Two primates eye each other, and connect in a way that is both primal and

sophisticated. When you talk to people who work with great apes—myself included—we often describe moments of connection, empathy, and understanding: a juncture when the species barrier dissolves. And yet, while the story seems like describing a meeting between equals, the equality ends when it comes to the letter of the law (4, 5). Chimpanzees can serve as our blood donors, and are genetically more closely related to the average human than human males and females are to each other. Still, an ape does not even have a right to life. Our closest living relative is but a 'thing', with a legal status akin to a piece of furniture. They can therefore be deprived of freedom and bought and sold like any other commodity.

Why this is not right is convincingly illustrated in Planet of the Apes. The French writer Pierre Boulle wrote La Planète des Singes in 1963 (known as Planet of the Apes in USA and as Monkey Planet in UK), and the science fiction novel has since seen numerous cinematographic adaptations (6). The tale centres around three space explorers. They land on an unknown planet—which, in fact, is Mother Earth, just at some point in the future. The planet is inhabited by orangutans, chimpanzees, and gorillas as the dominant intelligent and civilised species, whereas humans are reduced to a savage, 'animal-like' state. The apes hunt humans, capture them in nets, randomly select them to breed in cages, harm them in medical experiments, and display their mounted bodies in dioramas. Thus, the novel turns an all-too-familiar hierarchy of animal-human relationships on its head. That reversal provokes readers and viewers to reflect on a well-known ethical principle: 'Don't do to others what you wouldn't want done to yourself.'

I was able to highlight this point a couple of years ago when 20th Century Fox invited me to London's Soho Hotel, chosen by the film studio as venue for a 'roadshow' to promote another sequel of their Planet of the Apes franchise: Rise of the Planet of the Apes (2014). I was asked to be a podium guest, given my decades-long research on the behaviour and ecology of wild primates (7, 8). I had the pleasure of sitting next to Andy Serkis, famous for computer-aided embodiments in Lord of the Rings and the latest remake of King Kong. Serkis also incarnates chimpanzee Caesar, who leads the apes in a revolt against their human oppressors in a bid for rights and equal treatment.

My podium position allowed me to inform the unsuspecting movie aficionados about serious contemporary discussions, which question the asymmetry in power between humans and other apes. My little speech went roughly as follows: “The scenario in Planet of the Apes where apes hunt, imprison, torture, and kill humans may be science fiction; but on our planet, it is reality that humans catch, harm, cage, and butcher apes. If that doesn't feel right to you, you are not alone. All around the globe, scientists, lawyers, and philosophers are attempting to break down the legal wall that separates great apes from us. What these advocates want is nothing less than the recognition of all great apes as persons.”

In any case, Andy Serkis responded rather enthusiastically when I called upon him to become an ape revolutionary not only on screen, but also in his non-digitised existence. Maybe too much champagne was served. In any case, I handed a pamphlet to the new comrade, with the slightly silly title Brother Chimpanzee, Sister Bonobo. The brochure is part of a campaign to change the legal status of our closest relatives by accepting them as people in what legal practitioners call 'the community of equals' (9).

Primates: A Crash Course

Before we delve into the arguments surrounding the question of whether great apes are just animals, or if they should be given some privileges currently reserved for humans, we need some background in zoological classification. The less enthusiastic reader can skip the following section with its technical terms, as long as two points are kept in mind. Firstly, humans are also primates, so we need to linguistically distinguish 'human primates' from 'non-human primates'. Secondly, humans are also apes, which necessitates a fine-tuned distinction between 'human apes' and 'non-human apes' (10).

In the grander scheme, primates—like rodents, carnivores, and bats—constitute an order of mammals (for the following, see 11). Within the primate order, there are two major groups, or 'clades'. The first are strepsirrhines, the 'wet-nosed' primates, which are mostly nocturnal and benefit from a good sense of smell enabled by a mucous membrane around the nostrils. Strepsirrhines include lemurs and lorises, typically small creatures found in Africa and Asia. All other members of the order belong to the haplorrhines, or 'dry-nosed' primates, which generally rely more on vision than olfaction. These include the smallbodied and nocturnal tarsiers of Southeast Asia. Almost all other haplorrhines are diurnal, representing the normally large 'true' monkeys. Haplorrhines are again divided into two groups. Species native to South and Central America are called New World monkeys (platyrrhines), encompassing the small callitrichids (marmosets, tamarins) as well as capuchin, howler, and spider monkeys. Species living in Africa and Asia are called Old World monkeys (catarrhines), consisting of two groups again: the preferentially folivorous (leafeating) colobines (e.g., langurs, colobus, snub-nosed monkeys) and the more omnivorous cercopithecines (e.g., macaques, guenons, drills, baboons).

