August 2020, ScientificAmerican.com 41ing in the face of contagion. In a follow-up study, also
led by Poirotte, mandrills continued to groom certain
close relatives that had high levels of parasites, even
while distancing from other parasitized group mem-
bers. In their 2020 publication in Biology Letters, the
researchers said that maintaining strong and uncon-
ditional alliances with certain relatives can have
numerous long-term benefits in nonhuman primates,
just as in humans. In mandrills, females with the stron-
gest social ties start breeding earlier and may have
more offspring over their lifetimes. Such evolutionary
gains associated with maintaining some social ties may
be worth the risk of potential infection.
The social ties of some group-living animals may
be so critical that avoidance will never be favored, even
when group mates are obviously sick. For example,
work led by Bonnie M. Fairbanks and published in
2015 in Behavioral Ecology and Sociobiology showed
that banded mongooses do not avoid group members,
even when they exhibit clear signs of disease. Banded
mongooses are a highly social species native to sub-
Saharan Africa and live in stable groups of up to 40
family members and nonrelatives. Group members
engage in close physical interactions by resting on top
of one another and taking turns grooming each other
in a quid pro quo manner.
Kathleen A. Alexander of Virginia Tech, another
author on the paper, first noted that many mongoos-
es in her study area in Botswana get visibly sick with
a novel form of tuberculosis that takes months to kill
them. Fairbanks then spent months closely tracking
six troops affected by this disease, observing all social
interactions between troop members. Surprisingly,
healthy mongooses continued to engage in close inter-
actions with visibly sick troop members. In fact, they
groomed them to the same extent that they groomed
their healthy troop mates, even though sick mongoos-
es were far less likely to reciprocate. Distancing from
sick group members may simply not be sustainable in
species where close cooperation with other individu-
als for hunting and defense can make the difference
between life and death.FOLLOWING NATURE’S LEAD
liKe oTher animals, humans have a long evolutionary
history with infectious diseases. Many of our own
forms of behavioral immunity, such as feelings of dis-
gust in dirty or crowded environments, are likely the
results of this history. But modern humans, unlike
other animals, have many advantages when plagues
come to our doors. For instance, we can now commu-
nicate disease threats globally in an instant. This abil-
ity allows us to institute social distancing before dis-
ease appears in our local community—a tactic that
has saved many lives. We have advanced digital com-
munication platforms, from e-mail to group video
chats, that allow us to keep our physical distance
while maintaining some social connections. Other
animals lose social ties with actual distance. But per-
haps the biggest human advantage is the ability to
develop sophisticated nonbehavioral tools, such as
vaccines, that prevent disease without the need for
costly be havioral changes. Vaccination allows us to
maintain rich, interactive social lives despite conta-
gious diseases such as polio and measles that would
otherwise ravage us.
When it comes to stopping novel diseases like
COVID-19, however, we are in much the same boat as
other animals. Here, as in nature, tried-and-true be -
haviors such as social distancing are our best tools
until vaccines or treatments can be developed. But
just like other animals, we have to be strategic about
it. Like mandrills and ants, we can maintain the most
essential social interactions and distance farthest
from those who are most vulnerable and who we
could infect by accident. The success of spiny lobsters
against a devastating virus in the Caribbean shows
that short-term costs of social distancing, while severe,
have long-term payoffs for survival. As unnatural as
it may feel, we need only follow nature’s lead.MORE TO EXPLORE
Infection-Avoidance Behaviour in Humans and Other Animals. Valerie A. Curtis in Trends in
Immunology, Vol. 35, No. 10, pages 457–464; October 2014.
No Evidence for Avoidance of Visibly Diseased Conspecifics in the Highly Social Banded Mongoose
(Mungos mungo). Bonnie M. Fairbanks, Dana M. Hawley and Kathleen A. Alexander in Behavioral Ecology
and Sociobiology, Vol. 69, No. 3, pages 371–381; March 2015.
Ecological and Evolutionary Consequences of Parasite Avoidance. J. C. Buck, S. B. Weinstein and
H. S. Young in Trends in Ecology and Evolution, Vol. 33, No. 8, pages 619–632; August 2018.
FROM OUR ARCHIVES
The Social Lives of the Amboseli Baboons. Lydia Denworth; January 2019.
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