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Studies on great apes have revealed that these extraordinary creatures, our closest relatives, often display behaviors that are strikingly human. While the media tends to exaggerate their language abilities, research shows that these animals have demonstrated an impressive grasp of the fundamentals of language. The growing body of research also highlights the social parallels between us and great apes, with new revelations emerging regularly.
But what about monkeys, our more distant relatives? As we trace the evolutionary path back to these less-developed cousins, it might seem like they share fewer common traits with us. While this is partly true, recent findings have uncovered that monkeys are far more like us than we ever thought.
10. Monkeys Can Learn to Recognize Themselves in Mirrors
Humans and great apes have the unique ability to recognize themselves in mirrors, a skill that only a few other animal species possess. Traditionally, it was believed that monkeys were incapable of this form of self-awareness.
However, this perception began to change in 2015 when researchers from the Chinese Academy of Sciences discovered that rhesus monkeys, despite initially failing to recognize themselves, could be taught to do so. They introduced training methods that included a variation of the standard mirror self-recognition test, which involves marking a monkey’s face and checking if it can identify the mark in the mirror.
The researchers placed the monkeys in front of a mirror and directed a laser beam at them. The monkeys received a food reward whenever they touched the laser spot on their own faces, as seen in the mirror. After two to five weeks of training, the monkeys began to regularly perform this task.
The findings were published in the journal Cell Biology. The study indicates that, even after the experiment concluded, many monkeys continued to engage in mirror-induced behavior independently. The researchers suggest that while monkeys may lack the neurological “software” for self-recognition, they possess the necessary “hardware” within them to accomplish it.
This distinction between innate self-recognition and an underdeveloped yet present ability to recognize oneself can offer valuable insights into the evolution of neural mechanisms for mirror self-awareness (and consciousness in general) in primates, including humans.
9. Monkeys and Humans Share Similar Face-Recognition Abilities
We retain a tremendous amount of information about people, both consciously and unconsciously, particularly when it comes to those we are closely related to, such as family members or even acquaintances like fellow churchgoers.
In a 2010 study at the Max Planck Institute for Biological Cybernetics in Tubingen, Germany, researchers found that both humans and monkeys rely on similar biological processes to interpret facial information. They used the well-known “Thatcher illusion” to support their findings.
The Thatcher illusion reveals that the brain struggles to process a face when it is upside down. What may appear to be a normal image is actually distorted before being flipped and shown, making it hard for the brain to recognize the distortion.
The German researchers, who published their findings in Proceedings B of the Royal Society, had both humans and macaque monkeys examine two images of a face side by side—one in its normal form and the other distorted. Two additional sets of these same images were shown upside down. The same setup was later presented using faces from the opposite species.
For the humans observing their own faces, it was easy to identify the distorted photo when oriented correctly, but the upside-down images triggered the Thatcher illusion, as expected. However, when viewing macaque faces, the Thatcher illusion appeared with all the photos, making the distortions almost imperceptible.
The monkeys were first accustomed to the environment and then fitted with a headpiece to track their eye movements. The results showed that the monkeys behaved similarly to the humans, easily identifying distortions in their own species' faces (but only when the faces were right-side-up), but not in the human faces.
Both humans and monkeys perceive faces holistically. If the Thatcher illusion is confirmed in both species, it would suggest that their brains have evolved in comparable ways to process facial features.
8. Monkeys May Have Memory Abilities Similar to Ours
When you remember a childhood moment after seeing a photograph, that's called 'recognition.' On the other hand, being able to recall and describe that memory without an image to trigger it is called 'recall,' which is a more complex mental process. A 2011 study published in Current Biology revealed that, like humans, monkeys have the ability for both types of memory, and their memory functions more similarly to ours than previously believed.
The study, led by Benjamin M. Basile and Robert R. Hampton, involved training rhesus monkeys to identify and replicate simple shapes on a touchscreen computer. The researchers concluded that recall in both humans and primates could have been an adaptive trait shared by a common ancestor before human and rhesus lineages diverged, with monkey recall mirroring that of humans.
To distinguish between recognition and recall, the researchers developed a test for monkeys that involved five rhesus monkeys. They were shown three boxes on a grid and, after a brief delay, were asked to 'draw' the remaining boxes by touching the correct spots on the grid. As with humans, the monkeys found it harder to remember shapes in recall tests compared to recognition tests. Once the recall ability was established, it deteriorated more slowly over time than recognition. The monkeys also demonstrated the ability to recall novel shapes that they had not been specifically trained with.
7. Monkeys May Have Levels of Peripheral Perception Similar to Ours
Humans often have the ability to perceive and respond to stimuli before our conscious minds process them. This peripheral vision helps us navigate our environment and avoid potential threats without being fully aware of them.
