#  Desai Lab Explains a Long-Standing Evolutionary Puzzle: Why Sex? 

 





May 04, 2026

 

 

     ![Michael Desai working in the lab wearing a white lab coat. Credit: Niles Singer](/sites/g/files/omnuum6811/files/styles/hwp_16_9__480x270/public/2026-08/Michael%20Desai_Niles%20Singer-Harvard%20.jpg?itok=zj3x1zsD) 

Michael M. Desai  
Credit: Niles Singer/Harvard Staff Photographer



 



 

Given the substantial biological costs of sexual reproduction, why did it evolve? New research from the lab of Michael M. Desai offers a compelling answer — particularly in environments that change over time.

The study, led by Ph.D. candidate Shreyas Pai and former postdoc Parris Humphrey, used yeast as a model system because the organism can reproduce either sexually or asexually and completes a new generation every 90 minutes, allowing the team to track evolutionary change across hundreds of generations in just months.

Published in [*Science*](https://www.science.org/doi/10.1126/science.aec9708), the research began with identical yeast populations evolving under favorable conditions, with select lines periodically induced to reproduce sexually. The team confirmed that sexually reproducing populations gained more fitness than asexual ones in stable environments, and found similarly consistent advantages when populations were challenged with saltier, hotter, more acidic, or phosphate-limited conditions.

The researchers also uncovered a mechanism behind that advantage: genes with multiple effects can carry neutral or mildly harmful "hitchhiking" traits alongside beneficial ones. When environments shift, those hidden liabilities can become costly. Because sexual reproduction reshuffles parental genomes, it allows populations to purge such harmful hitchhikers — an option unavailable to asexual populations, whose offspring are genetic clones.

"We believe that this general mechanism by which sex speeds adaptation and purges hitchhiking deleterious load should be a general advantage of sex across all sorts of organisms," said co-author Desai.



 

 

 



 

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