Monkey facts

• The largest species of monkey is the mandrill (Mandrillus sphinx).
• The smallest species, the pygmy marmoset (Cebuella pygmaea), weighs about the same as an orange.
• Monkeys are intelligent communicators and can tell each other secrets.
• Some macaques pickpocket tourists to bribe them for food.
• Most monkeys have opposable thumbs, which help them to grip, groom and manipulate food. 
• Great apes are not monkeys but are closely related.

With a reputation for being cheeky and playful, monkeys have entertained humans for centuries. But their fast reactions and smart thinking didn’t evolve for our amusement – they are adaptations to living in complex societies in the treetops. Monkeys are a diverse group of mammals that usually live in large, social groups and display complex and interesting behaviours.¹ These help them to form social bonds, care for offspring and work together to problem-solve.

Monkeys have stereoscopic vision, which means that they have two forward-facing eyes that allow them to judge distances and three-dimensional shapes more easily – essential for a life spent jumping from branch to branch.²

They can use their intelligence and fast reactions to do some remarkable things. Macaques in Southeast Asia have learned to steal phones, sunglasses and bags from tourists and hold them to ransom – only returning the belongings when they feel the tourist has suitably paid in food.³

Monkeys are as physically diverse as they are intelligent. The smallest monkey is a pygmy marmoset (Cebuella pygmaea), which weighs in at around 100g – around the same as an orange.⁴ This tiny grey-furred species might almost look like a squirrel from a distance as it dashes across a branch. It has an unusual feeding habit too – it gnaws holes in gum tree trunks and laps up the sticky secretions.

Mandrills (Mandrillus sphinx), native to Cameroon, Congo, Equatorial Guinea and Gabon in West Africa, are the largest species of monkey.⁵ They are a colourful and characterful species, immediately recognisable for their bright blue and red faces. The males' faces tend to be larger and brighter coloured – the vividness of the colours making them more attractive to females and warning their male rivals of their dominance. Male mandrills also have brightly coloured bottoms, with the blue and pink skin visible beneath their thin fur being another show of dominance.

Monkeys have extraordinary dexterity in their fingers. They have very strong grips, which make them skilled climbers. But they can also manipulate objects to find food, and even use tools.

Their slender and strong fingers and thumbs are perfect for picking apart fiddly seeds and fruits. Most apes and monkeys also possess opposable thumbs – meaning, unlike most mammals, their thumbs are rotated to face their fingers.⁶

With their long tails, grasping hands and cheeky expressions, monkeys are some of the most familiar animals in the world. However, not everything that looks like a monkey is a monkey.

You see, “monkey” is not a very scientific term, and actually refers to most members of a group of mammals called simiiformes. Simiiformes range from tiny pygmy marmosets to giant lowland gorillas. But not every simiiform is a monkey. A subset of large simiiformes that lack tails and come from Africa or Southeast Asia are called apes and not monkeys.

Apes can be split again into two groups: great apes and lesser apes. The most recognisable great apes are chimpanzees, gorillas, orangutans and humans, while lesser apes are also known as gibbons. So, these animals are apes, and not monkeys, but everything else in the simiiform group can be called a monkey.

Humans aside, the great apes are the largest primates, and can reach sizes of 176cm (5ft 9 inches) tall and 138kg.⁷ Great apes also live slightly longer on average than their monkey cousins. The longest-living monkeys in captivity are capuchins  – a white-faced, black-bodied species from Central and South America – but great apes such as gorillas, chimps and orangutans can live slightly longer in the wild.⁸ The longest verified lifespan of a wild great ape is 58 years for an orangutan. The human has the longest lifespan of all great apes and has a lifespan of around 80 years. 

You might also hear the word “primate” used for monkeys and apes. Primate is the scientific name for the order that all monkeys and apes belong to. Primates also include animals like lemurs, bush babies and slow lorises – the latter two are often nocturnal and mostly tree-dwelling, fruit-eating and wide-eyed creatures. 

All primates evolved for life in treetop communities, developing features like long arms for swinging from branches, good vision for spotting food among foliage, and large brains to help form social bonds. However, some primates like gorillas, baboons and humans are now adapted for life back on firm ground.

Of all the living primates, only the human walks upright on two feet for any length of time, but some lemurs and monkeys can skip on two feet for short distances when they need to quickly run along the ground between trees.

Humans are one of the great apes, closely related to chimpanzees and bonobos. We share a common ancestor with our chimpanzee cousins that evolved around 6.5-7.5 million years ago. In evolutionary terms, this is not a very long time, so we have much in common with chimpanzees genetically. While it was once thought that humans and chimps share 99% of their DNA,  recent studies suggest this number may be slightly lower.⁹

Apes and monkeys are very closely related and both belong to the primate order. The first primate evolved around 60 million years ago, during a time of significant climatic and ecological change after the extinction of the dinosaurs. These first primates were small mammals with four short legs, a tail and a rodent-like head. Over time, they evolved to be better suited to life in the trees – with opposable thumbs, stereoscopic eyes and long tails.

We have many things in common with our monkey cousins – furless faces that make communicating with facial expressions easier, grasping hands ideal for holding onto branches or tools, and teeth and digestive systems that are suited to a diet that includes both meat and plants.

Humans and monkeys usually have only one or two offspring at a time and invest a great deal in raising their infants. Almost all primates today live in close social groups, but ancient primates were likely solitary or lived in loosely associated groups. As primate brains grew, they evolved social skills that had big benefits for childcare. With extended family nearby to help find food, nurse, groom and defend against rivals, primates had a much higher rate of success.

