Bob Kentridge 1995
Comparative Psychology: Lecture 1.
General Overview of the aims of comparative psychology.
One of the aims of comparative psychology is to use insights
gained from the study of psychological processes in different
species of animals to add to our understanding of human
psychology. Any way of achieving this aim must depend to some
extent on understanding the evolutionary relationship between
animals and man. There are, however, two broad ways of
approaching this issue. One way of regarding this relationship is
to think of man as having evolved the most sophisticated
psychological machinery possible. The study of animal psychology
can then allow us to uncover the simpler foundations of man's
psychological processes which are often obscured by his 'higher'
abilities in the direct study of human psychology. This is
probably the assumption that is implicitly made when considering
the results of most psychological research on animals. A more
sophisticated and more biologically correct approach is to consider
how the different evolutionary lineages and pressures of natural
selection of different species give rise to differences in their
psychological abilities. The overwhelming majority of work in
comparative psychology has focused on learning. In addition to
this specialisation of area there has also been an emphasis on two
particular approaches to characterising learning - classical
conditioning and instrumental learning (or operant conditioning).
Finally, two species, the rat and the pigeon, have been studied far
more than all the others put together, perhaps leading to the
simplistic view of 'comparative' psychology I alluded to earlier.
We can see how this situation came about by briefly studying the
historical development of comparative psychology. As this
historical survey approaches the present we will study
contemporary theories of animal learning and consider their
applicability to human psychology. Finally I will briefly discuss
some aspects of the psychology of human memory and will
consider whether animal work sheds any light on them.
An aside about evolution.
Although the extent to which comparative psychology pays heed
to evolutionary theory varies widely we should, nevertheless,
have a firm basic grasp of evolutionary concepts. This grounding
need not go much further than basic general knowledge, it is,
however, worth clarifying a couple of points at this stage. There
is, as I mentioned, a tendency to view work on animal learning as
a way of revealing simple mechanisms upon which our 'higher'
cognitive faculties are based. There is a danger that this may go
hand in hand with a simplistic conception of evolution in which
there is a "great chain of being" with 'lower' organisms at its base,
out of which develop more sophisticated organisms, like rats for
example, leading finally to man at its pinnacle. This is, of course,
Insert a "Great chain of being" image here.
All of the species alive today have been evolving for just as long
as each other. There is therefore little justification for asserting
that any living organisms are 'higher' than others in an
evolutionary sense. It is, however, quite reasonable to assume
that the capabilities of organisms today arose out of the selective
adaptation of their ancestors. So the 'basic' psychological
processes we might hope discover about in comparative
psychology are those of our evolutionary ancestors, not those of
our so-called lower contemporaries. It is hard enough to discover
the true physical structures of extinct organisms from their fossils,
let alone their behavioural and psychological capabilities, so,
although we may be interested in this sort of 'fossil psychology'
we stand no chance of making progress by studying the remains
of our ancestors directly.
Insert a "Tree of evolution" image here.
We can, however, make quite reasonable inferences using a
'taxonomic' approach and making some simple assumptions about
evolutionary histories. If, rather than making the mistake of
assuming a single linear evolutionary history, we think of an
evolutionary tree it is reasonable to assume that more primitive
traits will be exhibited by wide ranges of species - by tracing back
to the earliest common branch point we can estimate the point in
our evolutionary history that such traits must have appeared.
Insert a "Latest common ancestor" image here.
As I mentioned earlier, this is one approach to the interpretation
of comparative data. The other is approach does not aim so much
to discover the evolutionary history of our psychological powers
as to discover how particular environmental pressures in
evolution select for particular psychological or behavioural
adaptations. This approach is much more oriented towards the
study of learning and behaviour in its ecological setting, whereas
the study of fundamental processes in learning ca proceed quite
successfully in quite artificial laboratory settings.
Having briefly outlined the framework in which comparative data
should ideally be viewed (but often isn't!) lets us now begin our
survey of the history of comparative psychology.
Early studies of the mental abilities of animals.
It is reasonable to begin our survey in the time of Darwin since it
is really only with Darwin's 'Origin of Species' (1859), or, more
pertinently, 'Descent of Man' (1871) that people began to admit
that the study of animals could shed light on the abilities of man.
George Romanes met Darwin three years after the publication of
'The Descent of Man' having begun to study the behaviour of
animals with a view to understanding their mental capacities.
Romanes did not carry out experiments on animals, but rather
hoped to gain insights into mental evolution by classifying
observations of the behaviours of different species made by
himself and others and thereby deriving general principles of
animal intelligence. This seems a perfectly sensible approach to
comparative psychology until we examine the kind of
observations Romanes was attempting to classify. We find, for
example, that one of Romanes' observers noted that an earwig,
which she called 'Tom', "crawls up a certain curtain every day
with the apparent expectation of getting its breakfast' since her
two younger sisters were in the habit of feeding it with sugar each
morning. There are many more objective observations in
Romanes book 'Animal Intelligence', together with a few more
ridiculous ones (which he might have included because of the
social status of his observers). Romanes went on to attempt a
classification on the basis of conventional zoological taxonomy of
species in his later books - essentially hoping to use the same
methods that Darwin had used when for the evolution of form
applied to psychological abilities. His first and most widely read
book 'Animal Intelligence' was dominated by observation without
analysis. It amply demonstrates the need for a systematic and
objective approach to gathering data on animal behaviour.
