“The little things are infinitely the most important.” ~ Irish-Scots novelist and physician Arthur Conan Doyle
For nearly 3 billion years, life on Earth kept to tiny single cells. These productive inhabitants were prokaryotes, of 2 main varieties: bacteria and archaea.
In their initial eon, archaea dabbled in most every lifestyle, from eating photons to consuming chemical compounds. The phototropism of archaea was much simpler and direct than photosynthesis, which is a complex quantum process. Various archaea were autotrophic, heterotrophic, or saprotrophic.
Meanwhile, bacteria made a living chewing rocks: unlocking energy from sulfur, nitrogen, iron, and hydrogen. This created sediment that acted as a geologically viscous lubricant, which was instrumental in generating tectonic plate subduction. By this, bacteria facilitated the rise of continents.
Cyanobacteria arose by deriving energy from fermentation, which does not require oxygen. By 3.5 bya, cyanobacteria had acquired the quantum trick of photosynthesis: microscopic reactors, capturing fleeting photons to convert carbon dioxide and water into the universal organic currency for energy: the sugary molecule ATP.
“During the first half of Earth’s history, the majority of life forms were probably capable of photosynthesis.” ~ Columbian biologist Tanai Cardona
Thus chlorophyll was born. It literally changed the world. Animal life on Earth was made possible by the byproduct of photosynthetic bacteria: oxygen.
At first, oxygen was poisonous to life. But organisms adapted and evolved to appreciate the accessible energy that atmospheric oxygen offered.
Oxygenating the atmosphere altered every form of life. Even prodigal oxygen producers had to adapt to their own success.
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Through exquisite adaptation, microbes perfected metabolism to near the optimality afforded by physical chemistry, with the slight trade-off of being able to adjust to alternative nutritional conditions. This efficiency goes a long way in explaining the diversity and staying power of microbes.
Viruses descended from bacteria ~4 billion years ago, slimming down to live vampirishly. But they kept their wits about them. Viral exuberance for communion with others is positively infectious.
“No phone, no pool, no pets… king of the road.” ~ American musician Roger Miller in the song “King of the Road” (1964)
Viruses travel light. While hardy enough to survive the elements, they enjoy the comfort of being indoors.
Physically, a virus is little more than a genetic package inside a protein coat. It cannot eat or reproduce. What a virus can do is hijack a host cell and run it to make copies of itself: the naked virus substituting itself for the host cell chromosome. To spread, the viral offspring must find a new host.
Viruses are everywhere; inflicting themselves on all other life. Every organism is constantly interacting with viruses.
In selecting only those sequences that may prove beneficial, the rapid evolution of viruses shows that they are intelligent genetic mavens.
Given their line of work, viruses are extensive travelers, to put it mildly. In constantly encountering one another, viruses constitute a worldwide community.
The descent of viruses has been obscured by their willful genetic maneuvers, which caused dramatic transformations. The significance of viruses on other life has been indelible.
Universal Common Ancestor
“Viruses are embedded in the fabric of life.” ~ Argentinian biologist Gustavo Caetano-Anollés
In the 1740s, French natural philosopher Pierre Louis Maupertuis suggested that all of life had a common ancestor. The idea became something of a holy grail for evolutionary biologists: to find the organism from which all others descended. It turns out the culprit was a carrier, not a progenitor.
Archaea and bacteria are the earliest-known life forms. They seem to have originated independently, but both ended up with the same genetic coding regime.
In a world when rough-and-ready RNA made life less robust than it could be, viruses spread an innovation that gained universal acceptance by virtue of its durability: DNA. A critical tweak in a sugar molecule improved fidelity and gave much better ability to withstand harsh environments.
Only viruses had the means, motive, and opportunity to unify life at the genetic level. While some viruses decided to continue to use RNA for their own convenience, evangelizing proponents of DNA inspired prokaryotes worldwide to adopt a superior solution to managing their library of life, known as a genome.
As a regular work practice, viruses insert genes into their hosts. By this and their unwanted intrusions, viruses drive evolution. 8% of human DNA derived from viruses. In many instances, these viral contributions are critical.
Viruses are gregarious: establishing networks of connections between compatriots. Cooperation among viruses during infection is common, as the process is seldom easy.
The advantage of viral cooperation comes in taking advantage of specialized skill sets. Some viruses are better at certain tasks than others.
Decisions need to be made. For example, to boost total viral production, host cells may be granted greater longevity.
If a virus is co-infecting with a stranger instead of friends, it considers this competition. The virus will work its host cell to death as quickly as possible, to thwart its rival.
Viruses understand the difference between strategy and tactics. With their sharp minds, viruses amply illustrate that physicality has nothing to do with wiles.
Influenza viruses are shrewd. Many originate in birds; hence the commonly bandied term avian flu. This host platform is especially convenient, as birds are gregarious and often travel widely.
From their avian base, flu viruses can jump to various mammals: rodents, cats, dogs, pigs, ferrets, camels, cetaceans, and primates. These viruses are well-adapted to survive on surfaces that provide easy access. At every step, flu viruses are ready with an array of potential modifications that they may apply to gain entry to a new host species.
Viruses also have numerous countermeasures they may employ against immune systems, which vary somewhat between species. This is why flu viruses are so successful, and influenza never defeated.
Measles is especially thoughtful in its thoroughness. ~2 days after the virus enters the body it finds its way to the lymph nodes. This provides for widespread distribution. A couple of days later, blood vessels are carrying virus-laden cells throughout the body.
Symptoms only appear 7–10 days after infection. Such discretion affords airborne infectious contamination of other unsuspecting hosts. Viruses love neighborhood parties.
The body belatedly responds with coughing, sneezing, and fever as viral loads peak. In reply, measles advertises its victory with red bumps across the skin.
“The measles virus preferentially infects cells in the immune system that carry the memory of previously experienced infections.” ~ Dutch virologist Rik de Swart
To conclude its triumph, measles smartly wipes the immune system’s memory of its visit. This permits successful reinfection at a future date. Hence the especial importance of vaccination against measles.
The cucumber mosaic virus infects garden-variety vegetable plants. Upon doing so, the virus makes the smell of those plants more alluring to aphids, which the virus employs as transport.
The infected plants do not live up to their odor. A single taste disgusts the aphid, which moves on.
That is a good thing for the virus, which hitched its ride when the aphid landed and sampled. If the aphid had stayed to dine, working its needle-like mouthparts deep into the plant, the virus would likely have been wiped off. Thus, the mosaic virus cleverly manages both the come-on and the brush-off to suit its needs.
The virus goes one further. It programs the plant, which may look weak and wretched from its infection, to nevertheless make itself smell alluring to pollinators.
“In making them more attractive to pollinators the virus gives these plants an advantage.” ~ English plant pathologist John Carr
The virus doesn’t hitch a ride on the bees that come calling for pollen, relying instead on its trusty aphids to porter it to the next plant; but the bees that spread the pollen around engender the next generation of plant to be more susceptible to infection. This virus plans ahead.