Why We Help: Do Our Microbes Make Us Do It?

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by Dr. Elizabeth Mitchell on September 15, 2017
Featured in Answers in Depth


“When she was good she was very very good indeed, and when she was bad she was horrid.”1 Did her gut flora make her that way?

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  • Altruism seems to fly in the face of Darwinian survival of the fittest.
  • Evolutionists usually explain altruism in terms of the advantages it provides to a group or family.
  • Our bodies and those of animals are home to microorganisms with which we interact, more often than not to the betterment of our own health.
  • Based on computer simulations, some scientists report that microbial influence may be responsible for the origin of altruistic behavior.

Altruism—selfless sacrificial behavior to help others—is a mystery to evolutionists. In a truly evolutionary worldview, there must be a naturalistic explanation for all that exists. So how did altruism evolve?

The evolutionist asserts that survival of the fittest—by selecting from an almost infinite array of randomly generated natural options—is responsible for all that exists, ever did, or ever will. And that includes not just the physical bodies of all living things but all of their abilities, instincts, intellects, and behaviors. Morality, in that worldview, is nothing more than the evolved preference of people for certain advantageous behaviors over others. Is morality a mere product of biology, perhaps even of the microbes that live inside us? A group of scientists at Tel Aviv University thinks so. They propose that bacteria in our intestines may be responsible for human altruism.2

Survival of the Selfish, or the Selfless?

Survival of the fittest, along with the supposed random emergence of life and all its components, is foundational to an evolutionary worldview. Survival of the fittest refers to the tendency of those traits that best enhance survival of living organisms—be they bacteria, beans, bears, or boys—to become established in a population. Provided those traits help their owners survive to reproduce themselves, that is.

Evolution is at its core a religion of time, chance, and death. Survival of the fittest is seen as the selective mechanism that “decides” who lives and who dies, who survives and thrives and passes on their genes. Survival of the fittest is consistent with behavior governed by self-interest. So how can evolutionists explain altruism—a tendency toward self-sacrificing behavior for the good of others—if survival of the fittest is the mechanism that supposedly brought all things into existence? Genuine altruism involves strengthening another at your own expense. If everyone diminishes his own chance of flourishing by helping those less fortunate, shouldn’t altruism die out as those who practice it weaken and fade away?

The Evolution of Why We Help

Evolutionists have put forth a number of theories to explain how diminishing an individual’s own fitness for survival could, through natural selection, become an established characteristic in a population. These include “kin selection” and “group selection”—the idea that sacrificing to help others in your family or group ultimately passes on genes that promote production of more sacrificial individuals like yourself. The group grows stronger, even at the expense of altruistic individuals. Kin selection became mathematically codified as an evolutionary model explaining altruism in the 1960s. Known as Hamilton’s rule, this cost-benefit principle predicts that altruism will evolve if the sacrificial cost to do-gooders is less than the benefit to the recipients of the good deeds multiplied by their genetic relatedness.

Another evolutionary explanation for altruism holds that reciprocity—essentially the trading of favors—mathematically adds up to good for everybody in a group. We could call this the “what’s in it for me” principle of being nice.

A few years ago evolutionist Martin Nowak worked out more of the mathematics showing how looking out for number one often means looking out for your neighbor. Convinced that cooperation has been a universal driving force for the evolution of every level of complexity from genes to us, he summed up evolutionary history as a snuggle for survival when he wrote,

This universality suggests that cooperation has been a driving force in the evolution of life on earth from the beginning. Moreover, there is one group in which the effects of cooperation have proved especially profound: humans. Millions of years of evolution transformed a slow, defenseless ape into the most influential creature on the planet, a species capable of inventing a mind-boggling array of technologies that have allowed our kind to plumb the depths of the ocean, explore outer space and broadcast our achievements to the world in an instant. We have accomplished these monumental feats by working together. Indeed, humans are the most cooperative species—supercooperators, if you will.3

Thus, the concept that being good to others, even at your own expense, can be good for you is not new, even among humanistic evolutionary thinkers. What the Tel Aviv team brings to the table is a look at factors outside the individuals in a population that could create and perpetuate a spirit of altruism. They propose that individuals might become altruistic under the influence of their microbiome—the microbes that live in their bodies. “Previous works considered altruism only from the perspective of the host,” says Tel Aviv University evolutionary biologist Lilach Hadany, who led the research. “Where classical models would explain the evolution of altruism under some circumstances, this [could explain the] evolution of altruism under wider conditions.”4

