Is there any immortal creature in the world? Despite only being only three millimeters in diameter on average, adult versions of immortal jellyfish (Turritopsis dohrnii) have a huge party trick: they can roll back their biological clock when injured or on the verge of starvation. This means, in theory, they could live forever. Could humans harness their abilities to eradicate ageing completely?

       As scientists have known, the reason of human ageing is a process called trans-differentiation. “This is about how a fully formed specialized adult cell can become another type of specialized adult cell. It’s how a cell can adapt,” explains Dr. Maria Pia Miglietta. The exact mechanism behind trans-differentiation is still a mystery to scientists. However, as Miglietta explains, the answer will likely be found in the jellyfish’s genes. “It most certainly has something to do with the DNA,” she says. “It’s the DNA that programs a cell––certain genes being ‘turned on’ or ‘off’ will determine what sort of cell it is. We’re far away from any kind of real-world application,” says Miglietta. “But we hope that studying what happens in these jellyfish can tell us how their genes change cells––and how these changed cells integrate with others. This is the base of understanding cellular regeneration and tissue regeneration.” 

      However, there are many challenges. These jellyfish have only been studied sporadically since the early 1980s, meaning experts have only a few decades’ worth of data. While an immortal jellyfish can age in reverse, it can also be easily killed by predators including various fish, sharks, turtles and even other jellyfish. “They’re incredibly sensitive, from the water temperature to their plankton and fish egg diet,” says Miglietta. “The real paradox is they’re actually really hard to keep alive!”

   In the United States, there are about twenty-two million hearing-impaired people; of these, two million are profoundly deaf (unable to hear any thing) or severely deaf (unable to hear much). Hearing impairment results from three major factors that are not necessarily exclusive: environmental, hereditary and old age.

   Environmental causes include noise-induced, accidental, toxic, and viral. Noise-induced deafness is primarily a phenomenon of the modern industrial world, though stonemasons, may have been subject to hearing-loss in the ancient world. Permanent deafness resulting from toxicity is also a phenomenon of the modern world. Deafness from accident, such as a blow to the ear, must have resulted from time to time. Viruses, too, were very much part of the ancient world. Of the six main viruses that can cause deafness today—chickenpox, common cold viruses, influenza, measles, mumps, and poliomyelitis—there is evidence for five in ancient Greece. There is also evidence for the presence of bacterial meningitis, whose classic complication is hearing loss. In modern, developed countries, preventative medicine reduces the incidence and severity of these viruses, but in the ancient world, as in third-world countries today, these viruses must have taken their toll.

   There is no reason to rule out hereditary deafness in the ancient world, and there is some conjectural evidence for the results of in-breeding, although not specifically for deafness. In addition to inbreeding, other hereditary factors would have produced deafness. Some families simply have a genetic background that favors deafness.