Ethics of Research involving animals
Extrapolating the results of animal studies to humans: the scientific validity of animal research
General arguments about scientific validity
10.27 Some of those who oppose animal research on scientific grounds argue that anatomical, physiological, cellular, biochemical and other differences between humans and animals seriously compromise most extrapolations of results from animal studies to humans.1 A few take an absolutist position. They claim that the differences between humans and animals are so substantial as to make any such extrapolation scientifically meaningless, and that the only sufficiently reliable model with which to study humans are humans. Others argue that clinical observations in humans often reveal medical discoveries, which are then subsequently ‘validated’ in animals (see paragraph 2.4). The conclusions drawn from such a position are that (i) most animal research has proved to be dangerous and misleading and (ii) the use of animals should be abandoned and replaced by other methods such as cell and tissue culture, computer-simulation research, computer-simulation research, or postmortem research. There are frequent claims that these approaches are more reliable, especially if they use human-based models or data. Some of these views were illustrated by the following responses to the Consultation:2
‘The only reliable model for a human is a human.’
Anonymous
‘It is not proved that animal research is a superior route to information. Transference of results can, and has, proved misleading.’
International Primate Protection League UK
‘…if, as we maintain, animal experiments do not advance human medicine, there is no issue other than the fact that conducting animal experiments is absurd, is unethical for both animals and people and should cease immediately.’
Europeans for Medical Advancement
10.28 Other opponents of animal research do not take such an absolutist stance, believing that, in at least some cases, animals can be used as scientifically useful models for humans, although they may remain critical of any animal experiment on ethical grounds. Like those who adopt an absolutist position, these opponents also tend to argue that non-animal approaches yield results that are more relevant for humans. They assert that greater efforts should be made to develop and implement non-animal approaches as replacements for animal studies.3 Whatever their position in the spectrum, all opponents are also likely to assert that researchers over-state the predictive value of animal experiments.4
10.29 Those questioning the scientific validity of animal research employ a range of examples to support their general arguments.5 These include:
i) specific cases in which it is claimed that animal models have failed to predict effects in humans and/or in which research using animals has not led to clinical benefits;6 ii) more-general examples of areas of research in which it is argued that preventative medicine and public health measures have made a greater contribution to improvements in human health than vaccines, treatments or other interventions whose development involved the use of animals;7 iii) cases in which it is claimed that animal experiments have not benefited human health because the objectives were not original, not relevant, not current or not worthwhile, or because the experimental design was poor.8
10.30 Most of those who argue that animals can provide scientifically valid ‘models’ for humans do not contend that every use of animals yields immediately useful results, nor that the use of animals is always the most suitable approach. But they firmly refute the claim that cases in which animal experiments can be regarded as flawed are sufficiently widespread and indicative of a common, underlying difficulty such that the concept of animal research as a whole is flawed. The examples given in Chapters 4–9 support this view.
10.31 We have examined arguments about the implications of the evolutionary relatedness of humans with other animals (see Chapter 4). We concluded that continuities in the form of behavioural, anatomical, physiological, neurological, biochemical and pharmacological similarities provide sufficient grounds for the hypothesis that animals can be useful models to study specific aspects of biological processes in humans, and to examine the effects of therapeutic and other interventions (paragraphs 4.8-4.10). We described a wide spectrum of different kinds of biomedical research activity, between them employing a variety of different kinds of animal model to address a range of different objectives. They included basic physiological studies (Chapter 5), more applied work on human diseases and genetic disorders (Chapters 6 and 7), pharmaceutical discovery and development (Chapter 8), and toxicity testing (Chapter 9). The examples showed that research and testing involving both genetically normal and GM animals has proved relevant to humans and, in combination with other methods such as in vitro and clinical studies, has contributed significantly to biomedical understanding. The cases presented show that there are numerous instances in which extrapolations from animal studies can be made in a meaningful way, provided that the animals involved are sufficiently similar to humans in relevant aspects of the biological phenomenon or disease being studied.
10.32 The examples in Chapters 5–9 also illustrated some of the difficulties involved in extrapolating from animals to humans. Although there has been extensive use of animals in HIV/AIDS research, modelling of this complex disease is difficult, and all of the currently available animal models have limitations. In some cases, promising vaccines have been used successfully in macaques, but have not provided protection for humans. Fundamental differences between the HIV/AIDS disease processes in the macaque model and in humans need to be considered carefully in making predictions from one to the other (paragraphs 6.36–6.37) next page
Footnotes1 The arguments are usually framed in terms of extrapolation from animal studies to humans. In principle, the same arguments
could be applied to extrapolations between different animal species, for example in veterinary research when mice are used
as ‘models’ for pigs or horses. While some of the discussion in this section will relate to both claims, in general we focus on
issues concerning the transferability of data from animals to humans.
2 See, for example, Greek CR and Greek JS (2002) Specious Science: How genetics and evolution reveal why medical research on
animals harms humans (New York: Continuum Publishing).
3 See Chapter 11 for a discussion on the scope and limitations of the Replacement approach.
4 See, for example, LaFollette H and Shanks N (1996) Brute Science: Dilemmas of animal experimentation (London: Routledge).
5 For further discussion, see Animal Procedures Committee (2003) Review of Cost-Benefit Assessment in the use of Animals in
Research (London: Home Office), pp17-34.
6 A variety of such examples are presented in: Greek and Greek (2002) Specious Science: How genetics and evolution reveal
why medical research on animals harms humans (New York: Continuum Publishing); and LaFollette and Shanks (1996) Brute
Science: Dilemmas of animal experimentation (London: Routledge).
7 For example, it has been observed that major reductions in incidence of many common infectious diseases coinicided with
the introduction of clean water and good sanitation in the last century in Europe, before effective vaccination was available.
Another example argument is the possibility of preventing cancers through environmental and/or life-style changes, which
could remove the need for curative approaches. Animal Procedures Committee (2003) Review of the cost-benefit assessment
in the use of animals in research (London: HO), p24.
8 Animal Procedures Committee (2003) Review of the cost-benefit assessment in the use of animals in research (London: Home
Office), p25; For example, the NAVS have cited an experiment performed on ferrets to test the effects of a bacterial toxin.
The bacteria used in this study are a well known cause of food poisoning in humans. The NAVS claim that the data was
already available from human studies, and previous animal studies NAVS (2001) Response from the National Anti-Vivisection
Society to the Animals Procedures Committee consultation paper on the cost-benefit assessment, p29 available at:
http://www.navs.org.uk/download_files/news/Benefit_Assess.pdf Accessed on: 5 May 2005;