesis and gynogenesis and clonality at different levels (within and between individuals) and environments (nature versus lab). Very suitable for all readers, especially undergraduates.
Bell, Graham. 1982. The masterpiece of nature: The evolution and genetics of sexuality. Berkeley: Univ. of California Press.
A real classic in the field and often cited because it was Bell who stated that “the paradox of sex is the queen of problems in evolutionary biology” (p. 19). Discusses all existing evolutionary theories of the 1980s, plus provides the most complete overview of the occurrence of asexuality in animal taxa. Well written and accessible for students of all levels.
Margulis, Lynn, and Dorion Sagan. 1986. Origins of sex: Three billion years of genetic recombination. Bio-Origin Series. New Haven, CT, and London: Yale Univ. Press.
This book is highly controversial because it uses cannibalism to explain the origin of sex. It is pleasant to read because it is well written and suitable for all levels.
Martens, Koen, ed. 1998. Sex and parthenogenesis: Evolutionary ecology of reproductive modes in non-marine ostracods. Leiden, The Netherlands: Backhuys.
This edited multi-author book provides a general introduction to the paradox of sex and then describes and discusses various aspects of sex and parthenogenesis in the model group, nonmarine ostracods (Ostracoda, Crustacea), including paleontological, ecological, and genetic studies. Suitable for all students.
Maynard Smith, John. 1978. The evolution of sex. Cambridge, UK: Cambridge Univ. Press.
Provides the theoretical background for thirty years of research on the paradox of sex and is a real groundbreaker. Because of the modeling and theoretical approach, it might be more suitable for advanced students. Interested undergraduate students might be better off with Maynard Smith’s Evolutionary genetics (2nd ed. Oxford: Oxford Univ. Press, 1998).
Schön, Isa, Koen Martens, and Peter van Dijk, eds. 2009. Lost sex: The evolutionary biology of parthenogenesis. Dordrecht, The Netherlands: Springer.
This multi-author edited book covers various topics of the research field, including three major hypotheses and twelve animal and two plant case studies, illustrating the amazing variety of reproductive modes. Also, related topics such as clonality, asexual species, geographic parthenogenesis, and applied aspects are provided. It is the most recent overview of the topic, suitable for readers of all levels.
Suomalainen, Esko, Anssi Saura, and Juhani Lokki. 1987. Cytology and evolution in parthenogenesis. Boca Raton, FL: CRC Press.
This book focuses on karyological variation in parthenogenesis, describing the different mechanisms and their consequences for generating genetic variability. Suitable for readers of all levels.
Williams, George C. 1975. Sex and evolution. Princeton, NJ: Princeton Univ. Press.
George Williams provides an extensive argument for why the prevalence of sex is in conflict with evolutionary theory. A real classic using different model systems, diverse forms of sexuality; also describes the effect of sex on organic and biotic evolution. Very accessible.
Users without a subscription are not able to see the full content on this page. Please subscribe or login.
- Adaptive Radiation
- Ancient DNA
- Behavioral Ecology
- Canalization and Robustness
- Cancer, Evolutionary Processes in
- Character Displacement
- Cognition, Evolution of
- Constraints, Evolutionary
- Contemporary Evolution
- Convergent Evolution
- Cooperation and Conflict: Microbes to Humans
- Cooperative Breeding in Insects and Vertebrates
- Cryptic Female Choice
- Darwin, Charles
- Disease Virulence, Evolution of
- Diversification, Diversity-Dependent
- Ecological Speciation
- Epigenetics and Behavior
- Epistasis and Evolution
- Eusocial Insects as a Model for Understanding Altruism, Co...
- Evidence of Evolution, The
- Evolution and Development: Genes and Mutations Underlying ...
- Evolution and Development of Individual Behavioral Variati...
- Evolution, Cultural
- Evolution of Animal Mating Systems
- Evolution of Antibiotic Resistance
- Evolution of New Genes
- Evolution of Plant Mating Systems
- Evolution of Specialization
- Evolutionary Biology of Aging
- Evolutionary Biomechanics
- Evolutionary Computation
- Evolutionary Developmental Biology
- Evolutionary Ecology of Communities
- Experimental Evolution
- Field Studies of Natural Selection
- Founder Effect Speciation
- Frequency-Dependent Selection
- Fungi, Evolution of
- Gene Duplication
- Gene Expression, Evolution of
- Gene Flow
- Genetics, Ecological
- Genome Evolution
- Geographic Variation
- Group Selection
- History of Evolutionary Thought, 1860–1925
- History of Evolutionary Thought before Darwin
- History of Evolutionary Thought Since 1930
- Human Behavioral Ecology
- Human Evolution
- Hybrid Speciation
- Hybrid Zones
- Identifying the Genomic Basis Underlying Phenotypic Variat...
- Inbreeding and Inbreeding Depression
- Inclusive Fitness
- Innovation, Evolutionary
- Islands as Evolutionary Laboratories
- Kin Selection
- Land Plants, Evolution of
- Landscape Genetics
- Landscapes, Adaptive
- Language, Evolution of
- Macroevolutionary Rates
- Male-Male Competition
- Mass Extinction
- Mate Choice
- Maternal Effects
- Medicine, Evolutionary
- Meiotic Drive
- Modern Synthesis, The
- Molecular Clocks
- Molecular Phylogenetics
- Mutation Rate and Spectrum
- Mutualism, Evolution of
- Natural Selection in Human Populations
- Natural Selection in the Genome, Detecting
- Neutral Theory
- New Zealand, Evolutionary Biogeography of
- Niche Construction
- Niche Evolution
- Non-Human Animals, Cultural Evolution in
- Origin and Early Evolution of Animals
- Origin of Eukaryotes
- Origin of Life, The
- Paradox of Sex
- Parental Care, Evolution of
- Personality Differences, Evolution of
- Phenotypic Plasticity
- Phylogenetic Comparative Methods and Tests of Macroevoluti...
- Phylogenetic Trees, Interpretation of
- Polyploid Speciation
- Population Genetics
- Population Structure
- Post-Copulatory Sexual Selection
- Psychology, Evolutionary
- Punctuated Equilibria
- Quantitative Genetic Variation and Heritability
- Reaction Norms, Evolution of
- Reproductive Proteins, Evolution of
- Selection, Directional
- Selection, Disruptive
- Selection Gradients
- Selection, Natural
- Selection, Sexual
- Selfish Genes
- Sexual Conflict
- Sexual Selection and Speciation
- Sexual Size Dimorphism
- Speciation Genetics and Genomics
- Speciation, Sympatric
- Species Concepts
- Species Delimitation
- Sperm Competition
- Systems Biology
- Taxonomy and Classification
- Tetrapod Evolution
- The Philosophy of Evolutionary Biology
- Trends, Evolutionary
- Wallace, Alfred Russel