Sorry mate, you're a monkey…

Many of our legal and moral frameworks are based on natural distinctions. There's an obvious biological difference between humans and animals, embryo and adults, men and women, parents and non-parents, black and white... isn't there? And given that there are differences, it follows that one's moral and legal status might depend on membership of these groups.

As Aristotle famously says, justice means we should 'treat equals equally and unequals unequally'. Biological differences are perhaps the most fundamental basis on which to build the hierarchical frameworks that support our conception of justice along Aristotle's lines. 

And yet, looking back, we see an appalling history of oppression and extermination arising from judgments based on these categories. It was the basis of the eugenics movement that saw the rise of Nazism and the Holocaust in the last century. Aristotle himself believed sincerely that there is an inborn difference between slaves and those who are fit to be their masters. And between men, who are capable of the highest level of human excellence, and women, who are merely inferior copies of men. The relationship between these biological categories and their ascribed moral status is now recognised as having been deeply flawed. Nevertheless, we continue to search for natural answers to moral questions, and to build our legal frameworks on precarious biological claims.

The recent creation of human-monkey chimeras neatly exposes the problems that arise from this tendency to place entities within certain 'natural' kinds and work out their moral status based on this categorisation (see BioNews 1091). The scientists who created the embryos noted that they could perfrom research on them that would not be legally permitted on humans. But on what basis can we say they are not human? 

One approach might be to work out the proportion of animal and human DNA in a chimera. Over 50 percent human, and you get to be classified as human. At 49 percent? Well, sorry mate, you're a monkey.

But it seems ludicrous to think that – of two almost identical organisms – one is designated human, and entitled to full legal protection, while the other, differing in genetic makeup by only one percent, and perhaps identical in terms of capacities and cognitive function, is deemed an animal. Of course we could try to avoid this by stipulating that the difference has to be greater. To count as human you must have at least 60, 70, 80 percent human DNA – or whatever figure we specify. But this, too, is uncomfortable. Any decision to set the threshold here or there is in some sense arbitrary. We could perhaps use some additional biological criterion to justify our placement of the threshold: suppose the 10/90 monkey-human has a brain that generally weighs the same as that of the average human, while the 11/89 version weighs consistently somewhat less. This might serve as an additional justification for setting the threshold at 10/90.

The big problem here is justifying whatever criteria are chosen. If we choose brain weight, this might call into question the rationale for believing that men and women are equals, since women's brains are of course lighter than men's. Even though these are genuine biological differences, one cannot simply assume that they thereby have moral significance. 

It is troubling that although the human/animal dichotomy is so fundamental to our moral and legal frameworks, we lack a coherent explanation of what really makes someone human. Is it DNA? Brain size? Or some other biological feature? Perhaps the problem lies with our reliance on biology itself. In the historical examples above, biological concepts were used as a basis to separate out certain groups and subject them to oppression or extermination. 

If we consider what exactly it was that went wrong in these historical cases, there are two possible answers. Firstly, we might say that the biological claims underpinning the Nazis' and slave owners' reasoning were factually false, and that there are no biological differences between oppressors and the oppressed. 

Alternatively, we might suggest that the problem goes deeper than this. If we argue about which biological claims are factually correct in these contexts, we implicitly endorse the idea that biology itself contains the answers to our moral questions. Rather than look to biology in order to condemn the atrocities of the past, then, we ought to recognise how risky, fallacious and unethical it is to base moral reasoning on mere biological facts. 

As long as mere biological difference serves to justify preferential treatment for some groups over others, we are vulnerable to the possibility that our own traits may be singled out as those that belong to the underclass. It is common nowadays to assume that all humans are equal: they have the same moral status, irrespective of sex and ethnicity for example. The concept of human rights cements this kind of reasoning. We – as humans – are all equally entitled to these rights. As I have shown, what 'human' means, in a world that includes chimeras, is profoundly unclear. But even if we exclude chimeras, it is simply not true that all humans are equal. We are different from one another in myriad biological, and other ways. 

With the creation of human/monkey chimeras, we have a chance to revise our basic assumptions about the relationship between biological traits and moral status. We cannot rely on fixed biological categories to do the moral work for us. If we want to use, kill, create or experiment on certain entities but not others, we need a better basis for making these distinctions.