Ethics of Research involving animals
The evolutionary continuum
4.8 According to the accepted basic paradigm of evolutionary biology, there is a continuum from simple to more complex organisms. This ranges from primitive forms of life such as Amoeba and other single-celled and multicellular organisms to more complex forms, such as vertebrates. Given what we know about how nervous impulses are transported and processed, it seems highly unlikely that animals without a nervous system, such as sponges, experience pain or suffering, but highly likely that animals with more complex anatomy and behaviour, including vertebrates, do.7 Thus, primate species with higher levels of physiological, and especially neurophysiological, complexity have the potential to experience a given disease or procedure in a more similar way to humans.
4.9 Some people also emphasise the large number of genes that are shared between species. For example, humans share 99 percent of their DNA with chimpanzees and they argue that chimpanzees are therefore ‘almost human’. But knowledge about the percentage of shared DNA has limited application in helping to decide whether or not an animal experiences pain and suffering in ways similar to humans. We also share significant amounts of DNA with animals with which we are less closely related, such as mice (96 percent) and fruit flies (70 percent), and indeed with crops such as bananas (50 percent). Furthermore, the same gene may be expressed in different ways, or for different periods, or interact in different ways with other genes, which means that having genes in common is information that is of limited relevance with respect to assessing welfare.8
4.10 Clearly, however, evolutionary continuities in the form of behavioural, anatomical, physiological, neurological, biochemical and pharmacological similarities provide sufficient grounds for the hypothesis that those animals that possess relevant features are capable of experiencing pain, suffering and distress.9 Evolutionary continuity also means that, on scientific grounds, animals can, in specific cases, be useful models to study human diseases, and to examine the effects of therapeutic and other interventions. Nevertheless, the question remains as to what exactly evolutionary continuity means with regard to the quality of pain and suffering which animals are capable of experiencing. If we use animals as models for diseases that are painful for humans, such as neuropathy, is it not reasonable to expect that the animal models will experience similar pain? We note that for animals to provide valid models, it is usually only important that some element of their bodily processes should be similar to that of humans (see Chapters 5–9).10 They do not always need to show all the typical signs of a disease, but just those relevant to a specific research question. Arguments claiming that all animals used as models for human diseases necessarily suffer ‘…assume that all the systems involved in the detection of pain evolved as a unitary package, which is either present and works in its entirety or is absent and does not work at all… this assumption is not merely implausible, it is wrong. Most complex neural functions can be dissociated into sub-systems and, even in humans, parts of the pain system can be intact while others are deficient. Furthermore, it remains far from obvious that all animals that escape from and avoid damage to their bodies have reflective consciousness.’11 We now discuss in more detail significant biological differences between humans and animals, and differences between kinds of animals. We focus on physiological and neurological development, and describe their importance for welfare assessments.
Footnotes7 See also Chapter 4, footnote 27.
8 The percentage of genes that are shared between two species is not very informative. See, for example, Oxnard C (2004)
Brain evolution: mammals, primates, chimpanzees, and humans Int J Primatol 25: 1127–58. Individual genes can code for more than one protein through alternative splicing. They can also be expressed in a variety of different ways depending on how they are regulated. In addition, a significant proportion of the genome is not in the form of genes and is referred to as ‘junk DNA’. Its functions are thought to be involved in genetic regulation. It is also noteworthy that changes in a single gene alone can be dramatic. For example, chimpanzees and humans became divided from a common ancestor at least five million years ago. About 2.4 million years ago, an important gene mutation occurred in the line that developed into the human species. It has been shown that this mutation resulted in a reduction of the size of the jaw muscles, and may have allowed the brain to expand and develop into its modern human form. See Stedman HH, Kozyak BW, Nelson A et al. (2004) Myosin gene mutation correlates with anatomical changes in the human lineage Nature 428: 415–8.
9 See, for example, Bekoff M (2002) Minding Animals: Awareness, Emotions and Heart (Oxford and New York: Oxford University Press); Goodall J and Bekoff M (2002) The Ten Trusts: What We Must Do to Care For the Animals We Love (San Francisco: HarperCollins); Panksepp J (2003) ‘Laughing’ rats and the evolutionary antecedents of human joy? Physiol Behav 79: 533–47.
10 For example, although humans and mice clearly differ in their appearance, the function of anatomical structures such as tendons is the same in both, and results from studies on tendons in mice can readily be transferred to humans.