Sir

In your Opinion article “Rights, wrongs and ignorance” (Nature 416, 351; 2002), you urge scientists and lawyers to challenge the arguments for the basic rights of great apes and other non-human animals that I made in my books Rattling the Cage (Profile Books/Perseus; 2000) and the forthcoming Drawing the Line (Perseus; 2002). You say that some cognitive scientists will challenge my interpretation of the scientific evidence. But others will not. Those who do will find themselves boxing not with me, but with many eminent primatologists and cognitive scientists, for it is their interpretations I adopt.

I am more qualified to argue about law. You refer to those who claim that only beings able to assert rights can have them, so therefore neither young children nor non-human animals can have rights, but should instead be protected. Presumably you would extend this argument to any human beings unable to assert their rights. Yet even the philosopher Carl Wellman, a major proponent of that idea, calls this extrapolation monstrous. Unlike claim rights, such immunity rights as bodily integrity and freedom from slavery can belong to human children, infants, the very retarded, the profoundly senile and the insane. And thank goodness for that, as it is the weakest humans who are in most need of legal protection from exploitation.

You challenge my argument that the precautionary principle, a staple of environmental law, should encourage judges and legislators to recognize basic rights for some non-human animals, and say that the “immense benefits of biomedical experimentation for human health” should be factored in. This misunderstands both my argument for the basic liberty rights of non-human animals and the precautionary principle itself.

I say that a minimum level of autonomy — the abilities to desire, to act intentionally and to have some sense of self, whatever the species — is sufficient to justify the basic legal right to bodily integrity. I call this level “practical autonomy” and maintain that a creature who demonstrates it, whether an adult chimpanzee, bonobo, gorilla, orang-utan, Atlantic bottlenosed dolphin or human, is entitled to this basic legal right. One may reject my premise. But I argue that this rejection on utilitarian grounds undermines the foundation for most basic human rights. We don't enslave people or deprive them of their right to bodily integrity because we think we will benefit if we do.

The precautionary principle comes into play when one is not as sure as one would like that a being has practical autonomy. The strength of that being's claim to bodily integrity turns on how uncertain we are. I argue against both stringent and loose applications of the precautionary principle to the question of which non-human animals are entitled to basic legal rights.

Under the moderate application I urge, African grey parrots and African elephants are entitled to basic rights. Based on what is known, dogs and honeybees are not. But who knows what exciting breakthroughs tomorrow's research may bring?