The-psychobiology-of-aggression-and-violence-Bioethical-implications_2010_International-Social-Science-Journal.pdf

The psychobiology of aggression and

violence: bioethical implications

Jose´ Luis Dı´ az

Introduction

problem of determining whether aggressive

behaviour is innate or acquired. This is a deli-

cate issue because, were there to be a genetic

and biological cause of aggression, it would be

difﬁcult to change this through social learning

and we would be irredeemably condemned to

violence. This view was heavily criticised by the

Seville Statement (Adams 1991), with solid

scientiﬁc arguments be difﬁcult stating that,

far from implying that aggression or violence

were genetically deter-

mined, the behavioural,

cognitive and neurological

sciences showed that biolo-

gical determinism is much

less prevalent, which not

only allows but obliges

us to consider social ele-

ments as necessarily rele-

vant in their processing and

expression.

This study is a sum-

mary of certain psycho-

biology research topics

that are relevant to aggres-

sion and violence and to

the development of bio-

ethical arguments. Special

attention is given to the

problem of distinguishing

innate from acquired

aspects of aggressive beha-

viour, the ethological understanding and deﬁni-

tion of aggression, the biological basis for this

behaviour and the link between emotions and

aggression. The aim is for this platform to be

used eventually to develop a bioethical argument

Bioethics is concerned with the ethical andmoral

aspects of life-related phenomena covered by

biology and medicine. Topics such as the use of

animals in harmful experiments, human respon-

sibility within ecosystems, abortion, euthanasia

or the use of stem cells for scientiﬁc and

therapeutic purposes have been widely analysed

and debated. Potentially, the ﬁeld is very wide

and can be applied in other

socially relevant ways. One of

these is the bioethical implica-

tions of cognitive and beha-

vioural science, particularly

the subject of aggression and

violence. The relevance of this

subject is clear, as very differ-

ent moral and legal responsi-

bilities may apply depending

on whether aggression and

violence are forms of beha-

viour that are innate or

acquired, deliberate or auto-

matic, understandable and

justiﬁable based on causes,

or how they relate to certain

neurological and psychiatric

conditions. In this and the

above-mentioned topics, bio-

logical research and natural

science theories are basic

ingredients for reﬂections, arguments and deci-

sions concerning ethics.

One of the original and recurring themes of

analysis in behavioural science (in terms of the

social role of aggression) is the apparent

Jose´ Luis Dı´ az is in the Department of the

History and Philosophy of Medicine,

Faculty of Medicine, National Autono-

mous University of Mexico. The main

focus of his research interests is psycho-

biology or the study of the biological and

cerebral basis of the mind and behaviour.

His studies have covered neurochemistry,

psychopharmacology, ethnopharmacol-

ogy, ethology, the mind–body problem

the nature of consciousness, cognitive

science and epistemology. His recent

publications include H. Vargas-Pe´ rez, L.

Sellings, T. Grieder and J.L. Dı´ az, (2009)

Social dominance rank inﬂuences wheel-

running behaviour in mice in Neuroscience

Letters, 457 (3), 137–140; J.L. Dı´ az, (2007)

La conciencia viviente.M´ xico: Fondo de

Cultura Econo´ mica; and J.L. Dı´ az (2009)

The legacy of Cajal inMexico in Revista de

Neurologı ´ a, 48 (4), 207–215.

Email: jldiaz43@gmail.com,

www.joseluisdiaz.org

ISSJ 200–201 r UNESCO2011. Published byBlackwell PublishingLtd., 9600GarsingtonRoad, Oxford, OX4 2DK, UKand 350Main Street, Malden,MA02148, USA.

234

Jose´ Luis Dı´az

founded on an empirical basis. The study does

not tackle the issue of genetic inﬂuence on

aggressive human behaviour, as this subject has

been widely analysed by the renowned Nufﬁeld

Council on Bioethics (2002) in its report Genetics

and human behaviour: the ethical context.That

exhaustive and critical report makes it clear that

genetic and acquired factors are involved in the

expression of aggressive behaviour and that it is

methodologically difﬁcult to distinguish between

them. The present study will thus be limited to

certain behavioural, cognitive and physiological

aspects of aggression. Before entering the sub-

stantive part of the study, the concepts involved

must ﬁrst be deﬁned.

