How sex sheds evolutionary baggage
Why is there sex—or, more precisely, sexual reproduction? If you're an evolutionary biologist, the answer isn't obvious. Sexual reproduction is biologically costly, requiring not only competition for mates but also the creation of entire populations in which only half the individuals can give birth. That reality has led scientists to wonder why it arose in the first place. After all, in asexual…
Sexual reproduction is a costly process that requires competition for mates and the creation of new populations. This has led scientists to question why it evolved in the first place, especially when asexual reproduction allows for rapid reproduction without the associated costs. However, new research from Harvard biologists sheds light on the benefits of sexual reproduction, particularly in changing environments.
The researchers used yeast as a model organism, which can reproduce both asexually and sexually, and observed changes over 960 generations in just four months. They found that sexually reproducing populations had fitness advantages of between 2% and 5.6% over asexual populations in different environments, including altered saltiness, temperature, acidity, and phosphate levels.
One key advantage of sexual reproduction is its ability to purge harmful genetic mutations, known as "hitchhiking load," which can accumulate over time in asexual populations. Without sex, asexual populations are unable to eliminate these harmful mutations, as their offspring are genetically identical clones. In contrast, sexually reproducing populations produce offspring with a mix of their parents' genes, reducing the impact of these potentially harmful traits.
This ability to purge deleterious genetic load allows sexually reproducing populations to adapt more effectively to changing environments. The researchers believe that this mechanism of purging hitchhiking load through sexual reproduction should be a general advantage across all organisms, from simple microbes to more complex plants and animals.
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