The issues of generalising results from animal studies.
by Research Methods & Statistics
Dog owners often look like their pets – but does this mean they are the same?
Some psychologists choose to conduct research on non-human animals for numerous reasons. It is a well believed phenomenon that human beings and non-human animals have high enough similarities in terms of physiology and evolutionary past which justifies drawing conclusions from one species onto the other. Research using non-human animal subjects is extremely common within many areas of psychology for example; addictive behaviours (Caine et al, 2007)1, aggression (Raleigh et al, 1991)2, biological rhythms (DeCoursey et all, 2000)3, classical conditioning (Pavlov, 1927)4, eating behaviour (Zhang et al, 1994)5 and operant conditioning (Skinner, 1947)6. For example, several theories of behaviorism were established from experiments carried out on animals as researchers were able to gain a high level of control and objectivity. Pavlov first discovered the concept of classical conditioning (or pavolvian conditioning) whilst experimenting on the salivation reflexes in a non-human sample of dogs. In his experiment, Pavolv reported that dogs salivated as a direct response to stimuli associated with food such as a bowl as well as the unconditioned stimuli itself (food). This initiated the development of his ground breaking study which involved pairing a bell (neutral stimulus) with the food (an unconditioned stimulus) to produce a salivation response to the bell when presented alone (Pavlov, 1927).
Additionally, Skinner developed his Skinner box in order to systematically investigate the concept of operant conditioning (the basic process by which operant learning occurs). Within his experiment, animals performed such behaviors as pecking desks (in pigeons) and pressing control levers (in rats) which then resulted in differential reinforcing or punishing consequences. From such research Skinner concluded that these consequences (e.g. reinforcement and punishment) help shape human behavior and are strong predictors of behavior shown by humans (Skinner, 1947). Such research findings have been generalized to the human population and have contributed to theories of human behaviour and ultimately led to the development of several very successful behavioral interventions such as applied behavior management which is frequently applied within clinical psychology. The behavioural theory has been applied to several psychological disorders such as depression, schizophrenia and obsessive compulsive disorder (OCD). Using classical conditioning, OCD is explained by a particular neutral stimulus becoming associated with anxiety (Mowrer, 1960)7. Due to the initial study involving animals by Pavlov, other researchers have built convincing explanations of human behaviour and behavioral interventions. In the case of OCD the behavioural therapy of Exposure and Response Prevention (ERP) was introduced. ERP has shown to be an effective treatment for OCD with between 60-90% of patients improving from this therapy (Albucher et al, 1998)8. Such high effective rates (Foa & Kozak, 1996)9 in shaping human behaviour justify generalizing results from animal experiments on to humans. However, this therapy is not effective and appropriate for all patients (Gerhuny et al, 2002)10.
Many theorists have criticized both the practical and methodological procedures of animal research and many refer to the issue of generalizability. In other words, generalising the results gained from experimentation from one species to another is extremely difficult, especially findings from animal research onto the human population. Although some believe that the similarities in terms of physiology and evolutionary past justify generalising results on to humans others do not agree. Throughout our evolutionary history every species has had to adapt to gain survival within their own different civilisations and. As a result of such survival strategies each species has evolved their own unique sets and standards of behaviours that will not be useful to other species and may result in an extinction of a particular species. In short, each species has their own unique behaviours to ensure reproductive success.
Koestler (1970)11 has coined the term “ratmorphism” when referring to generalising results from experiments using rats on to human beings. Morphine has been reported to show a calming effect on human beings and also on rats too. In contrast, morphine results in series of mania phases in other species such as mice and cats therefore highlighting the huge differences between species and illustrating that generalising results from different species can be a very serious and intricate issue within the field of research methods.12 Throughout the history of animal testing there have been examples of the serious implications of generalizing results from animal experiments demonstrating the limitations of usefulness and appropriateness within animal research. In the 1950’s Thalidomide was tested on animals and subsequently prescribed to pregnant women to reduce and prevent the symptom of morning sickness13. The studies that tested Thalidomide using non-human samples such as rats, cats, mice and dogs revealed no harmful effects or signs of toxicity on these subjects and therefore the drug was prescribed to pregnant patients suffering from morning sickness. However, scientists were soon to realize harmful effects of generalizing results from animal research and subsequently prescribing the drug to human beings as approximately 10,000 babies were born with severe birth defects such as phocomelia (the abnormal or stunted limb growth) due to Thalidomide.
In the recent times, animal testing has often been used as what is known as a precursor to human clinical trials. In biological terms there are significant brain differences between humans and non-human animals. Studies have shown that mice and rats have a smaller neocortex to brainstem volume ratio. In primates, the neocortex is slightly bigger; however there are significant differences in the proportions in human beings.14 Thus, these differences in neurology suggest that research findings in an animal brain cannot be automatically generalized to human brains. An in-depth understanding and awareness of the limitations of generalizability is extremely important, if not vital, to researchers looking to extend the results gained from animal studies to humans.
The issue of low ecological and external validity of experiments carried out in a laboratory setting is not only proven tricky with research on humans, it is just as much as an issue with animals. An animal’s behaviour when caged in a laboratory, in a very artificial setting, is bound to be very different to the behaviour the animal shows in the wild and in its natural habitat. In experiments, when confined and kept under control (sometimes physical control) animals tend to develop certain abnormal behaviours not shown in a real life setting such as pacing and self-mutilation. Furthermore, certain other behaviours such as mating might possibly become inhibited for example in Giant Pandas. Animals are not used to interacting with humans in the wild however, when in experimental conditions they are often within close physical contact with humans and therefore bound to change behaviour.
An obvious, yet important point to make is that animals do not possess a language. The fact that language is such a huge part of human socialisation and everyday life this sets humans apart from other species. Language allows for a much greater level of communication both between individuals and across cultures and generations. As a result of language, humans are aware of and have extensive knowledge of both the successes and failures of the history of civilisation. In complete contrast, animals have extremely limited cross-cultural transmission between different generations.
All in all, generalisation from animals to humans can be useful as shown by the effectiveness of behavioural therapies yet it is a very dangerous generalisation to make. From such disastrous effects as previously shown by Thalidomide researchers should make an effort to comprehensively understand the limitations of generalizing from such experiments. Experiments have revealed systematic differences in terms of physiology and psychologically between (and sometimes within) species such as the side effects of drugs, brain sizes and attachment styles. On a final note, always be aware that the results from animal experiments may not be applicable to human behavior as due to language we are much more advanced. However, animal studies are sometimes useful.
6 Skinner, B. F. (1947). Superstition in the pigeon. Journal of Experimental Psychology, 38, 168-72.
8, 9, 10 http://books.google.co.uk/books?id=q_Cp_fURG28C&pg=PA216&lpg=PA216&dq=Albucher+et+al,+1998+ocd&source=bl&ots=nhpLZI_rLm&sig=aUCjEuICHHHprZM18q14ciAcw1E&hl=en&sa=X&ei=3mpBT7O3MaKf0QXx7ImPDw&ved=0CCAQ6AEwAA#v=onepage&q=Albucher%20et%20al%2C%201998%20ocd&f=false