On this week’s airing of “Wait Wait … Don’t Tell Me!” the weekly NPR news quiz, comedienne Paula Poundstone declared something that should make any science-literate person cringe, “without sex there can be no evolution.”
This statement dismisses the fact that the vast majority of life on this planet is not sexual yet they evolved and continue to do so!
The plants and vertebrate animals of the macroscopic world have largely been described, 85 – 90% of them. However, it is believed that we only know about less than 1% of the bacterial and archaeal species and less than 5% of fungal species that exist on this planet. Microorganisms are extremely diverse, at the DNA level, in the biochemical feats of metabolism they collectively perform to survive, and in the varied ecological niches they inhabit. We have only just begun to fully appreciate their ubiquity, diversity, and magnificence.
But back to sex and evolution.
Whereas most ‘higher’ organisms reproduce sexually, many organisms, mostly microbes, reproduce ‘asexually’ without a partner, or at least have this option, and these organisms still evolve.
For example, the bacterium Escherichia coli can reproduce with or without sex. Sex, although it can contribute, is not a prerequisite of microbial evolution. Genetic change is.
An individual cell of E. coli grows until it is approximately twice its original size and has duplicated its single chromosome, then divides by binary fission into two ‘daughter’ cells. It has reproduced, without sex. Each resulting cell can go on to divide, and so can their progeny, and so on, as long as their is enough food to feed the masses.
The two daughter cells are often identical. However, if during the process of DNA duplication the DNA is altered, any daughter that inherits an alteration is genetically changed. This change is the basis of evolution, and it can happen in the absence of sex.
Asexual reproduction is not limited to the microbial world. Most plants can reproduce asexually or sexually (via seeds or spores). One extreme example in the macroscopic world is that of Kalanchoe daigremontiana, sometimes called mother of thousands or pregnant plant. New plantlets arise along the leaf margins, as shown in the photo.
The sex life of E. coli is described in a separate article.
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You might also be interested in my other work as Long Beach Urban Agriculture Examiner and founder and director of Long Beach Grows.