Chapter 7 Sex

Chapter Seven

Is sex good for survival?

Why study the evolution of sex?

Sex results in offspring with DNA from more than one parent. Sexual reproduction is so common and familiar that it may come as a surprise to find that it has been an enduring puzzle in evolutionary biology. Given that many species can reproduce uniparentally, without needing to combine genes with other individuals, why would sex evolve? And given that asexual lineages frequently evolve from sexual species, why do so many different species retain sexual reproduction? There have been many different solutions proposed for both the origin and maintenance of sexual reproduction, ranging from genome repair to long-term evolvability. This broad range of proposed mechanisms requires us to think about how evolution works at different levels of biological organisation, from “selfish genes” to evolutionary lineages, and at different timescales, from individual lifetimes to millions of year.

What are the main points?

  • When reproducing entities (such as individuals) are made up of multiple units that also have the capacity for copying themselves (such as genes), we have to think about the way selection acts at different levels of biological organisation.
  • Fitness benefits at one level of biological organisation may come at the cost of the capacity of other levels to leave descendants, and different players in a system may benefit from different reproductive strategies
  • We might seek separate explanations for the origin and maintenance of complex traits: uncovering the selective pressures that generated the capacity for genetic exchange may tell us little about why most living eukaryotic species retain sexual reproduction.

What techniques are covered?

  • Evolutionarily stable strategies: the fittest variant needs to be considered in terms of the other possible variants in the population.
  • Genetic conflict: genes within a genome may have different ideal strategies for reproduction, and this may be reflected in evolution of genomic architecture, individual behaviour, and long term lineage evolvability.

What case studies will be included?

Phylogenetic models of macroevolution: ‘tippy’ distribution of asexuality on the tree of life


Image: Rod Peakall, all rights reserved.