The catarrhines also include a sister group to the monkeys, the apes (hominoids). These are again divided into two branches. The small apes (hylobatids) occur in South Asia, comprising the siamang and various gibbons. All small apes are specialised fruit eaters that swing through the canopy, using brachiation as their characteristic mode of locomotion. The great apes (hominids) include orangutans (genus Pongo), the 'red apes' of Sumatra and Borneo, as well as the African gorilla (genus Gorilla), and two sister species, the chimpanzee and bonobo (genus Pan). Humans (genus Homo) belong to the great ape clade too. We also originated in Africa, but have since populated the globe. Even though members of genus Pan and genus Gorilla are hairy knuckle-walkers with moderate to good climbing abilities, genetic data and the fossil record show that Pan shares a more recent common ancestor with Homo. Thus, the sister species chimpanzee and bonobo are more closely related to humans than they are to gorillas or orangutans.

This might seem complicated, so here are the punchlines from 'Great Apes for

Dummies': (i) orangutans live on the islands of Borneo and Sumatra;(ii) gorillas inhabit equatorial Africa; (iii) chimpanzees come in two forms: the "common" chimpanzee, widely distributed in Sub-Saharan Africa, and the bonobo, found only south of the Congo River (bonobos do not feature in Pierre Boule's novel, because they were all but unknown outside the scientific world until the 1980s); (iv) humans originated in Africa before spreading across the globe. The sister species chimpanzee and bonobo are more closely related to humans than they are to gorillas or orangutans.

The Discourse about Nonhuman Personhood

Primatological research is increasingly concerned with ethical considerations. These typically relate to two worries: primate survival in nature, and conditions faced in captivity. Field primatologists have become increasingly pessimistic about the bleak future of natural habitats, as the forested homes of primates are under siege from anthropogenic interventions (12). Widespread destruction is caused by timber extraction, mining, conversion of forests into agricultural fields or oil palm plantations, and human settlements. Hunters kill apes for meat and to obtain body parts for traditional medicine, and babies are trapped to supply the pet market. Cattle herders and human settlers also infect forest animals with diseases such as respiratory illnesses, anthrax, and Ebola. Many researchers therefore supplement their academic interests with efforts to preserve the natural homes of primates.

Primatologists who work with captive subjects are likewise concerned (13). They know that confinement in a zoo, a wild animal park or, worse, a research laboratory condemns non-human primates to a life of restriction, and potentially extreme suffering. While captive primates may have a prolonged life expectancy, their restrained existence is mostly one or boredom, while in biomedical laboratories they are subjected to downright torture. They may be isolated in small barren cages without daylight, living in fear of the next round of experiments, which might involve having measuring equipment stuck into their brains, or being injected with disease-inducing substances.

How are these ethical concerns related to demands to grant personhood to great apes? Importantly, this initiative is not primarily concerned with conservation of species in the wild, nor animal welfare in captivity, nor animal personality (i.e., the growing evidence for intraspecific variability in character and temperament found in taxa as diverse as fish, birds, and mammals). Instead—obvious connections to conservation, welfare, and personality research notwithstanding—the personhood campaign is about animal rights (14, 15, 16).

This legal wrangle takes us into a debate that has raged in Western philosophical and political systems for millennia: Who qualifies as part of the community of equals? Over the centuries, these deliberations have, for example, asked if dark-skinned Africans or Australian Aborigines are human beings, if women should have voting rights, or if gay people should be allowed to marry (17). Arguments surrounding these controversies have defended and, ultimately, questioned discriminatory concepts such as racism, nationalism, sexism, and heterosexism. Advocates of nonhuman personhood confront what seems not only like the next, but also the ultimate, frontier—that of speciesism, where discrimination is based solely on species membership (18). In particular, animal rights supporters challenge the traditional legal status of animals as mere 'things' and the concept that animals can be bought and sold as property.

