Feb 29, 2016 | By

A Curious Relationship between Sex and Mathematics

As noted in the Economist (2-27-16, p71), Michael Desai and his colleagues at Harvard (article published in Nature) report that “Sex Speeds Adaptation by Altering the Dynamics of Molecular Evolution.” The findings arise from Desai’s research with yeast, which reproduces both sexually and asexually. This feature has allowed Desai et al to experiment with the evolution of mutations in yeast populations that are limited to either one or the other reproductive modes.


Desai Lab, Harvard

Previously, the only experimentally validated explanation for why sex evolved was the “Red Queen” strategy – faster genetic mixing from sexual reproduction makes it harder for pathogens to catch up. (The Red Queen in Alice in Wonderland has to keep running just to stay in the same place.)   With Desai’s research, “Plucking rubies from the rubbish” has now also been shown to be valid, and it is perhaps more fundamental. Mutations under asexual reproduction are always linked together in a given genetic line, making it impossible for the selection pressures in the environment to promote a single mutation without also allowing all the others, some of which may be disadvantageous. But in sexual reproduction, the genetic mutations are divided out and mixed in subsequent generations – selection pressures can thus come to bear directly on specific advantageous (or disadvantageous) mutations. Sexual reproduction speeds up adaptation, making evolution itself more efficient.

The math in this case is pretty simple, unlike the complex examples discussed in the article on Order in Randomness.  Dividing the genes up in pairs across succeeding generations, rather than keeping them in separate lots, increases mixing and diversity, which gives evolution a lot more material to work with. Since this is the case, it is likely that any advanced system of biological evolution, in theory or on other planets, would eventually find a similar solution – sexual reproduction. So the simple math is driving a key and profound feature of our own evolutionary heritage, one that appears likely to be universal – sex.

This finding reinforces a sense that evolution is not random. In this case, the mathematics of mixing directs evolution down a pathway to sexual reproduction and all that it implies – mating rituals, sex hormones, pheromones and all the rest (maybe even poetry!).   Sex has a special and privileged role in the universe.

This leads one to ponder – is the world and life created, or just happenstance? Are we just lucky to be alive, conscious, self-reflective and empathic sexual beings? Or is there a pattern in all this weirdness – a pattern that carries with it an intention and purpose imbued in the universe since the beginning of time?

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