A US-Chinese team of scientists have produced embryos that include human cells and cells of a nonhuman primate, the long-tailed macaque. What are we to make of such experiments? How are we to assess their ethical implications?

Historical precedent

The first thing to note is that this is by no means the first attempt to produce creatures that are a mix of human and nonhuman-primates. Already in the 1920s a Russian scientist, Ilya Ivanovich Ivanov, had attempted to cross human beings and chimpanzees. In a series of experiments in French Guinea he tried to impregnate female apes with human sperm, but without success. One practical problem was that the chimpanzees resisted the artificial insemination procedure. Another was that he had a limited number of experimental animals. They were supplied by hunters who typically captured baby chimps while killing the adults. Indeed, there were serious fears at the time that the species was facing extinction in the wild.

When these initial attempts at crossing chimps and human beings failed, Ivanov asked the colonial authorities for permission to impregnate local women with sperm extracted from a dead male chimpanzee, without telling the women the origin of the sperm. The governor did not object to these experiments in principle but would not allow them to take place in the main hospital in Conakry. Ivanov therefore returned to Russia before he had the opportunity to undertake the second phase of his research. No evidence exists that women were impregnated as he had planned.

It should not be assumed that these experiments were simply the actions of a maverick. Ivanov was sponsored by the prestigious Institut Pasteur in Paris and he also found supporters in America. The leading supplier of apes for research in the USA expressed opposition to impregnating chimps with human sperm because of animal-welfare considerations but was not opposed to impregnating African women with sperm from a chimpanzee. ‘No cross of female chimpanzee with man. Man is too big and, if the cross should be successful, the childbirth would be too painful for the mother. No objection to cross of male chimpanzee with female Homo.’

A catalogue of errors

From an ethical perspective, these experiments and proposals were wrong on many levels. The research participants were not told how their sperm was used and there were no plans to tell the women what they would be carrying. The chimpanzees were taken from the wild, even though endangered, and there was little concern for their welfare. The context and the practical arrangements were colonial and overtly racist. The motivation for the research was not medical benefit but was in part scientific curiosity and in part weapons development. One of the objectives was to produce a race of super-soldiers for Stalin’s army.

It is in the context of this long list of ethical transgressions that the fundamental transgression occurred of seeking to generate a creature of uncertain human-nonhuman status.

The attempt to produce a ‘humanzee’ was an offence against human dignity and against the dignity of procreation. Had such a creature been produced he/she/it would have had a confused identity, sharing some human features but not obviously possessing human dignity. Furthermore, the infant would not be the fruit of a human relationship nor be able to develop full human relationships with both parents. One parent would not be human, and the possibility of a human relationship with the human parent would be compromised or perhaps impossible, depending on whether the infant shared a humanlike rational nature.

The human-chimpanzee hybrid would have been conceived as an experimental subject and would be born without a recognised free and equal human status.

Ethics in the mix

Generating admixed creatures of ambiguous moral status is wrong in principle. However, human-nonhuman combinations could be carried out ethically, where the result is either clearly human or clearly nonhuman, where other ethical concerns of consent and safety are addressed, and where the combination has the potential to provide medical benefits.

For example, pig valves have been implanted into human hearts, bacteria have been engineered to produce human insulin and human cancer cells injected into mice as part of research into cancer.

Even Pope Pius XII, who considered the question of xenotransplantation back in the 1950s did not rule out such combinations absolutely. He only ruled out the transplanting of brains or gonads of other species, for these organs bear on personal and specific identity.

Back to the future

Against this background what are we to make of the recent creation of admixed human-monkey embryos?

The closeness of the species in this case and the early stage of development creates a disturbing ambiguity. It does not seem that the human cells were limited to one organ or tissue and it is not clear how the organism would have developed. Even though these chimeric creatures were destroyed after 19 days, in their short life they already raised the question of how we should regard them. This is important ethically and in relation to legal protection and patentability, for example, European patent law excludes ‘uses of human embryos for industrial or commercial purposes’.

The human cells used were induced pluripotent stem cells produced using a common form of cell found in the body: a fibroblast. It is highly unlikely that the donors of these cells consented to their use in the production of human-monkey admixed embryos. Disregard of the need for informed consent on the part of human participants is a recurrent theme in the history of experimentation involving human-nonhuman combinations.

Since the time of Ivanov, we have also learned more about the emotional sensitivity of nonhuman primates. Ironically, this knowledge has come in part from unethical experiments on nonhuman primates conducted in the 1970s. In a series of studies over many years Harry Harlow and others attempted to induce depression and other forms of human-like psychopathology by deliberately and repeatedly traumatising very young rhesus monkeys.

The human-monkey embryos produced in the current research were not implanted into a macaque. However, female macaques were research subjects, undergoing invasive procedures to extract their eggs. All nonhuman animals are not equal and nonhuman primates have a proximity to human beings not only in evolutionary history but also in the complexity of their emotional lives.

Invasive research on nonhuman primates is not ethically justified for basic research but only where it is necessary to the advance of sufficiently important medical knowledge. It is very difficult to argue that primate research was ethically justified in this case.

The aim of the recent human-monkey embryo experimentation was ostensibly medical as human-nonhuman chimeras are proposed as a potential source of organs for transplantation. However, if nonhuman animals are ever used successfully to grow human organs, the animals used will not be macaques. They will be pigs or other large, domesticated animals. The creation of admixed embryos involving cells from humans and nonhuman primates was, at best, basic research for the sake of scientific knowledge. It was not proximate to any medical product or technique.

When experimentation to produce human-nonhuman admixed embryos was debated in the UK parliament in 2008 it was argued that this research would play a vital role in research into diseases such as Alzheimer’s, Parkinson’s and motor neurone disease (ALS). It was only by making such headline-grabbing claims that scientists secured public support for the creation of human-nonhuman admixed embryos.

However, these claims were media hype. Even before the Human Fertilisation and Embryology Act 2008 came into force scientists had already moved away from admixed embryos as a potential source of stem cells. The overclaiming of benefit or of necessity is itself an ethical concern and it is one frequently found when involved scientists or activists seek to overcome public resistance to contentious proposals such as the creation of human-nonhuman combinations.

Criteria for ethical combinations

Research involving human-nonhuman combinations can be ethical, but only if it satisfies a number of criteria. The research must be necessary for advances in medicine and not only for the sake of scientific knowledge. It must not involve undue risk or burden on human participants nor cruelty to animals used in the research. It must not use primates where less emotionally sensitive species could be used. It is ethical only if all human participants, and especially those donating tissue, have provided specific and informed consent.

In addition to these ethical principles and requirements, the research must also respect human dignity. Full and equal human dignity is the bedrock of many human rights and we need to be able to identify easily the subjects of such rights. It is always wrong deliberately to create beings that have an uncertain or perplexing moral status.

For this reason, there should be an immediate moratorium on the creating of embryos that mix human cells with those of nonhuman primates. Science requires clear ethical boundaries if it is to maintain public trust and an essential moral boundary is that between the human and the nonhuman.

Dr David Albert Jones is the Director of the Anscombe Bioethics Centre, Research Fellow at Blackfriars Hall Oxford, Professor of Bioethics at St Mary’s University, Twickenham, and Vice-Chair of the Ministry...