The peculiar moral status of animals as 'things' has been underpinned by philosophers from Aristotle to Descartes and Immanuel Kant. These scholars denied that animals can think, have consciousness, or possess emotions. Instead, animals were believed to be like machines and to act merely instinctively. Our contemporary laws, that neatly separate us from animals, rest on such time-honoured foundations. Perspectives began to change in the 1960s with the rise of 'cognitive ethology': a new biological discipline suggesting that humans are not unique in having a 'mind'. Field studies with great apes revealed that our closest living relatives form rich social networks, and display mental abilities that allow for cooperation and sharing, for deception and manipulation, and the use of tools involving stones and parts of plants. Some human-raised apes mastered other tasks such as learning sign language or working computer keyboards to communicate with their caretakers.

Certainly, many of the assumptions about animal minds were, and are, controversial. But the growing body of scientific evidence has encouraged animal rights advocates to press their case.

Definitions of what constitutes personhood vary historically and cross-culturally (19). Traditional Western naturalistic concepts (e.g., Descartes, John Locke) tie personhood to traits such as agency, self-awareness, and the ability of mental time travel, i.e., to perceive one's own existence as having a past, present, and future. Many modern thinkers readily ascribe such performance criteria to monkeys and apes—but also to cetaceans (whales, dolphins), elephants, and corvids (crows, ravens). Other contemporary scholars (e.g., Charles Taylor, Harry Frankfurt) reject performance norms and instead embrace significance-based measures of personhood, such as the experience of free will and that things must matter, i.e., rather than one's life being merely a sequence of events, one reflects about what could and should be and cares about whether or not it is fulfilled. Some—albeit, not all—animal researchers believe that nonhuman primates possess such inner feelings.

Other constructs of personhood relate to supernatural beings (e.g., the holy cows of Hinduism; the Trinitarian Christian persons Father, Son, and Holy Spirit), environmental entities (e.g., rivers as integrated, living wholes), or corporations (legal persons, such as the budget airline Ryanair). Thus, what constitutes a person is very much in the eye of the beholder. There is therefore no reason for animal rights advocates to shy away from applying their own definition of a person.

Having painted a broad picture of the animal rights debate (20), let us now be more specific about great apes—not least because objections immediately come to mind. For example, don't rights come with responsibilities? And if apes were to be nonhuman persons, what about other animals, such as elephants, pigs, dogs or, well, jellyfish?

Legal Rights for our Closest Relatives?

The intellectual fault lines about nonhuman animal personhood—in general, and for great apes in particular—can be exemplified by arguments that surround the Great Ape Project (GAP). This campaign was initiated in 1993 by the Australian moral philosopher Peter Singer and the Italian philosopher Paola Cavalieri (21). The GAP calls for some of the privileges currently reserved for human beings to be extended to orangutans, gorillas, bonobos, and chimpanzees. To be specific, the GAP demands right to: (i) life; (ii) individual liberty; and (iii) bodily integrity, also sometimes called 'prohibition of torture', i.e., harmful treatments such as in biomedical experiments. Together, these entitlements would enshrine a status of personhood for these animals.

Why would the world be a better place if some nonhumans had 'rights', instead of merely enjoying 'protection'? Most of us agree with protective regulations aiming to secure the survival of a species, or to reduce unnecessary suffering, such as killing animals via 'humane slaughter'. After all, these measures may help ease our conscience about the harm we inflict on other species. Cynicism aside, experience tells that protective regulations are full of loopholes, because they follow a cost-benefit approach to arrive at 'ethically acceptable' procedures. For example, biomedical companies argue that harmful experiments such as infecting apes with HIV or hepatitis will lead to a net reduction of suffering in humans (22). Of course, scientifically, it would be more logical to not subject 'animal models' to such tests, but to use humans instead. But that is not allowed because humans have a right to bodily integrity, while nonhuman apes (or rhesus monkeys, or cats...) are mere property. Never mind that their level of suffering could actually exceed that of a human.

