Abstract
The evolutionary
approach to the issue of ADHD derives from the assumption
that what is regarded as a pathological phenomenon today was
once an adaptive response to the conditions of life in the
ancestral stages of human development. The paper argues against
this conception on the basis of the clinical picture of ADHD.
The author believes that in the previous "natural"
conditions the ADHD syndrome was even more of a maladaptation
than in the "protective" conditions of present-day
life.
The
Evolutionary Approach to ADHD
On the
pages of this journal (2002;
23 (Suppl.4): 39-45), Charles Crawford and
Catherine Salmon [ 2
] have posed the question of whether some nosological units
considered to be pathological today should not instead be
viewed as the remains of man's purposeful adaptation to life
conditions somewhere deep in our evolutionary history. As
examples they give mental anorexia and the ADHD syndrome (attention
deficit/hyperactivity disorder). For each of the three "disorders"
they find an explanation in evolutionary theory. It is ADHD
that I would like to comment on from the point of view of
a clinical psychologist.
In the
case of ADHD the authors hold that the evolutionary model
may account for the discrepancies in findings traditionally
cited in the literature far better than the symptomatic description
given in DSM-IV [ 1 ], that the evolutionary
model provides a testable hypothesis and that it elucidates
the relationships between health and disease. Their idea is
roughly as follows: ADHD is characterized by transient concentration,
hyperactivity and impulsiveness. In the extreme conditions
of prehistory, man's survival required hypervigilance, rapid-scanning,
quickness to move, hyperactivity and response-readiness. This
would have been an advantage "under the harsh conditions
of the frozen steppe or humid jungle". In different environments
however, with societies becoming more industrialized and organized,
"problem-solving and analytic strategies, restraint of
impulsivity, and the controlled deployment of energies"
would more and more become the order of the day. Still the
population continues to retain the genetic variation of these
original traits, which is reflected in the development of
this kind of behavior. Crawford and Salmon's
conclusion is that what is adaptive in one type of environment
may no longer be adaptive in another.
Symptomatic
Diagnosis versus Etiological Diagnosis
Their
explanation sounds plausible enough and the last sentence
may no doubt be endorsed without reservation. Nonetheless
I can't help feeling that there is something amiss. It will
do no harm if we first make a short review of the story of
ADHD. As a term, ADHD is a relatively recent coinage which
replaced the previous MBD or minimal brain dysfunction (see
footnote) It has
its advocates, but also many critics, myself included, who
point out its disadvantages. To begin with, ADHD, as in fact
any descriptive or symptomatic diagnosis, essentially
says nothing more than what can be seen at first glance. The
International Classification, in order to distinguish a normal
condition from a pathological one, then must look for criteria
that would express that only a certain, especially marked
type of behavior deserves this particular diagnostic label.
It is necessary to section off one extreme (oddly enough not
the other one) from some kind of continuum. But why section
off anything at all in the first place if a certain behavioral
trait represents a continuum distributed in the population
according to the Gaussian curve? The point is that things
are somewhat different! Clinical experience shows that the
extreme described today as ADHD does exhibit certain signs
of pathology.
I still
believe that the term MBD was factual, pertinent and practical,
although it of course could not entirely avoid the difficulties
of delimiting (still normal) function and (no longer normal)
dysfunction. There will always be fuzzy borderlines. However
the term MBD was definitely much easier to use when presenting
arguments in front of the lay public (i.e. even teachers).
It made it possible to explain that we are dealing with a
special (unusual, peculiar) function of the brain, for which
neither school nor the parents or the child alone were responsible,
and so there is no use blaming anyone, but instead we have
to look for help together.
Over a time things have cleared up due to using (as I believe)
the clinical finding, including psychological tests, as a
starting point and due to taking account of etiology and not
only external manifestations. In clinical practice all these
cases of encephalopathy, dysfunction and ADHD obviously look
different from what they appear to be at the taxonomist's
table.
Non-adaptive
ADHD
Under
normal circumstances the "unknown" equals the "dangerous"
for the child. The adaptive mechanism is anxiety which tells
the child (from the eighth month of life onwards), "don't
go there!", "keep close to your mom!", "watch
out for the unfamiliar!" By contrast, children with ADHD
are indifferent to dangers - they are difficult to watch over,
they will rush toward anything "unknown" without
hesitation and this kind of behavior goes way beyond the age
limit of three years when in prehistory they presumably must
have been largely independent so that the mothers could be
free to look after new offspring. Anxiety as a behavioral
corrective does not apply to these children -- they simply
expose themselves to dangers to an exceptionally large degree.
Under natural conditions they would have been caught by a
leopard, bitten by a snake, got lost in the jungle, drowned
in a lake -- and even should they have survived all this,
their reproduction chances were certainly not very high.
In addition,
the "impulsive" child with "transient concentration"
coming under the diagnosis of ADHD is anything but hypervigilant.
On the contrary, the child habitually "acts before he
or she thinks", cannot distinguish a relevant stimulus
from an irrelevant one, "has" to respond to everything
that his senses "come up against", is "addicted"
to stimuli and cannot switch them off, and so is "defenseless"
against them. In other words, he or she is at increased risk
in this respect. Surely enough, this is true of the harsh
natural conditions of our ancestors more than of the civilized
conditions of today.
