Hard Workers of Evolution

Over a year and half ago, I laid out the four general expectations that arise from the hypothesis of front-loading evolution.  One such expectation was that “front-loading would be linked to terraforming.”  As I explained,

So if we are to front-load the existence of mice-like creatures into the genomes of single-celled organisms, we also need to ensure the Earth will be prepared, at some point, to receive the mice. And it is the preparation of a receptive Earth that we can call terraforming

Bacteria are easily viewed as the terraformers, where one of their most glorious successes was to draw from the ancient Earth’s abundant supplies of water and use this to oxygenate the atmosphere which in turn would facilitate the evolutionary emergence of eukaryotes, then metazoan.  Yet there is much more to bacteria.

When it became clear that the genome of a single-celled eukaryotic organism did not need to be radically retooled to transition to the multicellular state of an organism like Volvox, one of Jerry Coyne’s colleagues commented, “Maybe all the hard work was done by bacteria.”

Indeed.  Not only have bacteria terraformed our planet, but they probably facilitated metazoan evolution itself.  In fact, they may have assisted metazoan evolution such that nothing like a metazoan would have emerged had bacteria not existed.

As a tease for this shift in thinking, consider some recent research:

biologist John Jaenike and colleagues document a clear example of a new mechanism for evolution….Jaenike’s team has chronicled a striking example of a bacteria infecting an animal, giving the animal a reproductive advantage, and being passed from mother to children. This symbiotic relationship between host animal and bacteria gives the host animal a readymade defense against a hazard in its environment and thus has spread through the population by natural selection, the way a favorable gene would….. Jaenike provides the first substantial report of this effect in the wild in his paper “Adaptation via Symbiosis: Recent Spread of a Drosophila Defensive Symbiont,” but he says it may be a common phenomenon that has been happening undetected in many different organisms for ages.


My goodness.  As Jerry Coyne summarizes this research:  “Here, then, we see how a species (the fly) has adapted to an environmental challenge not by changing its genes, but by acquiring a whole genome—the Spiroplasma genome.  It’s as if the whole bacterium was an adaptive mutation.”

If bacteria can help flies to adapt to their environment (where the “environmental” pressure is biotic in nature), perhaps such symbiosis also played an important role in the emergence of metazoans themselves (as I have predicted).

In the next entry, let’s look at another more radical example where symbiogenesis may have been in play that will enhance the plausibility of this prediction.


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