While great apes have been the subject of extensive language research, less scientific attention has been paid to monkeys.¹⁰ But monkeys are also intelligent and complex animals that are highly capable communicators. Monkeys need language to maintain their social structures. From alarm calls to soothing and grooming, using language helps monkeys to bond and keep each other safe.

Monkeys, like marmosets, take turns to speak, indicating they change their meaning based on the responses of their conversation partner.¹¹ They're also able to understand when a conversation is being held and secretly out of earshot of other monkeys.¹² 

Apes, with their larger brains and complex social dynamics, might be better placed to learn a new language. They have high-profile examples of captive apes learning human-like language.¹³

Some chimpanzees appear to learn sign language to communicate with their keepers. One famous example is a chimp called Nim Chimpsky (a pun on the name of the famous linguist Noam Chomsky). Nim learned several pieces of vocabulary from the American Sign Language lexicon, including nouns like “apple” and “banana”, verbs like “give”, “tickle” and “hug” and his own name.¹⁴

However, it is disputed whether Nim really understood the meaning of these signs, as he might have been randomly copying the hand signals of trainers until he received a reward. Nim’s messages lacked structure. For example, he signed messages like “Eat me Nim drink”. The longest series of connected signs he made was "Give orange me give eat orange me eat orange give me eat orange give me you." So, Nim was some way off forming a complete sentence.¹⁵

Featured image © Utkarsh Singh | Unsplash

Fun fact image © | Edwin Butter | Shutterstock

1. Welker, C. “[the Social Structure of Primates].” Anthropologischer Anzeiger; Bericht Uber Die Biologisch-Anthropologische Literatur, vol. 43, no. 2, 1 June 1985, pp. 97–164, pubmed.ncbi.nlm.nih.gov/3927823/#:~:text=The%20social%20units%20of%20most. Accessed 9 June 2024.

2. “Mammals of Africa.” Google Books, 2015, books.google.co.uk/books?id=B_07noCPc4kC&pg=RA1-PA45&redir_esc=y#v=onepage&q&f=false. Accessed 19 Sept. 2024.

3. “BBC One - Planet Earth III, Series 1, Human, Sir David Attenborough and the Stealing Macaques.” BBC, 29 Nov. 2023, www.bbc.co.uk/programmes/p0gwn003. Accessed 19 Sept. 2024.

4. Converse, Lisa J., et al. “Communication of Ovulatory State to Mates by Female Pygmy Marmosets, Cebuella Pygmaea.” Animal Behaviour, vol. 49, no. 3, Mar. 1995, pp. 615–621, https://doi.org/10.1016/0003-3472(95)80194-4. Accessed 3 Feb. 2020.

5. “The Kingdon Field Guide to African Mammals.” Google Books, 2015, books.google.co.uk/books?hl=en&lr=&id=p1hMCAAAQBAJ&oi=fnd&pg=PA1&dq=Kingdon. Accessed 19 Sept. 2024.

6. “Mammals of Africa.” Google Books, 2015, books.google.co.uk/books?id=B_07noCPc4kC&pg=RA1-PA45&redir_esc=y#v=onepage&q&f=false.

7. Finch, Caleb E., and Steven N. Austad. “Primate Aging in the Mammalian Scheme: The Puzzle of Extreme Variation in Brain Aging.” AGE, vol. 34, no. 5, 5 Jan. 2012, pp. 1075–1091, www.ncbi.nlm.nih.gov/pmc/articles/PMC3448989/, https://doi.org/10.1007/s11357-011-9355-9.

8.  “The Derived Features of Human Life History.” Core.ac.uk, core.ac.uk/reader/276278010.

9. Suntsova, Maria V., and Anton A. Buzdin. “Differences between Human and Chimpanzee Genomes and Their Implications in Gene Expression, Protein Functions and Biochemical Properties of the Two Species.” BMC Genomics, vol. 21, no. S7, Sept. 2020, bmcgenomics.biomedcentral.com/articles/10.1186/s12864-020-06962-8, https://doi.org/10.1186/s12864-020-06962-8.

10. Meunier, Hélène. “Do Monkeys Have a Theory of Mind? How to Answer the Question?” Neuroscience & Biobehavioral Reviews, vol. 82, Nov. 2017, pp. 110–123, https://doi.org/10.1016/j.neubiorev.2016.11.007.

11. Takahashi, Daniel Y., et al. “Coupled Oscillator Dynamics of Vocal Turn-Taking in Monkeys.” Current Biology, vol. 23, no. 21, Nov. 2013, pp. 2162–2168, https://doi.org/10.1016/j.cub.2013.09.005.

12. Brügger, Rahel K, et al. “Do Marmosets Understand Others’ Conversations? A Thermography Approach.” Science Advances, vol. 7, no. 6, 5 Feb. 2021, https://doi.org/10.1126/sciadv.abc8790.

13. Arbib, Michael A. “From Monkey-like Action Recognition to Human Language: An Evolutionary Framework for Neurolinguistics.” Behavioral and Brain Sciences, vol. 28, no. 2, Apr. 2005, pp. 105–124, https://doi.org/10.1017/s0140525x05000038.

14. Snowdon, Charles T. “Learning from Monkey “Talk.”” Science, vol. 355, no. 6330, 17 Mar. 2017, pp. 1120–1122, https://doi.org/10.1126/science.aam7443.

15. Terrace, H. S. How Nim Chimpsky Changed My Mind. Google Books, Ziff-Davis Publishing Company, 1979, books.google.co.uk/books/about/How_Nim_Chimpsky_Changed_My_Mind.html?id=E2v7SAAACAAJ&redir_esc=y. Accessed 4 Nov. 2022.