Hyperactivity does not mean fast and precise advance or fast
and organized retreat -- it involves motor restlessness which
is very difficult to keep under control. Such restlessness
often deserves the attribute "tremorous". It certainly
does not allow one to hide somewhere quietly, to stay silent
and motionless, to wait patiently, etc. By contrast, such
a child arouses and attracts the attention of his surroundings
-- as it no doubt would attract that of a predator. In his
environment such a child acts as a disturbing element and
exhausts those who are there to guard and protect him, even
more those who are to teach him something. Hyperactivity does
not increase motor efficiency, it serves to decrease it. True,
a hyperactive child will climb everywhere, but he will also
fall down from there.
The syndrome
ADHD does not expressly include physical clumsiness today
(which was still part of MBD), but in clinical practice it
is of course in evidence. Actually everywhere we look we find
difficulties: in motor coordination, in keeping balance, in
right-left orientation etc. There are neuropsychological diagnostic
schemes in use to measure this. For many of these children
walking along a narrow path or throwing and catching something
presents an insurmountable difficulty. They are far more prone
to accidents and more frequently subject to medical care than
other children. Moreover, they exhibit difficulties in articulation
as much as in expression and communication - for these problems
diagnostic schemes have also been developed. Physically inept
individuals with communication problems would hardly have
had better chances to succeed in reproduction competition
with skilful, able and communicative people.
Finally,
the syndrome MBD (and, to a perceptibly increased extent,
the symptoms in ADHD children) included strikingly uneven
distribution in the efficiency of individual mental components.
It is as if, for instance, something has dropped out from
the structure of the cognitive abilities, something has not
matured, something has atrophied and, on the contrary, something
has become overgrown (both in compensation and without it).
There are children who cannot cope with verbal tasks, and
there are children who are incapable of understanding any
visual model. The idea of their finding their bearings in
a varied space is absolutely out of question. This certainly
does not sound like an adaptive evolutionary advantage. I
would again regard it as the very opposite. What is far more
likely to be of advantage in the frozen steppe, or a jungle,
or today's big city, is a harmonious distribution of all functions
and not such chaos in abilities and disabilities.
Clinical
experience clearly supports the idea that we are dealing not
only with an end section of a continuum, but with something
"more", i.e. a certain pathology the cause of which
may be looked for in a mild damage of the brain, in genetically
conditioned peculiar functioning of the brain, in short somewhere
in deep biological structures.
Adaptive
ADHD
True,
the world is full of "lively" and "highly active"
children, inattentive children, or children precipitous in
their reactions. We can come across them at every step. That
is a different story, though. Anyone who has seen these children
and ADHD children will never lump them together. The parents
often say that their child cannot concentrate on "anything
for a moment". But when we ask how long the child manages
to play with something, how long he or she can manage to listen
to a story or watch TV, we can see the difference at once.
In one child it is a matter of seconds, in another it is half
an hour, an hour or even longer. At school, even normal "highly
active" children may be a problem, but we have different
recommendations, different advice, different protective and
supportive measures for them than for children with MBD or
ADHD.
These
basically healthy, agile and bright children may well be one
of the "adaptive" genetic variations surviving from
prehistory until today. Why not? But they are not children
with ADHD (i.e. ADHD that deserves its place in DSM-IV),
for although ADHD children are capable of survival and acceptable
social integration in our contemporary refined and "handicap-friendly"
environment, their chances in the prehistoric conditions would
be rather slim. In sum, I think that we may turn Crawford
and Salmon's argument around and say that ADHD is an acceptable
adaptive behavior today, whereas in prehistory it was entirely
non-adaptive.
Conclusion
Why have
ADHD children not disappear altogether over the millennia?
(In fact, their number appears to be increasing.) The answer
is that although this type of behavior is due to genetic mechanisms,
there are other mechanisms at play "over and above"
the genetic factor. These other mechanisms, damaging or adversely
affecting the function of the brain, are constantly with us.
Actually they have been selectively dogging each new human
generation from prehistory until today in much the same way,
I think, as, for instance, cerebral palsy or congenital blindness
and deafness. Also these affections are not just one extreme
of the continuum of human agility or sharpness of hearing
and vision, but involve something "more". In the
Pleistocene period children with such a handicap would have,
more often than today, simply not survived - and if they did,
it was only thanks to exceptional protective and supportive
care for its offspring which human society was so extraordinarily
endowed with in its evolution. At present, however, in our
contemporary cultural environment these children live a relatively
acceptable life on the whole. Compared with children with
severe motor or sensory handicaps, ADHD children's "extra"
burden is relatively small -- but it is not difficult to imagine
that in the Pleistocene period even this small non-adaptive
"extra" was for its bearers considerably greater
burden than is the case today.
References
1.
Attention-Deficit/Hyperactivity Disorder. In: Diagnostic and
Statistical Manual of Mental Disorders, 4th edition, DSM-IV-TR.
Washington, American Psychiatric Association 2000: 85-98.
2.
Crawford Ch, Salmon C. Psychopathology or Adaptation? Genetic
and Evolutionary Perspectives on Individual Differences and
Psychopathology. Neuroendocrinology
Letters,
2002: 23 (suppl. 4): 39-45.
3.
Kucera O, et al. Psychopathological manifestations of mild
children´s encephalopathy. (In Czech) Prague, SZN 1961.
*
In the former Czechoslovakia the MBD syndrome was quite independently
discovered by the pediatrician Karel Macek and introduced
into the technical literature under the name of "mild encephalopathy
in children" by the child psychiatrist Otakar
Kucera [ 3 ] in his 1961 monograph.
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