What Doesn’t Kill You, Makes You Stronger

The COVID-19 pandemic illustrated a remarkable fact: some people do not get sick even after sharing a room or a bed with an infected person.

The same phenomenon is observed for other organisms that cause disease, namely pathogens, not only in viral but also in bacterial infections. For example, African and Asian monkeys exhibit greater tolerance compared to humans and baboons when exposed to some pathogens, and mice carry pneumonia-causing bacteria in their nasal passages without showing symptoms of illness.

A team of Harvard scientists, led by Dr. Megan Sperry, a postdoctoral fellow at the Wyss Institute, published a new paper which includes an important insight: “Current therapeutic strategies against bacterial infection focus on direct killing of bacteria with antibiotics or induction of immunological resistance through use of vaccines, each of which works by reducing pathogen load. These strategies have proven highly effective in the past, but they also have substantial disadvantages and face major challenges as development of bacterial resistance to antibiotics is becoming rampant and people must be willing to be vaccinated prior to infection to confer any defense against disease. An alternative approach is to develop therapeutics that act by augmenting host tolerance to infection in the continued presence of pathogens, rather than killing or inactivating the microbes.”

The scientists identified drugs that can keep tadpoles alive in the presence of lethal bacteria and have discovered genetic mechanisms to enhance disease tolerance, namely the ability of cells and tissues to resist damage in the presence of invading pathogens.

Here lies a broader life lesson about tolerance building. In the age of social media and a highly polarized society, any major activity — irrespective of how justified it is — receives attacks. Improving our tolerance to an attack rather than attempting to attack back could be an effective strategy for preventing destruction and avoiding an arms race in which the attacker evolves to develop the equivalent to “antibiotic resistance”. The advantage of an internal shield is that it does not force the attacker to evolve for its own survival. It simply neutralizes its effectiveness.

When life offers a choice between chess playing and mud wrestling, the favorite strategy is clearly the former. Whereas chess offers an elegant winning scheme, mud wrestling forces you to get dirty. Wars inflict wounds on both sides, as evident from the Russia-Ukraine conflict. The art of politics is to bring prosperity by minimizing damage and waste of resources. It is therefore advantageous to avoid brutal conflicts when possible.

Of course, developing resilience is insufficient for some attacks which pose an existential threat. These require a targeted defensive response. Eventually, our body weakens and something kills us. But we can extend our longevity by minimizing disruptive encounters and enhancing our tolerance to external threats.

As the philosopher Friedrich Nietzsche wrote in 1888 in his book of aphorisms, Twilight of the Idols: “Out of life’s school of war — what doesn’t kill me, makes me stronger.”

In the long-run, Darwin’s principle of “survival of the fittest” applies. The fittest may not be the strongest but the smartest.

These lessons can be extended to life in the cosmos. Nature’s lesson of “treat your body, do not kill the threat” might extend beyond pathogen tolerance in monkeys or mice to interstellar travel.

In interstellar space, the equivalents of “pathogens” are energetic cosmic-rays, X-ray and UV irradiation and bombardment by dust and gas. Consider the tiny animals Tardigrades — also known as water bears, found in wet lichens and mosses. Because their habitat often dries up, tardigrades are resilient to drying out and can resurrect after years of dehydration. In 2007 tardigrades were put aboard the FOTON-M3 spacecraft launched by the European Space Agency (ESA) and were exposed to extreme space conditions — vacuum, dehydration, X-ray and UV radiation from the Sun and cosmic rays — in a low Earth orbit with an altitude of about 270 kilometers. After their safe return to Earth, two thirds of them survived the trip, including exposure to deadly levels of solar UV radiation a thousand times higher than on the surface of the Earth. Moreover, the survivors could reproduce viable embryos after their space trip. In May 2011, Italian scientists sent tardigrades on board the International Space Station along with extremophiles on STS-134, the final flight of Space Shuttle Endeavour, and concluded that “tardigrades represent a useful animal for space research.” More recent studies indicate that tardigrades have special DNA-repair mechanisms, including a unique protein named Dsup (damage suppressor) that protects DNA from damage produced by radiation and radicals.

Tolerance to space risks may extend to technological artifacts as well. Artificial Intelligence (AI) astronauts might be roaming through interstellar space with material constructions that tolerate related existential risks. Rather than waste resources on destroying the threats along their path, they might focus on mitigation of damage and self-repair strategies, the approach taken by tardigrades.

The Galileo Project plans to study interstellar objects in search for technological relics of advanced civilizations. If this research effort will identify technological artifacts from interstellar space, it would be interesting to explore the protection mechanisms of functional devices compared to defunct space trash. This would constitute the ultimate futuristic extension of the Wyss Institute study.


Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He chairs the advisory board for the Breakthrough Starshot project, and is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021.



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Avi Loeb

Avi Loeb

Avi Loeb is the Frank B. Baird Jr Professor of Science and Institute director at Harvard University and is the bestselling author of “Extraterrestrial”.