Sunday, May 10, 2020

The Darwinian Moral Dilemmas of Infection-Avoidance Behavior in Humans and Other Animals

Shelley Luther was fined and sentenced to seven days in jail when she opened her hair salon in Dallas, which violated Governor Greg Abbott's COVID-19 lockdown orders.  The judge who sentenced her told her that she was selfish for putting her self-interest ahead of the public good.  She responded that she was not being selfish in opening her salon so that she could feed her children, and that her employees also needed to work to be able to afford food for their children.  In response to the public outrage over her punishment, Governor Abbott revised his orders, so that incarceration would not be a punishment for violating his orders.  Recently, he has loosened the lockdown so that hair salons can open.

This illustrates the Darwinian moral dilemmas that arise when animals fighting against infectious diseases face a trade-off between their need for social distancing and their need for social interaction.

As shaped by Darwinian evolution, animals have two distinct systems for defending themselves against infectious diseases.  One is the physiological immune system of the body that detects pathogenic organisms (bacteria, viruses, fungi, and protozoa) that have invaded the body and then targets them for destruction or mitigation.

The other is the behavioral immune system that includes those behavioral strategies by which animals attempt to prevent infectious pathogens from invading their bodies (Schaller 2016).  One of those behavioral strategies is social distancing: social animals who can be infected by social contact with infected individuals can protect themselves by avoiding contact with those individuals who appear to be infected.  But as social animals who naturally benefit from social interaction, social distancing creates a dilemma in which the animal must weigh the health benefits of avoiding infection against the social costs of being isolated from others.  That's the Darwinian evolutionary explanation for the moral debate we are now having over the COVID-19 lockdown.

Humans are not the only animals who engage in social distancing to avoid infectious diseases (Curtis 2014; Hawley and Buck 2020).  Since social insects are densely packed into large colonies, it is easy for contagious diseases to spread through a colony.  When this happens, ants change their behavior to slow the transmission of the disease.  Among some ant colonies, the older ants are assigned to risky jobs foraging outside the nest, while the younger ants stay inside the nest to care for the queen who lays all the eggs and for the developing brood.  If foraging individuals become sick from a fungal infection, they spend more time outside the nest, thus self-isolating themselves, and the indoor workers move the brood farther inside the nest so that they are far away from the foragers (Stroeymeyt et al. 2018).

Bullfrog tadpoles do not swim with other tadpoles that have been parasitized (Kiesecker et al. 1999).  Social lobsters do not share their dens with lobsters infected with a deadly virus (Behringer et al. 2006).  And olive baboons refuse to mate with partners infected by a sexually transmitted virus (Pacienca et al. 2019).

Sometimes animals must balance the need for social distancing against the need for social interaction.  Healthy vampire bats will not groom sick bats, but they will continue to share their food with the sick bats.  It's as though food-sharing is an essential service that must be maintained even when there's a risk of spreading infectious disease.  Moreover, bat mothers are inclined to care for their sick offspring, so that parental care outweighs social distancing (Stockmaier et al. 2020).  Similarly, among mandrills (a kind of monkey found in the African rainforest), healthy individuals will care for their sick family members, but they will avoid sick individuals unrelated to them (Poirotte et al. 2020).

Some animals are so tightly bound to one another in their social lives that they find social distancing too costly, even when it might protect them from infectious diseases.  So, for instance, among the highly social banded mongooses, there is no avoidance of diseased individuals (Fairbanks, Hawley, and Alexander 2015).

We too are such intensely social animals that we cannot flourish--we cannot satisfy our deepest natural desires--without social interaction with our families, our friends, and our larger community of associates.  For that reason, the COVID-19 lockdowns around the world will provoke a natural resistance from people claiming their natural rights to life and liberty.


Behringer, D.C., M.J. Butler, and J.D. Shields. 2006. "Avoidance of Disease by Social Lobsters." Nature 441: 421.

Curtis, Valerie A. 2014. "Infection-Avoidance Behaviour in Humans and Other Animals."  Trends in Immunology 35: 457-464.

Fairbanks, Bonnie, Dana Hawley, and Kathleen Alexander. 2015. "No Evidence for Avoidance of Visibly Diseased Conspecifics in the Highly Social Banded Mongoose (Mungos mungo)." Behavioral Ecology and Sociobiology 69: 371-381.

Hawley, Dana, and Julia Buck. 2020. "Social Distancing Works--Just Ask Lobsters, Ants, and Vampire Bats." The Conversation, April 3.

Kiesecker, J.M., D.K. Skelly, K.H. Beard, and E. Preisser. 1999. "Behavioral Reduction of Infection Risk." Proceedings of the National Academy of Sciences USA 96: 9165-9168.

Pacienca, F.M.D, et al. 2019. "Mating Avoidance in Female Olive Baboons (Papio anubis) Infected by Treponoma pallidum."  Science Advances 5: eaaw9724.

Poirotte, Clemence, and Marie Charpentier. 2020. "Unconditional Care from Close Maternal Kin in the Face of Parasites." Biology Letters 16: 20190869.

Schaller, Mark. 2016. "The Behavioral Immune System." In David M. Buss, ed., The Handbook of Evolutionary Psychology, 1:206-224. Hoboken, N.J.: John Wiley and Sons.

Stockmaier, Sebastian, Daniel Bolnick, Rachel Page, and Gerald Carter. 2020. "Sickness Effects on Social Interactions Depend on the Type of Behaviour and Relationship." Journal of Animal Ecology, February 28.

Stroeymeyt, Nathalie, et al. 2018. "Social Network Plasticity Decreases Disease Transmission in a Eusocial Insect." Science 362: 941-945.

1 comment:

Doug1943 said...

Very interesting! I don't know what guidance we can get from our fellow creatures on this, though!

I think that a lot of the conservative movement has forgotten that government is a necessity, and that sometimes it must do things that restrict our liberty, such as ordering a blackout if having your lights on at night could silihoute ships to Nazi submarines. War, and pandemics, are the health of the state, so to speak.

Part of our problem is that the scientific consensus on the effectiveness of various liberty-restricting measures, and the consequences of defying them, is not clear. So even if you want to follow the science, and acknowledge that the state has the right in principle, for the common good, to restrict our liberty -- it's not clear which measures should be followed.