No other primate can boast a geographic reach as vast as that of the Human. We have dominated every terrestrial biome, and have forbidden most competing species to even survive. There is, however, a primate with an extraordinary territory, which spans from the hostile mountains of Afghanistan to the lush rainforests of Thailand. This resourceful ‘Old-World Monkey’ is the Rhesus Macaque (Southwick et al. 1996). The genus Macaca, to which they belong, has an expectedly larger range, which stretches across the breadth of the African and Asian continents. Partly because of this success, however, they have been plagued by humanity since the dawn of the Anthropocene.  

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Rhesus Macaque Macaca Mulatta are the non-human primates, alongside Cynomolgus (Long-tailed) Macaques Macaca Fascicularis and Common Marmosets Callithrix Jacchus, on which the majority of scientific experimentation is done. The 2015 ‘Cruelty Free International’ report showed that across the globe, 158,780 tests using monkeys were conducted. This number is increasing drastically year on year, and according to the ‘US Department of Agriculture’, between 2015 and 2018 there was a 22% increase in the US alone.

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The geographical success of the species can be attributed to several factors, including wide non-divergent genetic variance and their adaptability both socially and ecologically. In fact, they have constantly proven a precedent for adapting to human-impacted habitats (including laboratories), so much so that in many regions, especially Nepal, Sri Lanka and India, they are considered a significant problem. As a result, when their 93–97% genetic similarity to humans (Wang, J., Wang, M., Moshiri, A. et al.) is considered, they provide an ideal subject for experimentation.

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A great insight into the mutual history of Rhesus Macaque and Human can be found in Hong Kong. The region has a current population of around 2000 individuals, and their history is eventful, to say the least!

We can assume that they have historically had a stable population here, with local references from great naturalist Robert Swinhoe as far back as 1866. Sadly, by the 20th century, partly fuelled by hunting as well as habitat loss, Hong Kong's population had been more or less decimated. It was at the turn of the century that the ruling British government decided to reintroduce them. According to local government sources, the story goes that whilst building the large Kowloon Reservoir a considerable number of Strychnine Trees were discovered in the area. Occasionally referred to as the ‘Poison Tree,’ their fruit produces high concentrations of the alkaloid Strychnine, which was once a popular rat poison (and source of murder weapon in popular culture, featuring in Hercule Poirot and Sherlock Holmes novels as well as in Alfred Hitchcock's ‘Psycho’). It had been anecdotally observed that Rhesus Monkeys could happily consume Strychnine fruit and so, to prevent contamination of the reservoir (which was to supply the majority of Hong Kong’s water), a new population was released.

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They did not last long. Following nearly four years of Japanese occupation in the Second World War, they had once again vanished. However, years later, by the early 1990s, they had miraculously regrouped once more, with 600–700 now occupying the area. Numbers are uncertain when hybrids with Macaca Fasciculariss are taken into account; however, the ‘World Wildlife Fund’ survey of 1992 estimated at least 50% to be pure Macaca Mulatta. There is little agreement on their origin. It is possible that they are migrants from the nearby mainland China province of Guangdong, or escapees.

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Sadly they face yet another problem. Since the rise in popularity of Hong Kong’s country parks as tourist destinations, there has been a considerable issue with people feeding the Macaques. This popular activity has been largely cracked down on in recent years; however, the lingering generational perception of humans as providers (whether willing or not) of snacks has left a lasting legacy. This has led to the Macaques encroaching increasingly on the nearby city, as well as a relative boom in their population. To counter this, local authorities have enacted ruthless sexual sterilisation programmes. The recommendation from Hong Kong’s ‘Environment and Ecology Bureau’ was to sterilize 100–200 between 2024 and 2028. The project has in fact been in force since 1999, and by the end of 2022, 1,937 monkeys had fallen victim.

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My time with various colonies of Rhesus Macaque across southern China has given me a deep fondness for the species. They can be vicious to each other. A term commonly used to describe their hierarchical society is “despotic”. At the same time they demonstrate moments of pure compassion as well as endlessly charming silliness. Compared to other more docile primate species they are incredibly entertaining to spend time observing.

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There was an occasion, by Kowloon reservoir in fact, that I watched a pair of adolescent males bouncing up and down furiously on a branch in an attempt to make a third loose balance. They failed, and a vicious fight ensued. The screeches which erupted seemed to attract comrades from far and wide and the fight was soon a battle! In a more tender moment, in the broadleaf forests of Guangdong, I observed a mother loafing along, infant clinging to her underbelly. She reached a felled branch and jumped onto it, but whilst mid air the baby fell to the ground. Along came a male - I am reluctant to assign biological fatherhood, because Rhesus Monkeys practice Multiple Paternity, a society whereby multiple males can take part in infant caregiving, for a variety of reasons including uncertainty in who the biological father is; to impress the mother for future mating opportunities; and as social bonding with other males. - After frustratedly pushing the baby onto the log, he jumped ahead and laid his arm out straight, as a ramp, for the infant to gleefully trot up, onto his back. They then continued onwards into woods.

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Elsewhere I saw adolescents free diving from branches overlooking a small river. They would swim back to shore then have another go. Perhaps these were repeated attempts to forage in the water, however the lack of success they were having made this activity seem distinctly like play! Their ability to communicate the arrival of food (in Kowloon, usually a large pile of bread illegally dumped by a passing car) to friends many kilometres away, with loud whoops which spread outwards in a chain reaction, is astounding.

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It is not unusual for a species to go through a hard time at the hands of humans. Ecological domination is the thing we do best! The Rhesus Macaque is unique amongst primates in that it is, in part, due to their success as a species, but also due to interventions from humanity, that they are in a position where they simultaneously thrive and face abuse. Above all, this composes a complex and interlaced story of human and monkey. There was hope for the Rhesus Macaque in 1978, when India introduced an export ban. This was not especially effective, and in 2022 specific protection for the species was removed from their ‘Wildlife Protection Act’. This resulted in a rise in cruel capture and export. A ‘US National Academies of Sciences, Engineering and Medicine’ report, in 2023, actually reported a major shortfall in the global supply of the species due to increased demand in medical research. This could mean a dire fate for many monkeys as they are sourced from countries with lacklustre regulations, for example India as of 2022.

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Arguments have been given that it is somewhat thanks to humans that they have seen such success (Eve B Cooper et al., 2022). I am of the belief, however, that humans have an almost entirely negative impact on these primates. They have proven themselves to be able to adapt to some of the world's harshest environments. Despite often thriving near human habitat, this is purely out of convenience rather than necessity. If those humans, and their ecological destruction, disappeared, the Macaques would rapidly readjust. Despite what we put them through, I would not be surprised if the highly resourceful Rhesus Macaque outlasts even us. As mankind trudges ever closer to societal breakdown, ruthless competition over resources, and inevitable catastrophe, the Rhesus Macaque will merely move further up the mountain, deeper into the forest, where it will regroup, adapt, and flourish.

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