Romanes was by no means alone in his study of animal
intelligence, it was a burning issue in the late 19th century.
Before we start tracing the development of modern theories of
learning, however, a few further examples illustrate the problems
faced by early investigators.
First, there is the issue of instinct. Douglas Spalding also began to
take an interest in the animal behaviour at about the time of 'The
Origin of Species'. He was, however, particularly drawn to the
topic by the work of philosopher's who argued that the mind was
a blank slate (tabla rasa) whose structure was formed by
experience. John Stuart Mill, who was a contemporary of Darwin's
asserted, for example, that even the ability to perceive distance or
spatial relations was not present at birth, but rather had top be
learned by experience. The philosophical position that our minds
are formed by experience is called empiricism, however, debates
over the validity of assertions like those of Mill did not invoke
any experimental, or as we might say, empirical!, evidence, rather,
they stuck to philosophical arguments. Spalding, however,
decided to perform some experiments. He determined, by
comparing the accuracy with which chicks pecked at grain when
they had been raised for the first few day of their lives with their
heads in a hood or free to see, that visual judgement of positions
in space was innate. The first point to note about this is that
Spalding had carried out a well controlled behavioural
experiment. He went on to carry out many more such experiment,
discovering which abilities were innate and which must be
acquired in many different species of animals. We may argue that
instinctive behaviours are not as psychologically interesting as
those which must be learned in response to a changing world -
this is certainly the way in which comparative psychology
developed in the first half of the twentieth century. The study of
instinct, however, demonstrates the care which must be taken
before we can attribute any behaviour to learning. Take, for
example, the behaviour of the digger wasp. Before laying an egg a
female digger wasp will kill or paralyse a caterpillar, then dig a
hole, into which she puts the caterpillar before laying a single egg
on top of it. The caterpillar serves as a food source for the
developing wasp larva. This is quite sophisticated behaviour in
itself, what is even more remarkable is that the mother will
restock the hole with more caterpillars according to the amount
that the larva has eaten. The mother even maintains two or three
young in different stages of development, feeding each according
to their needs. This certainly appears to be very intelligent
behaviour, it is even flexible - the wasp doesn't always feed her
young the same number of caterpillars, but it is purely instinctive.
If we wish to understand the mental capacities of an animal we
must do more than simply study its behaviour, we must discover
the origins of that behaviour.
Another famous example from the early years of animal
psychology emphasises just how difficult this can be. One
consequence of the great interest in animal learning was that
attempts were made to educate animals as one might educate a
child. One of these attempts appeared to be spectacularly
successful. At the turn of the century the German press reported
that a retired schoolmaster, Herr von Osten, had succeeded in
training his horse, known as 'Clever Hans' to answer questions on
general knowledge, judge musical interval and perform simple
arithmetic. Questions were communicated to Clever Hans in
German and he responded by tapping one of his hooves (one tap
for true, two for false, or tapping out the number in answer to
arithmetic problems). Hans' performance was so remarkable that
a committee of German Psychologists, Zoologists and circus animal
trainers were sent to assess it. They found that Hans could
answer questions even when von Osten was absent! At this point
the case was handed over to a student at the Psychological
Institute in Berlin, Oscar Pfungst, for more detailed investigation.
Pfungst carried out the crucial experiment, he established Hans'
performance depended somehow on the knowledge of his
questioner. When Hans answered correctly when asked questions
to which the questioner knew the answer, but his responses were
random when the questioner did not know the answer (although,
of course, other observers must knew the answer and so could
assess Hans' answers). Having established this Pfungst then
systematically removed various sources of information by which
the questioner might be unintentionally signalling the answer to
the horse. By this process of elimination he discovered that
questioners would make very small upward head movements
when Hans' hoof taps had reached the correct answer. During his
training has must have learned that he would be rewarded if he
stopped tapping at this point. Pfungst could in fact induce Hans to
answer questions incorrectly by intentionally making this
If we consider these examples we can see that a taxonomy of
behavioural observation cannot really shed light on the evolution
of psychological faculties unless it is possible to establish whether
a behaviour is learned or innate, and if it is learned exactly what
is that is being learned. The outcome of this at the end of the
nineteenth century was a movement in psychology to eliminate
both anthropomorphic and mentalist explanations of behaviour
and to develop objective methods of studying learning.
We can see from the example of Clever Hans that not only must
we establish whether behaviours are innate or acquired, but we
also need to know exactly what is being acquired and how. In
order to do this a number of highly controllable tasks were
developed for the training and testing of animals as we shall see
in weeks to come.
Most of the historical background was taken from Boakes, R.A.
(1984) From Darwin to behaviourism: Psychology and the minds
of animals. Cambridge: Cambridge University Press. This is an
extremely readable enjoyable book. The digger wasp's behaviour
is described in Warren, J.M. (1974) Learning in vertabrates. In
D.A. Dewsbury and D.A. Rethlingschafer. Comparative Psychology:
A modern survey. Tokyo: McGraw-Hill Kogakusha, which is odd
since its an example of a non-learned behaviour in a non-
vertebrate. Dewsbury & Rathlingschafer is a good source of
serious comparative psychology - if you want to know whether a
sea-anemone or a horseshoe-crab can be classically conditioned