Clearly, animal rights would be a much sharper weapon in battles related to welfare and conservation. For example, despite long-running protests from the public and NGOs, the Zoo Wuppertal in Germany displayed the chimpanzee Epulu for over thirty-five years in a concrete bunker without access to sunlight—a lamentable situation perpetuated by perhaps well-intended, but ultimately toothless, protection laws. Epulu's is just one of many cases where a court case based on rights would have made a difference for the better. Similarly, concessions for timber extraction and plantations would be much more difficult to obtain if lawyers could argue that the forests in danger of being cut down are inhabited by 'persons', instead of 'just' wild animals.

Finally, there is a certain philosophical beauty associated with the nonhuman rights idea. This is because protective regulations do not operate within a horizon of equality, and therefore remain paternalistic, while the animal rights perspective is one of emancipation and empowerment. Legal entitlements to nonhumans would also be a cultural testimony to the fact that we are products of evolution and thus part of a natural continuum. Still, the GAP faces an uphill battle, as it is criticised on both traditionalist (e.g., 23) and radical grounds (24). In the following, these contra-positions are presented, along with

refutations.

Conservative Objections: Those from the 'Right'

Traditionalist critics—often labelled supremacist or humanist—embody an

anthropocentric approach, asserting that only humans can have rights. However, some taxonomists and geneticists consider the genus Homo ill-defined, and argue that it should be enlarged to include at least chimpanzees and bonobos, who are currently ascribed the separate genus Pan (25). If this happened, then chimpanzees and bonobos would be renamed as Homo troglodytes and Homo paniscus, and thus, by definition, would be humans.

A similar objection states that great apes cannot have 'human' rights. Biologists will be quick to point out the linguistic mistake: some great apes already enjoy legal privileges, as humans belong to this group too. Excluding humans from the animal group of 'great apes' is a wrong zoological classification, as the term would then not be 'monophyletic', meaning it would not include all the members of a group that share a common ancestor. In any case, the GAP does not actually demand 'human' rights for other great apes. Rather, the initiative calls for 'basic' rights that are independent from membership of a particular species.

The GAP has also been criticised because the rights portfolio of humans is not

restricted to life and liberty. It also includes, for example, free speech or a right to education, which nonhuman apes would not be able to take up. The counterargument highlights that not all persons own all rights; for instance, while they possess a right to life, underage humans or prisoners might be deprived of suffrage, i.e., the right to vote.

Other detractors maintain that rights are tied to duties, and that animals cannot

execute such a social contract. However, this argument fails to understand that rights are not acquired, but bestowed. Hence, neonates, Alzheimer patients, and comatose humans all have rights without responsibilities. Similarly, it has been argued that if chimpanzees had rights, they would be punishable for misdeeds. However, certain humans are also exempted from punishment, e.g., children or those classed as paranoid schizophrenics will not be accused of first degree murder. Similarly, allowances could be made for species-typical behaviours, such as when gorilla males kill offspring sired by competitors. Conservative scholars also argue that animals do not demand rights themselves, which would render them legally incapable. However, as is customary for humans who cannot speak up for their own interests, a guardian, custodian, or lawyer could represent them and submit legal claims on their behalf.

The GAP initiative has been labelled as cynical, since it demands rights for animals even though many humans are still deprived of basic rights. However, by this token, the British suffragettes were cynical when they pressed for women's right to vote, since at the time many men did not yet possess voting rights, as these were tied to land ownership. In addition, it is simply unfair to treat somebody unfavourably because others, who are also disadvantaged, are deemed worthier.

Members of the zoo industry might object to GAP demands out of fear for their jobs. No doubt, many animal rights activists would like these institutions closed (26). However, for practical reasons, this is unlikely to happen: thousands of zoo-kept apes cannot simply be released, as there are hardly any 'free' natural habitats left. Even if breeding in zoos were prevented, many decades would pass until, in zoo jargon, 'the herd is managed to extinction'. A no-breeding policy would also conflict with a right to procreate and to interact with younger conspecifics. Importantly, most captive apes are not kept in 'zoos', but in socalled sanctuaries, dozens of which have sprung up in Africa and Asia over the decades.