The term violence tends to apply to any

event that occurs with unusual force, such as a

typhoon, earthquake or train collisions. In terms

of social interactions, we talk of violence when

the following two conditions are fulﬁlled: the use

or application of intense aggression that inﬂicts

serious damage to people or their property and

the use of this damaging force against what is

considered natural, fair, moral or legal. In both

senses of an attack that disturbs the natural state

and violates a social rule, the application of the

term would appear to be limited to human

beings and a distinction should therefore be

made between violence and aggression in terms

that not all aggression is violent – only attacks that

are harmful or destructive to subjects or objects

and that threaten, weaken or break natural, social

and cultural rules. We will see that certain

incidents in primate groups could be classiﬁed as

violent in some of these ways. To locate and

understand the issue of violence, it is therefore

vital to consider the concept and phenomenon of

aggression. Aggression should in turn be analysed

on the basis of at least two elements: a group of

emotions and a group of forms of behaviour. This

distinction is relevant because the emotions of

anger, fury or rage that often precede and

accompany aggression may or may not trigger

behaviour or actions of directed force that risk

producing or do produce pain, injury, fear or

terror in the individual on the receiving end. For

the moment this is the operational deﬁnition of

aggressive behaviour that will be the subject of a

critical analysis in this study.

Firstly, the subject of aggression is ad-

dressed in relation to an experimental model

that adequately distinguishes behavioural from

biological causes, which is a relevant issue for

ethics. Secondly, the development of the concept

of aggression in behavioural sciences is exam-

ined. Thirdly, the link between aggressive

behaviour and the emotions that tend to trigger

and accompany it (particularly anger and rage)

is addressed in terms of both phenomenology

and neuropsychology.

Aggression and social

dominance in animals:

regrouping by rank

One way of approaching the origin of complex

forms of behaviour such as violence and aggres-

sion is to use experiments to determine whether

the biological variables precede or follow the

social behaviour. This can be achieved using

various techniques, and one that appears rele-

vant to the purposes of this study is the method

of regrouping male mice by dominance devel-

oped by the author during various studies

carried out in the 1980s. The method consists

in creating groups of three mice in which, within

a few days and with varying degrees and

frequency of conﬂict, a relatively stable hier-

archy is established with one aggressive and

dominant mouse and two evasive and submis-

sive mice. It is easy to recognise rank during

attacks and ﬁghts in the cage by simply

identifying the animal that attacks and the

attacked animal that ﬂees or the winner and

loser in a contest. The behaviour and the actors

can be easily identiﬁed, as the repertoire of

attack and evasion behaviour is very well known

in ﬁeld and laboratory rodents thanks to the

classic work of Scott (1966). To identify the

individuals involved in the agonistic interac-

tions, their back fur is marked with one of three

different colours of permanent ink.

Once the ranking has been established and

stabilised it is possible to carry out various

biological measurements on the animals. How-

ever, measuring a variable does not reveal

whether it is the cause or consequence of the

dominant or subordinate behaviour. In order to

establish causality the mice were regrouped

using their rank to form new groups of three

dominant males and three subordinate males by

mixing animals of previously established and

known ranks. After a few days, new dominances

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Bioethical implications of aggression and violence

235

were established in all groups, giving at least

four combinations of successive ranks:

& dominant in the ﬁrst and second grouping

(D-D)

& subordinate in the ﬁrst and second grouping

(S-S)

& dominant ﬁrst, and then subordinate in the

second grouping (D-S)

& subordinate ﬁrst, and then dominant in the

second grouping (S-D)

Thus, if a biological variable is measured in

animals in which the history of dominance is

known, it is possible to establish whether it is a

cause or consequence of the rank and the

associated aggression or ﬂight behaviour. The

domination–subordination relationship is estab-

lished mainly through the display of aggressive

and submissive behaviour, which makes it a

social phenomenon that results from the ago-

nistic behaviour and also regulates it.

This strategy was used to establish that

dominant mice have signiﬁcantly lower cerebral

enkephalin content than the subordinates (Dı ´ az

and Asai, 1990). It is well known that enkepha-

lins are neurotransmitters and modulators

involved in the central nervous mechanisms of

reward and pain. The technique of grouping

mice by rank demonstrated that the methionine-

enkephalin content in the brainstem is much

lower in doubly dominant animals (D-D) than in

the repeatedly subordinate animals (S-S) and

that the level falls dramatically once the

dominant rank is attained by previously sub-

ordinate animals (S-D), while it increases con-

siderably in mice (D-S) that lose the dominant

rank from the ﬁrst grouping to become

subordinate in the second. It is possible to

conclude that behaviour associated with hier-

archical rank (namely, the aggression and attack

involved in dominance and the submission and

ﬂight involved in subordination) may bring

about signiﬁcant changes in the content of

neuromodulators related to pleasure and pain

in the brain. One interpretation of the results is

that the neurological system for pain undergoes

a preventive adaptation and coping mechanism

in relation to the stress of injuries associated

with subordination. Indeed, in these experi-

ments there were a high number of injuries

resulting from bites and cuts inﬂicted upon the

subordinate mice by the dominant animals.

In order to further assess the time dynamics

involved in losing and achieving social domina-

tion, the author carried out other experiments that

were not published at the time. Data from one of

these experiments are provided in Table 1.

