Pathogens Devolved
They’re calling it evolution, but it’s easier to be
a freeloader than an independent organism.
Why work, if you can get away with stealing? Some young adults, gifted with healthy bodies and bright minds, are freeloaders. The paradigmatic freeloader wastes his life in his parents’ basement playing video games and interacting with friends on social media. He feeds off the parents’ refrigerator instead of getting a job and making his own money. Once in awhile dad lectures him about how he had to wash dishes and clean toilets to earn enough to eat when he was the son’s age. But life is good, the shiftless son thinks, as long as he doesn’t make his parents sufficiently upset with him to kick him out of the house. The freeloader doesn’t realize that the more he loafs, the weaker and more dependent he becomes.
Is this how some originally independent organisms became parasites and pathogens? We can’t accuse microbes of moral lapses, of course, but it’s easier for any organism to live off another’s resources than to do its own hard work. Scientists at Waginengen University think they have found a case of this “evolutionary” scenario.
Scientists shed light on the emergence of pathogenic bacteria (Waginengen University via Phys.org, 8 July 2022).
While most micro-organisms are benign or even essential to sustain life, some bacteria are known to cause disease in organisms like humans, animals and plants. Intracellular pathogens can establish persistent and sometimes lifelong infections. While bacterial pathogens are known to have evolved multiple times independently, not much is known about their evolutionary origin. The new research published in Nature Microbiology reveals how Rickettsiales, a group of obligate intracellular bacteria that includes several notorious pathogens of humans and cattle, evolved from once free-living bacteria.
If this is evolution, it is devolution—a change for the worse, from strong and free-living to degenerate and parasitic. Like the freeloading son, the free-living ancestor had all the resources to live independently but took up residence in another cell’s house.
Researchers noticed this possibility when they looked at genomes of marine bacteria. They found similarities to parasites in the Rickettsia family. It suggested to them that the pathogens had shed genes they used to have. At some point they found it more convenient to live as parasites. And along with the parasitic lifestyle came diseases to the animal or human hosts that would have tolerated otherwise beneficial microbes.
Genes typically involved in pathogenic lifestyles, such as those involved in energy parasitism or host cell manipulation, were not identified. The researchers did however find genes encoding a so-called “type 4 secretion system,” a microscopic needle-like structure used by bacteria to interact with host cells. “We speculate that this system is not necessarily used to interact with host cells like other Rickettsiales, but rather to kill competing bacteria, or to fence off predatory microbes,” Martijn adds.
A stepwise process led the pathogen to “repurpose” machinery it already had, they say, and use it for its own ends instead of the good of the host. The Type 4 Secretion System is a complex injection machine (see my report at Evolution News, 14 May 2014) that allows bacteria to share genetic material and proteins via conjugation. In the possession of a parasite, it becomes a weapon.
By comparing the genomes of the newly discovered species with those of previously known Rickettsiales, the team of researchers managed to reconstruct the evolution of host association and pathogenicity in the Rickettsiales. “We suggest that the free-living ancestor of Rickettsiales repurposed its needle-like type 4 secretion system to interact with and manipulate host cells,” Ettema speculates.
The authors are careful to note they are speculating on this type of “evolution” which is actually degeneration. Analogies could be drawn with other parasitic situations like “brood parasitism” where some birds let other species sit on the nest so they don’t have to. Such patterns can persist if the host lets the parasite get away with it.
The original creation was free of pain. Photos by DFC from the AiG Creation Museum.
This case cannot answer all the complex situations of parasitism, but is worth noting. The researchers found free-living counterparts in ocean plankton that live ‘responsibly’ so to speak. Those independent microbes contain the Type 4 Secretion System (T4SS) and use it for interactions with other microbes, including sharing information. One might compare it to workers in a business sharing their skills for the good of the company, or members of a town cooperating for the common good. The parasite is like the freeloading son using his resources for selfish purposes. In both cases, it is easier for the parasite to devolve rather than to invent machinery like a T4SS from scratch.
The world today is filled with parasites, pathogens and suffering. In Genesis 3, after sin entered the paradise he had made, God warned the first man and woman who had rebelled against his leadership that the world would be a hard place under their chosen master, the serpent. There would be sweat, thorns, and pain, ending in death for them and their offspring. In this picture of pathogens, God would not have had to ‘invent’ painful things from scratch when he pronounced the curse as judgment on Adam and Eve. He could have simply released the
The curse made it hard to live in the world, but God did not leave himself without witness (Acts 14:14-18).
controls that were keeping microbes in their place. The curse was tough love, like caring parents allowing a shiftless son to suffer the consequences of his irresponsibility (cf. Romans 1:18-32) to learn a lesson. Such tough love led the Prodigal Son to appreciate what he had lost.
After the curse, perhaps God gave Satan some limited control of the ecology within his permissive will, allowing Satan and his minions to tweak existing organisms and make them more harmful. We know the ‘god of this world’ hates mankind and loves death. Behind the scenes, though, God was working out his eternal master plan to redeem mankind and the world (Genesis 3:15). In the future redeemed Creation, there will be no more curse and no more pain.
If the scientists can speculate about the origin of pathogens, we can, too. Our speculations have the advantage of fitting within the record of eyewitnesses about what happened at the beginning.