These refuges take in orphans, confiscated pets, and those who lost their natural homes. These unfortunate creatures will need continued human care. There will therefore be no shortage of jobs for experts such as keepers, vets, and managers of captive 'collections'.

Radicalist Objections: Those from the 'Left'

A second set of objections is generated by radical abolitionists, i.e., theorists who see the stipulations of the GAP as not going far enough (27). These critics accuse the GAP of replacing one type of speciesism with another, i.e.,  substituting anthropocentrism, or humanism, with apeism, or hominidism.

GAP arguments rely heavily on the similarity of cognitive and emotional landscapes between humans and other great apes. Analogous mental traits are embodied by dolphins, elephants, and even parrots. It is therefore not surprising that personhood claims have also been made for these groups of animals. GAP critics assert that this approach amounts to a specific type of speciesism, namely cognitivism—a preference for animals that are mentally similar to humans. This criticism is encapsulated in the classic 1789 quote of Enlightenment philosopher Jeremy Bentham: “The question is not, Can they reason? nor Can they talk? but, Can they suffer?”

Of course, the axiom of extending equality to all sentient beings has its own problems. Who is to say that a jellyfish or earthworm or spider—or, why not a tree?—cannot suffer? But while distinctions will always remain ambiguous and fuzzy, the suffering criterion would render it necessary to enlarge the 'community of equals' to at least include, for example, all kinds of mammals, birds, and fish.

GAP proponents will readily admit that a revised boundary between great apes and other animals is as artificial as the traditional dualism of humans versus other animals. Nevertheless, they defend their approach as pragmatic, taking into account what society at large might be willing to consider at present. Nowadays, many people are willing to ponder the idea that a gorilla can be a person, but fewer would consider the possibility for a mouse or a cat. To speak up for animals we perceive as similar to us is a perfectly normal reaction, regardless of its muddled logic. After all, it is more difficult for us to read the emotions of animals without limbs, or covered in hair or feathers. This is certainly a reason why organisations for species protection, animal welfare, and animal rights so often depict 'smiling' apes and dolphins.

In any case, non-human primates define the sacrosanct divide between humans and other creatures like no other type of animal. If they remain 'on the other side', then so would all other animals; if they can become equals, a slippery slope will open up for other creatures. Thus, its artificial boundary notwithstanding, the GAP may well function as a catalyst for greater inclusivity that has sentiocentrism or painism at its heart, i.e., initiatives that use the experience of feelings or pain as a criterion. Anyhow, the GAP does not compete with or oppose more comprehensive missions. In fact, one of the GAP initiators (Paola Cavalieri) has been lobbying for personhood status for whales and dolphins, and prominent GAP activists (Peter Singer, Colin Goldner, Martin Balluch) adhere to a vegan lifestyle.

A more fundamental critique of the personhood debate is informed by Marxist theory, which holds that capitalism will monetize virtually everything (commodity fetishism). The rights concept in particular is seen to cement capitalism, as it rests on distinguishing those who have rights from those who do not. Arguing that certain organisms are persons with discrete privileges therefore propagates selfishness. Consequently, foregrounding individual personhood fragments societies and the integrated wholeness of biological communities. In contrast, comprehensive liberation, as scholars of ecological feminism maintain, can only be attained at an ecosystem level (28). GAP advocates might respond that, as long as all-inclusive equality remains utopian, pragmatism is going to be more effective than all-or-nothing demands that will likely fail.

What Might the Future Hold?

Even those sympathetic to the cause of nonhuman primate personhood might be pessimistic about its chance of success, as the demands seem so extreme as to not be politically viable. However, history illustrates that anti-discrimination campaigns will often need decades to gather speed.

In fact, intense media coverage, sympathetic judges, and determined animal rights activists have created considerable momentum for the initiative. With this, the Western zeitgeist enters fairly unchartered waters. Similar to the gradual replacement of religious divinism with secular humanism, we may be witnessing the start of a new paradigm. If we want labels, we could conceptualize the new approach as posthumanism, transhumanism or—to use a term invented by English biologist Julian Huxley—evolutionary humanism.