Blame the Bugs

Your body is home to trillions of fellow travelers—bacteria and other microorganisms that make up your microbiome. While some, given that we live in a sin-cursed world, are your enemies, most are not. In fact, God designed them to be your friends. This fascinating world of microbes that God created has remained largely hidden for 6,000 years. Now that DNA sequencing has made it possible to detect and characterize microbes that are difficult to culture, scientists can appreciate the scope of the microbial ecosystems living throughout the world and inside each of us. Could microbes influence how we think and feel? Those questions are the subject of ongoing research.

This fascinating world of microbes that God created has remained largely hidden for 6,000 years.

There is precedent for microbial influence on host behavior in animals. A classic example is the way Toxoplasma gondii infestation attracts rats to cat urine, thereby dooming the rats while giving the Toxoplasma microbes access to the cats in which they thrive and reproduce. And around Halloween, when the new season of popular zombie programs air, we are reminded of a fungal infestation which drives ants to be the “climbing dead,” ascending high in the trees to die and thus becoming aerial distributors for the zombie apocalypse as they rain spores on the population below. (Learn more about these climbing dead in “Zombie Ants and Genesis.”)

Clearly, therefore, microbes can drive complex multicellular organisms to destructive behavior that helps the microbes. Sometimes the benefit to the microbes merely involves making more hosts available without destroying the hosts. For instance, fruit fly larvae are attracted to the scent of chemicals produced by bacteria in their gut. Scientists, who reported this discovery in 2014, suspect the resulting group hug helps the microbes gain easy access to new hosts.5

If microbial hosts could, instead of being destroyed by their parasitic guests, be manipulated to promote group survival through self-sacrifice, might altruism become a defining characteristic of the host species? That is the question the Tel Aviv group chose to investigate. As Berkeley evolutionary biologist Andrew Moeller explains, “Microbes can influence the behaviors of animal hosts, so it is not outside the realm of possibility that microbes could promote altruistic behaviors.”6

Bugs ‘R’ Us?

What has Hadany’s Tel Aviv team found? Their work has been entirely confined to the world of computer simulations, but the math suggests that if a microbe-induced altruism occurs in a population, it could lead to establishment of that behavior in the population without any regard to kinship or relationships between individuals. The microbe-established altruism—based on their model—could become established in the population because the microbes soon inhabit most of its members.

The Tel Aviv model sort of does an end-run around genetics. That leaves open the question of what might happen to the behavior if the microbes die off. Would the Golden Rule go out the window with the bugs? A recent study exploring this question in animals involved treating mice near the time of birth with antibiotics to destroy their indwelling microbes. Microbial destruction resulted in aggressive mice that did not work and play as well with others as the untreated mice. The authors suspect that destruction of microbial gut flora at a critical time in brain development alters neurotransmitter levels, producing these murine sociopaths.7

So if microbes promoted altruism to develop in a population, would elimination of the microbes undo it? Would the population become sociopathic, like the antibiotic-treated mice? If the altruistic behavior is solely a result of the microbial presence and offers no other advantages to the population, perhaps so, the Tel Aviv group suggests.

The Tel Aviv scientists picture the ebb and rise of altruism as a sort of arms race between microbes and host mutations. For instance, Hadany says, “If the host has a mutation that makes it resistant to the manipulation of the microbe, the host could start behaving less altruistically.”8 Microbes multiply more quickly than their hosts, she points out, and because “there are many more microbe generations, the microbes have an evolutionary advantage.”9

On the other hand, Hadany speculates, “A new microbe could evolve, this microbe could spread in the population, and while the microbe benefits, the host also benefits.”10

Microbiomes and Morality

So what is the upshot of all this? Are we nice or nasty because of the microbes that live inside us? Should we be giving the blame or the credit for our actions to the bugs in our bellies? As Hadany says, “Any behavior—I’m now thinking, ‘Is it me, or is it my microbes?’”11

Should we be giving the blame or the credit for our actions to the bugs in our bellies?

Such a question is absurd. First of all, there is no evidence that gut microbes control human behavior. This study involves only a computer simulation of ifs. Secondly, even if microbes can influence the behavior of high-functioning organisms like humans, the microbial presence does not explain the origin of those behaviors.