Seventy-ﬁve 12-week old male albino

BALB-c mice were divided into 25 groups of

three. Every day the ﬁghts and attacks and the

winners and losers of each dispute were recorded

for 1 hour. The consistent winners were con-

sidered dominant on the ﬁfth day of consecutive

victories. After 3 weeks, hierarchical social

structures were detected in 21 of the 25 groups,

which meant there were 21 dominant mice each

with two subordinate mice (42 subordinate

animals). In the remaining four groups there

was no aggressive behaviour, attacks or injuries.

On day 22 of the experiment the animals were

regrouped into seven groups of three dominant

mice, 14 groups of three subordinate mice and

four groups of non-aggressive mice (third

column of Table 1). Their behaviour continued

Ta b l e 1. Redistribution of groups of three male BALB/c mice based on dominance hierarchy

First grouping (days 1–22)

Regrouping by rank (days 22–43)

Initial Result Regrouping Result

25 groups of 3 mice 21 hierarchical groups 7 groups of dominants 5 hierarchical groups 5 5 D-D

10 S-S

1 non-aggressive group 3 D-N

1 uncertain group 3 D-U

14 groups of subordinates 5 hierarchical groups 5 S-D

10 S-S

6 non-aggressive groups 18 S-N

3 uncertain groups 9 S-U

4 non-aggressive groups 4 non-aggressive groups 2 non-aggressive groups 6 N-N

2 uncertain groups

Final

distribution

6 N-U

Ranks: D, dominant; S, subordinate; N, non-aggressive; U, uncertain rank.

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236

Jose´ Luis Dı´az

Grouping by hierarchy – attack dynamics

Time (days)

Figure 1. Time dynamics of attacks in a study involving regrouping based on dominance rank

to be recorded in the same way. In many of the

new groups there was a new social structure with

a dominant mouse and two subordinates. The

results are presented in the last two columns of

Table 1. New ranks were recognised in ﬁve of the

seven groups of dominant mice, while in the

other two groups the ranks were uncertain or

there were no ﬁghts. In contrast, only ﬁve of the

14 subordinate groups showed structures of

dominance. In six groups there were no ﬁghts or

attacks, while in the other three groups there

were ﬁghts but no winner or dominant mouse

was established. Lastly, in the four groups that

had displayed no aggression in the ﬁrst round,

two groups engaged in ﬁghts but these did not

lead to an identiﬁably dominant animal, while in

the remaining two groups social calm continued

to reign.

These results of regrouping by rank indicate

considerable variability in the expression of

aggression and submission in mice, despite the fact

that they come from a laboratory strain that is over

99 per cent genetically identical. This variability in

behaviour necessarily implies acquired factors of

an epigenetic, learned or circumstantial nature that

depend on the combination of certain individuals

for a dominant rank to be established with a stable

social structure based on the display of agonistic

aggressive and submissive behaviour.

An analysis of the aggression dynamics in

the groups reveals learned factors in aggression.

Figure 1 shows the time of the experiment along

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Bioethical implications of aggression and violence

237

Total

(74)

No.of mice in each category

Figure 2. Weight gain in dominant (D), subordinate (S) and non-aggressive (N) male mice by dominance rank

showing &, initial grouping (days 1–22) and & regrouping by hierarchy (days 22–43)

the x-axis and the attacks are recorded along

the y-axis. In the ﬁrst grouping (days 1–20),

there was little aggression on the ﬁrst day

but it increased and reached its peak on the

ﬁfth day (with an average of 1.4 attacks per hour

for the entire sample and almost six attacks

per hour by the 16 attacking mice). From

that day, the attacks decreased rapidly before

stabilising from day 10, when the groups settled

down into a pattern of one dominant animal and

two subordinates with little detectable aggres-

sion. The attack dynamics were very different

for the grouping introduced from day 21. This

time around, aggression peaked on the ﬁrst

day, with over two attacks per mouse and 30

contenders attacking nearly six times an hour. In

contrast with the ﬁrst grouping, dominance ranks

were already established by the second day and

subsequent aggressions dropped to levels lower

than in the previous period.

The Figure 1b shows the daily average of

attacks recorded for the 75 mice of the sample,

while Figure 1a shows average attacks by mice

that displayed aggressive behaviour. Figure 1a

shows that the number of attacking mice is

above average. The vertical bars in each group

represent the standard error.

These data point to several conclusions in

terms of the innate or acquired nature of social

aggression and dominance in mice with practi-

cally identical genomes. The ﬁrst conclusion is

that this behaviour has a strong learned compo-

nent, demonstrated by the exponential and rapid

aggression dynamic in the groups made up

of experienced animals, compared with the

dynamic in the inexperienced ﬁrst grouping.

The formation of social structures was much

more rapid and efﬁcient in the second grouping,

and aggression plays a stabilising roles as group

stability is higher when aggression is established

more efﬁciently and with lower stress and injury

costs in implementing andmaintaining the social

structure.

Another interesting variable was body-

weight, as measured once a week. Figure 2 is a

histogram of gains in bodyweight in grams

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