Although falling short of addressing the issue of personhood directly, current

legislation and court cases already reflect a greater awareness of animal rights

considerations (e.g., bans or memorandums on harmful experiments with apes in several EU countries since the 1990s, and in the US since 2014). Various GAP-inspired court cases and petitions were filed with the explicit aim to secure legal recognition as persons for individual nonhuman apes (chimpanzee Hiasl, Austria 2007, see 29; orangutan Sandra, Argentina 2014, filed by Association of Professional Lawyers for Animal Rights; chimpanzees Hercules and Leo, USA 2015, filed by the Nonhuman Rights Project; petition 'Grundrechte für Menschenaffen' to German Parliament, 2015, filed by the Giordano-Bruno-Stiftung).

All these cases did not (yet) succeed, save one. For almost two decades, the orangutan Sandra was held alone in abysmal conditions at the Buenos Aires Zoo; a male partner died long ago, and their baby was taken away. In December 2014, a court in Argentina awarded her the status of 'juristic subject', a cryptic term that makes her a nonhuman person (30). Consequently, Sandra will need to be transferred to a more spacious and accommodating setting.

A small, perhaps too small, victory of animal rights activists? Maybe. But when we reflect on earlier emancipatory processes, they too were often energised by individual cases. Various examples come to mind: Lord Mansfield's freeing of the 'negro slave' James Somerset in the United Kingdom (1772); the verdict against Rosa Parks, who had refused to give up her seat on the bus for a white passenger in Selma, Alabama (1955); the landmark decision on abortion in the US, fought for Norma McCorvey, alias Jane Roe (1973); or the case won in the US by Edith Windsor, who objected that the legal concepts of 'marriage' and 'spouse' only applied to heterosexuals (2013). So, maybe Sandra's case will be another 'crack in the wall', the fissure that will soon lead to the wall's complete collapse.

For seasoned primatologists like myself it is natural to declare that 'we are apes'. That is not a witty remark—it is a fact. But the phrase 'our closest relatives' will remain a shallow platitude if we do not act on it. Demanding basic equality for great apes is the logical extension of a historical trend. Ethical attitudes amongst humans were first restricted to one's own relatives, then extended to clans, later to members of larger societies, and eventually to all people, with the UN's Universal Declaration of Human Rights. Why should we stop short here and ignore the interests of beings that experience suffering and joy in ways very similar to us, merely because they are not human beings? Future generations will likely be perplexed by our rampant speciesism in much the same way that we are now looking at racism, sexism, and heterosexism.

And so, my fellow primates: Isn't it time to stop considering other apes as 'the other', and instead start thinking of them as 'us'?

Bibliography

1 William C. McGrew, The Cultured Chimpanzee: Reflections on Cultural Primatology (Cambridge, UK: Cambridge University Press, 2004).

2 William C. McGrew, “Field studies of Pan troglodytes reviewed and comprehensively mapped, focussing on Japan's contribution to cultural primatology”, Primates 58, (2017): 237–258.

3 Volker Sommer, “Almost Human Rights”, BBC Radio 4, 20 December 2016,

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5 Volker Sommer, “Non-human Primate Personhood”, in The International Encyclopedia of Primatology, ed. Agustin Fuentes (Boston: Wiley-Blackwell, 2018).

6 Pierre Boulle, La Planète des Singes (Paris: Le Livre de Poche, 1963). Deutsch: Der Planet der Affen (München: Goldmann, 1965).

7 Volker Sommer, Schimpansenland. Wildes Leben in Afrika (München: CH Beck, 2008).

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Volker Sommer is Professor of Evolutionary Anthropology at UCL (University College London). He conducts long-term studies on monkeys and apes in Africa and Asia, exploring the ecological roots of social and sexual behaviours. Founder and director of the Gashaka Primate Project, dedicated to research and conservation of biodiversity in West Africa. Volker Sommer is an adviser to the IUCN as a member of the Great Ape Specialist Group and Small Ape Specialist Group. Sommer also serves on the scientific board of the Giordano-Bruno-Foundation—a German-based think-tank dedicated to the promotion of secularism and evolutionary humanism.