Microbes may encourage altruistic behavior

January 30, 2017 by Lisa Zyga, Phys.org feature

(Left) The payoff matrix and (right) an illustration of horizontal transmission probability of microbes between hosts. Using this model, researchers have found that microbes may induce their hosts to help other hosts, benefitting the microbes and the other hosts, but not always the original hosts. Credit: Lewin-Epstein et al. Nature Communications
(Phys.org)—Why do people commonly go out of their way to do something nice for another person, even when it comes at a cost to themselves—and how could such altruistic behavior have evolved? The answer may not just be in our genes, but also in our microbes.

In a new paper, researchers Ohad Lewin-Epstein, Ranit Aharonov, and Lilach Hadany at Tel-Aviv University in Israel have theoretically shown that could influence their hosts to act altruistically. And this influence could be surprisingly effective, with simulations showing that microbes may promote the evolution of altruistic behavior in a population to an even greater extent than do.

"I believe the most important aspect of the work is that it changes the way we think about altruism from centering on the animals (or humans) performing the altruistic acts to their microbes," Hadany told Phys.org.

It's already well-known that microbes can affect the behavior of their hosts, with a prime example being how the rabies virus increases aggressive behavior in infected individuals. Research has also shown that the microbiome—the community of microorganisms that inhabit our gut—can even manipulate the hosts' social behavior by infecting neurons and altering neurotransmitter and hormone activity.

Against this backdrop, the researchers in the new study have proposed that microbes may induce a person to help others because the close physical contact (for example, food-sharing, co-sheltering, and grooming) increases the transmission of the microbes from one person to another. So when someone does something nice for us, we are not just the recipient of a kind act, but also of their microbes.

To show that this idea can have a prevailing effect on a population over time, the researchers designed simulations of interacting individuals, some with altruism-inducing microbes, and some without. Then using a prisoner's dilemma payoff scheme, the researchers investigated what happens to this population, its microbes, and its altruistic behavior over many generations.

The results showed that, as long as horizontal transmission (between individuals) of microbes is allowed, altruism-inducing microbes can take over the population, leading to microbe-induced altruism. This result occurs even when only a very small percentage of the initially carries these altruism-inducing microbes. The simulations also revealed that the evolution of altruism is successful because the microbes have a chance to either meet genetically related microbes in the recipient or infect and transform some of the recipient's microbes into relatives.

In a variation of this model in which altruism can also be induced by host genes, the researchers found that genetically encoded altruism does not evolve, but microbe-induced altruism continues to evolve whether or not genetic factors are present. Further simulations showed that, although there are some cases in which altruism encoded in genes can persist, microbe-induced persists more often. Overall, the results suggest that microbes may play a dominant and previously overlooked role in the evolution of altruistic behavior.

If microbes do exert such large sway on altruistic behavior, then it raises other intriguing questions, such as whether antibiotics, probiotics, and foods affecting the microbiome may influence the of their hosts. In the future, the researchers plan to address these possibilities, as well as to test the theory.

"We are now collaborating with experimental biologists in order to empirically validate the predictions of our theory," Hadany said.

Explore further: Study reveals some secrets of how microbes and their genes traverse the globe

More information: Ohad Lewin-Epstein, Ranit Aharonov, and Lilach Hadany. "Microbes can help explain the evolution of host altruism." Nature Communications. DOI: 10.1038/ncomms14040

Related Stories

Not all altruism is alike, says new study

April 30, 2012

(Phys.org) -- Not all acts of altruism are alike, says a new study. From bees and wasps that die defending their nests, to elephants that cooperate to care for young, a new mathematical model pinpoints the environmental conditions ...

Being altruistic may make you attractive

October 14, 2008

(PhysOrg.com) -- Displays of altruism or selflessness towards others can be sexually attractive in a mate. This is one of the findings of a study carried out by biologists and a psychologist at The University of Nottingham.

Recommended for you

Earth's deep mantle flows dynamically

March 25, 2019

As ancient ocean floors plunge over 1,000 km into the Earth's deep interior, they cause hot rock in the lower mantle to flow much more dynamically than previously thought, finds a new UCL-led study.

Scientists solve mystery shrouding oldest animal fossils

March 25, 2019

Scientists from The Australian National University (ANU) have discovered that 558 million-year-old Dickinsonia fossils do not reveal all of the features of the earliest known animals, which potentially had mouths and guts.


Adjust slider to filter visible comments by rank

Display comments: newest first

Jan 30, 2017
This comment has been removed by a moderator.
4.5 / 5 (8) Jan 30, 2017
Can we inoculate conservatives,Republicans with altruism?
2.1 / 5 (7) Jan 30, 2017
Careful, liquid, I got "moderated" for the same idea.
not rated yet Jan 30, 2017
Strong immunological responses are acutely associated with positive emotions which is an old premise of psychoneuroimmunology. For example, "Stress affects the balance of bacteria in the gut and immune response" according to scientists from Ohio State University and Monika Fleshner, Professor of Integrative Physiology at the University of Colorado.

According to a study in Neurogastroenterology & Motility, when they examined the animals' brains,
they found that: "these differences in behavior were accompanied by alterations in the expression levels of several genes in the germ-free mice. ... Bacteria colonize the gut in the days following birth,
during a sensitive period of brain development, and apparently influence behavior by inducing
changes in the expression of certain genes."

Neurogastroenterology & Motility March 2011; 23(3); 255–e119
2 / 5 (1) Jan 30, 2017
This isn't Crazy. Maybe the concept of free will is an effect of microbes too. Or perhaps B F. Skinner was actually a microbe.

5 / 5 (5) Jan 31, 2017
"Or perhaps B F. Skinner was actually a microbe." That's Bacterium Fungi Skinner to you, buddy.
not rated yet Feb 05, 2017
Entire avenues of inquiry open. Such as: does fasting support altruistic microbiomes?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.