Retroviruses from the Cosmos

Viruses are remarkably efficient biological entities, incredibly small in size—ranging from tens to hundreds of nanometers—often smaller than the wavelength of visible light. They consist of nucleic acids (either DNA or RNA) encased in a protein shell known as a capsid. Essentially, viruses act as parasites, invading living cells and reprogramming them to facilitate their own replication, often at the expense of the host's health, as evidenced by the ongoing COVID-19 pandemic.

Viruses exist at the intersection of life and inorganic matter, containing a dense amount of information in a compact form and possessing significant control over living organisms. Retroviruses, in particular, exemplify this concept.

Upon invading a host cell, a retrovirus utilizes the enzyme DNA polymerase to convert its RNA genome into DNA. This process reverses the typical cellular function, where DNA usually serves as the template for RNA synthesis. The term 'retrovirus' arises from this reverse mechanism. Once the DNA is created within the host, the integrase enzyme integrates this viral genetic material into the host's DNA. In future cell replications, the virus, now termed a provirus, is replicated alongside the host's genetic material. If the infected cell is a gamete (reproductive cell), the virus can spread through subsequent generations, aligning its interests with those of the infected organisms.

Due to their diminutive size, information density, and control over living systems, retroviruses are viewed by panspermia proponents as ideal mechanisms for explaining how extraterrestrial organisms could influence Earth's biological evolution.

The panspermia hypothesis posits that life did not simply arrive on Earth once via comets; rather, it suggests a continual influx of biological materials from space has shaped the evolution of life throughout Earth's history.

In a study featured in Progress in Biophysics and Molecular Biology, Steele and colleagues address a significant critique of this hypothesis:

> (… ) How can a virus from space anticipate the range of organisms it will encounter upon arrival? (… ) The evolution of viruses in a cosmic context is deeply intertwined with life on Earth. Their host specificity is typically limited to closely related species defined by their evolutionary lineage.

For instance, the influenza A virus can be cultured in hen's eggs, reflecting its host specificity over a 50 million-year evolutionary history, while the Ebola virus specifically targets primates.

In Appendix A of the same study, the authors clarify their stance on the shared cosmic origins of all life forms:

> The internal evidence from terrestrial biology suggests that all habitable planets within the galaxy form a single interconnected biosphere. Life forms elsewhere are expected to exhibit convergent patterns of genotypes and phenotypes, shaped by natural selection (both Darwinian and Lamarckian) in their respective planetary environments.

Yet, questions arise regarding how viruses carried by comets could endure for millions of years against harsh conditions such as extreme cold, radiation, and cosmic rays. The authors respond, perhaps with excessive optimism:

> Bacteria and viruses embedded in rock grains, carbonaceous matter, or ice are shielded from radiation damage and can remain viable for millions of years in space. Microorganisms, including viruses, preserved within cometary bodies could survive indefinitely, as recent space experiments aboard the International Space Station have shown.

Concerns about the intense heat generated during a comet's atmospheric entry also persist. How do viruses endure the thermal shock and revive post-impact?

Steele and colleagues assert that the small size and vast numbers of viruses suffice. Their diminutive nature makes them less susceptible to damage from radiation and high-speed impacts during atmospheric entry. Even if many specimens are lost during their journey or upon Earth's arrival, their sheer abundance in the cosmos means that considerable losses would not be catastrophic:

> Their ability to replicate allows them to exist in vast quantities on cosmic scales; thus, even significant losses due to inactivation leave millions of potentially infectious particles behind.

Ultimately, proponents of panspermia contend that the evolution of life on Earth, including human evolution, has been influenced not only by natural selection and genetic mutations as per neo-Darwinism but also significantly by extraterrestrial factors. These factors align with Lamarckian principles, which posit that traits acquired during an individual's lifetime can be passed on to offspring.

In this framework, spaceborne viruses would act as catalysts for significant epidemics, such as the Spanish flu or HIV, and could also guide the evolutionary trajectories of life forms in response to viral infections.

Extraterrestrial Octopuses

According to the same study, octopuses may represent an unexpected evolutionary outcome influenced by viruses from space. Tracing the evolutionary lineage of the subclass Coleoidea, to which octopuses belong, back to their nautiloid ancestors from the late Cambrian period, one might conclude that octopuses seem like beings from a future era due to their remarkable and rapid diversification compared to preceding species:

> Their large brains, advanced nervous systems, camera-like eyes, flexible bodies, and ability to camouflage instantaneously by altering color and shape are just a few of the notable traits that suddenly appeared in the evolutionary timeline. The transformative genes connecting the ancestral Nautilus to the common Cuttlefish, Squid, and common Octopus are elusive in any prior life forms, suggesting they may have been derived from a distant "future" in terrestrial evolution, or more realistically, from the cosmos.

Octopuses are indeed extraordinary creatures, known for their intelligence, unique physical capabilities, and an incredibly complex genome comprising over 33,000 protein-coding genes. But what scientific evidence supports the notion that they embody a break from traditional Darwinian evolution?

While there may not be definitive proof, there is at least an intriguing clue. In many organisms, including humans, DNA transcription via messenger RNA (mRNA) can be modified by enzymes that convert adenosine to inosine. This editing mechanism occurs frequently in squids and especially in octopuses, distinguishing them from other species, including humans, whose transcriptomes have been studied. Notably, this mRNA editing process is absent in nautiloids, the cephalopods that descended from the common ancestor of squids and octopuses.

For Steele and colleagues, this significant difference in gene expression indicates that octopuses and squids represent a sudden evolutionary leap that cannot be explained through conventional neo-Darwinian gene modification processes. So, where does their diversity come from, according to panspermia advocates? From cosmic biological contributions, of course. The authors propose that the evolution from squid to octopus aligns with the introduction of extraterrestrial genes. An even more compelling theory suggests that entire groups of extraterrestrial genes could have arrived on Earth, perfectly assembled, during a distant epoch. This scenario posits that octopus embryos were delivered to our planet around 275 million years ago, cryopreserved within comets or their debris, and subsequently survived a gentle landing into their natural marine environment.

The notion that octopus embryos could have reached Earth intact aboard a comet, preserved under ice for countless millennia, resembles science fiction. Yet, such ideas are central to the panspermia hypothesis.

Proponents of this theory view outer space as a vast habitat where tiny, resilient organisms like viruses and bacteria can not only endure but thrive, multiplying even amid the extreme temperatures and radiation found in interstellar dust clouds scattered throughout the cosmos.

Read the other parts of this story

• 1/6— The origin of life on Earth remains a mystery, with two main theories: Abiogenesis, favored by most scientists, and panspermia, championed by a small yet passionate group of scholars.
• 2/6— Comets as vectors of life
• 4/6— Interstellar bacteria and mass extinctions
• 5/6— The biological Big Bang
• 6/6— An eternal and uncreated Universe