Altruistic behavior has long puzzled scientists and philosophers alike; but a recent study from researchers in Israel claims to have found the source of altruism in the unlikeliest of places: our guts.

“The evolution of altruistic behaviour, which is costly to the donor but beneficial for the recipient, is among the most intriguing questions in evolutionary biology,” the researchers state in the study’s abstract.

The body of research into the power of microbes is growing all the time, with the effects of microbes in our gut on our neurotransmitters and hormones already well-established, particularly in the case of the development of the rabies virus where the host becomes far more aggressive than usual.  

Ohad Lewin-Epstein, Ranit Aharonov, and Lilach Hadany are the researchers at Tel-Aviv University in charge of this particular study, published in Nature, and believe their model even suggests that microbes could outweigh genetic factors in influencing our behaviour. 

Their theory centers around one simple fact; humans are social animals, so while on the surface being kind doesn’t necessarily benefit us, it does allow our microbes the opportunity to spread to another host given that we cohabitate, share food and often groom ourselves in close proximity to one another.

The team produced a digital model based on ‘the prisoner’s dilemma’ wherein a certain percentage of the population possessed the altruistic microbes and the rest didn’t.

‘The prisoner’s dilemma’  is a game theory developed in 1950 to demonstrate why two completely "rational" individuals might not co-operate even if it appears that it is in their best interests to do so

© Christopher X Jon Jensen (CXJJensen) & Greg Riestenberg / Wikipedia

Regardless of the initial percentage that began the model with the altruistic microbes, through the payoff scheme inherent to the prisoner’s dilemma, they were able to establish that the microbes would always spread throughout a given population sooner or later. 

They then tested the microbial model against a variant in which altruism can be encoded genetically by a host. They found that microbial altruism always evolves whereas genetic altruism, while persistent, tends not to evolve and thus self-perpetuate. 

They concluded that microbes may play a far greater role in the evolution of altruistic behavior than previously thought and therefore warrant more research than they have received to date.

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

The next stage in their research will examine the potential effect antibiotics, probiotics and different foods can have on our microbiome and thus our overall behavior.