 7. Personality in Animals  185
tween personality and subjective well-be -
ing predated the emergence of humans and 
human societies. This study thus led to a 
search for explanations that would hold 
across humans, chimpanzees, and possibly 
other primates. One possible explanation 
put forward was that common genes were 
responsible for some aspects of personal -
ity (the dominance dimension in this case) 
and subjective well-being. This notion was 
initially supported by a quantitative genetic 
study of chimpanzees (Weiss, King, & Enns, 
2002) and later by quantitative genetic stud -
ies of personality and subjective well-being 
in humans and orangutans (see Weiss & 
Luciano, 2015, for a review). A recent ge -
nomewide association study yielded results 
consistent with these earlier studies (Weiss 
et al., 2016). In brief, a common set of genes 
that give rise to individual differences in 
both personality and subjective well-being 
may have existed prior to human evolution.
Studies of personality in other species are 
also informative for those who seek to ad -
dress why people with certain personalities 
tend to suffer from poorer physical health 
(Deary, Weiss, & Batty, 2010; Strickhouser, 
et al., 2017). Many mechanisms have been 
proposed, but those that predominate in 
the literature posit that human behaviors, 
such as dietary choices, substance use, and 
physical activity, are responsible (Deary et 
al., 2010). Studies of nonhuman animals, 
however, suggest that the mediation models 
favored in much of the human literature may 
provide only a partial picture of how per -
sonality translates into health. For example, 
a meta-  analysis of studies comparing multi -
ple species revealed that species with higher 
boldness and higher exploration (i.e., traits 
that roughly correspond to low neuroticism 
and high openness, respectively) live longer 
(Smith & Blumstein, 2008).
Studies of personality and health by com -
parative psychologists have largely, but not 
exclusively, been of nonhuman primates. 
These studies include two that investigated 
associations between personality and mor -
tality. The first was an 18-year follow-  up of 
zoo- housed western lowland gorillas: higher 
extraversion was related to mortality, but 
neuroticism, agreeableness, and dominance 
were not (Weiss, Gartner, Gold, & Stoin -
ski, 2013). The second was a study of chim -panzees housed in zoos, research centers, 
and a sanctuary. Mortality was assessed 7 
to 24 years later. Among males, longevity 
was related to higher agreeableness; among 
females, however, openness was related to 
longer life, but this relationship was tenu -
ous; neither dominance, extraversion, con -
scientiousness nor neuroticism were related 
to longevity (Altschul et al., 2018).
Further studies investigated health out -
comes other than mortality. The authors of 
one such study found that lower aggressive -
ness, lower “mellowness,” and higher excit -
ability were related to morbidity in golden 
snub-nosed monkeys, and that sociability 
was related to higher morbidity in younger 
monkeys but lower morbidity in older mon -
keys (Jin, Su, Tao, Guo, & Yu, 2013). A study 
that examined associations between person -
ality ratings and veterinary records revealed 
that rhesus macaques higher in confidence 
and anxiety were less likely to be injured; 
there appeared to be no association between 
these personality dimensions and illness or 
between injury and the four remaining di -
mensions, those being activity, openness, 
friendliness, and dominance (Robinson et 
al., 2018). Finally, experimental studies have 
demonstrated that in rhesus macaques, some 
common factor or factors underlie personal -
ity traits related to sociability and immune 
system robustness, and that these effects 
tend to show up in unstable social environ -
ments (see review by Capitanio, 2011).
These and similar findings (see Mehta & 
Gosling, 2008, for a review), and especially 
findings in captive animals whose diets are 
managed, whose health is monitored, and 
who receive treatment for health conditions 
that arise, suggest that studies of human 
personality and health may benefit from 
searching for mechanisms that can explain 
these associations in humans and nonhu -
mans. Differences may be informative, 
too. For example, the study by Altschul et 
al. (2018) that did not find an association 
between conscientiousness and longevity in 
chimpanzees was based on captive samples. 
This means the diets of these chimpanzee 
subjects were controlled, they received regu -
lar health checks, and preventative measures 
and interventions were administered. All of 
this strongly supports the view that the rela -
tionship between conscientiousness and bet -