The thought is that microbes, if they influence behavior, might do so through their influence on various neurotransmitters in the host. Let’s consider therefore, for comparison, other chemicals that influence our behavior, chemicals our own bodies produce. If we jog, the beta-endorphins produced in our brains may give us a surge of pleasure that outweighs the agony of the run, motivating us to exercise again tomorrow. Does that mean we must jog tomorrow? No, we might find it a pleasing option, but we might just as easily choose to be a couch potato instead. Whatever the influences on our feelings—beta-endorphins in our brain or our spouse’s praise—we have the free will to jog or not to jog.

Choice or Microbial Coercion?

Our microbiome is a vital component of who we are. It supports our health in many ways, some only recently discovered. Yet if our gut microbes are ever found producing chemicals that make altruistic behavior feel better, the microbes will still not be responsible for the origin of altruism.

Has our cultural romance with being a self-made man or woman ended? It is astounding that after centuries—actually millennia, about six of them—of man rebelling against God, telling God that we want to make our own decisions, we now rush headlong into a materialistic worldview to the point that we wish to assign both the blame and the credit for being who and what we are to naturalistic causes beyond our control. If we wish to understand who and what we are, to know the origin of all the best and the worst in this world, we need to look to the one unbiased reliable eyewitness account of our history, the history of humanity and of all that is, was, and ever will be, in the Word of God.

Nothing to date has shown that microbes can override the ability of human choice or even overwhelm it the way mind-altering drugs like alcohol and hallucinogenic drugs do. Furthermore, while the structure of the human brain and the connections between the neurons in it may both influence and be influenced by things that happen to us, we still choose how we will act. God has given us that ability.

God created all things, including Adam and Eve, the parents of all humans, good. (See Genesis 1:27.) He also gave them freedom to choose whether to obey him. They chose poorly when they rebelled against their Creator. Their sin—the first sin—left the stamp of a sinful nature on all of us. Acting selfishly in our sinful nature, we override the good image of God with which we were created. The motivations that drive human behavior are complex and must involve the interplay of all that God created us to be and all the toxic influences of our sin-cursed world and our sinful natures. Ultimately God’s Word informs us that, even when we try to do our best, apart from God our efforts are tainted by our sinful nature. “No one does good, not even one” (Romans 3:12).

Though spoiled by our selfish, sinful nature, we still often act altruistically. We may act for the good of others because of love or a sense of duty or just a calculating awareness of “what’s in it for me.” In trying to understand why we sometimes act altruistically instead of becoming a race of uniformly sociopathic people, we may credit our personal psychological makeup, our upbringing, or kinship selection. We may be motivated by the perks of good citizenship, fear of reprisal, or maybe even our microbiomes. But one place we will not discover the origin of our nature is in evolutionary thinking. Evolutionary thinking ignores a part of our history that science cannot objectively observe—the time and method of our creation. God created humans in his image. And we know, through Jesus Christ the Son of God’s sacrificial death on the cross, that God’s nature is truly one of sacrificial love.

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Answers in Depth

2017 Volume 12


  1. From Henry Wadsworth Longfellow’s poem, “There Was a Little Girl.”
  2. Ohad Lewin-Epstein, Ranit Aharonov, & Lilach Hadany, “Microbes Can Help Explain the Evolution of Host Altruism,” Nature Communications 8 (12 January 2017):14040, doi:10.1038/ncomms14040.
  3. Martin A. Nowak, “Why We Help: The Evolution of Cooperation,” Scientific American, July 2012, https://www.scientificamerican.com/article/why-we-help-evolution-cooperation/.
  4. Elizabeth Svoboda, “Can Microbes Encourage Altruism,” Scientific American, July 17, 2017, https://www.scientificamerican.com/article/can-microbes-encourage-altruism/.
  5. I. Venu et al., “Social Attraction Mediated By Fruit Flies’ Microbiome,” Journal of Experimental Biology (2014) 217:1346-1352; doi:10.1242/jeb.099648.
  6. Ibid.
  7. S. Leclercq et al., “Low-Dose Penicillin in Early Life Induces Long-Term Changes in Murine Gut Microbiota, Brain Cytokines and Behavior,” Nature Communications (April 4, 2017) doi:10.1038/ncomms15062.
  8. Svoboda, “Can Microbes Encourage Altruism.”
  9. Ibid.
  10. Ibid.
  11. Ibid.


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