Gut Bacteria and Human Evolution
Gut instinct tells me that cosmic rays are an important factor in human evolution, and that humans have evolved much more recently than scientists can ascertain (they basically only have bones to look at, whereas we are much more than just bones). But it’s not just cosmic rays, but rather a collection of factors that might occur at the same time during and after a global cataclysm:
- Punctuated equilibrium
- Cosmic Rays – they certainly cause genetic mutations in humans, and a mass influx of cosmic rays could accelerate mutations
The problem with human genetic mutations is that they are random. And if everyone has different mutations, that won’t lead to evolution. If everyone mutated in similar ways, then that would be different.
Until now I figured that our DNA repair mechanisms were the solution. I won’t go into it deeply here, but there is evidence that our DNA not only has the ability to repair damage, it can also do so in a selective manner. Effectively it can choose to leave mutations that might be beneficial, and potentially that could lead to evolution if there was enough mutating going on.
Here’s a more elegant solution that perhaps nobody else has thought of yet.
The human body carries about 100 trillion microorganisms in its intestines, a number ten times greater than the total number of human cells in the body. The metabolic activities performed by these bacteria resemble those of an organ, leading some to liken gut bacteria to a “forgotten” organ.
Though people can survive without gut flora, the microorganisms perform a host of useful functions, such as fermenting unused energy substrates, training the immune system, preventing growth of harmful, pathogenic bacteria, regulating the development of the gut, producing vitamins for the host (such as biotin and vitamin K), and producing hormones to direct the host to store fats.
Because bacteria are less complicated organisms than humans – and rapidly multiplying – they are more likely to evolve en masse during a great influx of cosmic rays.
A 2010 experiment led by Eugene Rosenberg of Tel Aviv University found that raising Drosophila pseudoobscura fruit flies on different diets altered their mate selection: the flies would mate only with other flies on the same diet. A dose of antibiotics abolished these preferences—the flies went back to mating without regard to diet—suggesting that it was changes in gut microbes brought about by diet, and not diet alone, that drove the change.
To determine whether gut microbes could affect an organism’s longevity and its ability to reproduce, Vanderbilt University geneticist Seth Bordenstein and his colleagues dosed the termites Zootermopsis angusticollis and Reticulitermes flavipes with the antibiotic rifampicin. The study, published in July 2011 in Applied and Environmental Microbiology, found that antibiotic-treated termites showed a reduced diversity in their gut bacteria after treatment and also produced significantly fewer eggs. Bordenstein argues that the reduction of certain beneficial microbes, some of which aid in digestion and in the absorption of nutrients, left the termites malnourished and less able to produce eggs.
These studies are part of a growing consensus among evolutionary biologists that one can no longer separate an organism’s genes from those of its symbiotic bacteria. They are all part of a single “hologenome.”
So in terms of survival of the fittest evolution, gut bacteria being an important part of our hologenome, our own personal Gaia, they are an instrument of evolution.
But what if this instrument of evolution was itself subject to evolution?? Could the way bacteria regulates humans alter when the bacteria itself evolves? And perhaps a cosmic ray influx could trigger it?