A study involving five rhesus monkeys, published in 2013 in the journal Animal Cognition, suggests that monkeys also possess this ability for peripheral perception.
The monkeys were trained to use a touchscreen to select one of four briefly shown locations. In a second test, they indicated whether an object was present or absent by pressing one of two buttons. The researchers used 'visual masking' to control how easily the visible target could be processed.
As expected, accuracy declined when visual masking was applied. However, even with the target masked, the monkeys were still able to locate it, even though they were unaware of perceiving it. This test, which is also used in humans, yielded identical results. This finding provides evidence that the dissociation between conscious and unconscious (peripheral) vision in monkeys mirrors that in humans.
Dr. Lau Andersen, the lead author of the study, stated, 'Understanding whether similar independent brain systems exist in humans and nonverbal species is essential for advancing our knowledge of comparative psychology and the evolution of brains.'
6. Monkeys Might Make 'Irrational' Decisions Just Like We Do
Humans often make value-based decisions by approximating the overall worth of various objects in front of us. This can be a useful skill, but it sometimes leads to poor choices. For example, would you prefer a delicious piece of fruit or a tasty fruit along with a bland carrot? Many would choose just the fruit, even though the addition of the carrot should logically make the second option better. This happens because our brains tend to simplify decision-making processes, which can lead to irrational decisions.
To explore why this happens and whether monkeys share this tendency, Jerald D. Kralik and his team conducted a study, published in PLOS One in 2012.
The researchers found that rhesus monkeys, similar to humans, preferred high-value food over the same food paired with a positive but lower-value food. Under certain conditions, these preferences evolved into an 'affect heuristic,' leading the monkeys to make irrational decisions by choosing less food. The study suggests, 'The persistence of this affect heuristic could explain similar irrational biases in humans, reflecting a broader strategy for simplifying decisions, where averages, prototypes, or stereotypes represent a group or set.'
5. Monkeys and Humans Can Make Similar Decisions in Other Ways
In 2014, researchers from New York University and Stanford University made significant strides in understanding the processes behind decision-making and how both humans and monkeys change their minds. By recording the activity of multiple neurons at once, rather than analyzing individual neurons, they were able to capture the complexities and dynamics of decision-making without the distortion of previous methods.
In a study published in Current Biology, lead author Roozbeh Kiani and his team worked with macaque monkeys, putting them through a series of tests while monitoring their neural activity. The tests involved showing the monkeys patches of randomly moving dots on a screen. After sending a 'go' signal, the monkeys would report the direction of the patches by moving their eyes. The researchers aimed to predict the monkeys' movements based only on the neural activity just before the 'go' signal.
The researchers used their model to examine the dynamics of the monkeys' decision-making at various moments before the 'go' signal. They found that decision-making was often unstable, with the monkeys shifting their choices back and forth. This process of changing decisions mirrored the way humans handle similar neurological tasks involving decision-making, as demonstrated in a 2009 study.
4. Monkeys Share Many of Our Economic Biases
Do monkeys tolerate price gouging like humans do with brand-name products? According to Laurie Santos, a psychologist at Yale University, and Yale undergraduate Rhia Catapano, they do not. These two researchers co-authored a December 2014 study examining the economic behavior of monkeys.
It is well-established that social primates have some understanding of markets and even exhibit similar economic biases to humans. For example, previous research by the authors has shown that monkeys are loss-averse, exhibit irrational behavior when faced with risk, and tend to rationalize decisions, much like people do.
However, there is one area where our primate relatives differ: they aren't swayed by brand names or similar marketing tactics. It's well known that many humans are inclined to purchase a more expensive item over a less expensive one, even if both are essentially the same. The pricing of wine is a classic example of this behavior.
To explore the origins of this behavior, the researchers and their team worked with a group of brown capuchin monkeys trained to use a token system to buy food. They wanted to test whether the monkeys would use price as a signal of value. While the monkeys understood the prices of various goods and demonstrated the ability to switch to cheaper options when prices increased, the study revealed that the monkeys were not deceived by manipulated prices.
It might seem like humans are easily duped by price tags, but this actually highlights our more complex understanding of market dynamics. We associate high prices with items that are popular among our peers, even if they mislead us. In contrast, monkeys lack this social context when it comes to markets.
3. Monkey ‘Language’ Is More Sophisticated Than Previously Thought
Recent studies are revealing that monkeys use language in ways that are far more intricate than previously believed, with some monkeys from the same species displaying different 'dialects' depending on their geographical region, much like humans do.
Philippe Schlenker, Senior Researcher at the Institut Jean-Nicod within the National Center for Scientific Research (CNRS) in France and a Global Distinguished Professor at New York University, explains, 'Our findings reveal that Campbell’s monkeys differentiate between roots and suffixes, and their combination enables the monkeys to describe both the nature of a threat and its level of danger.'
A 2014 study by a team of linguists and primatologists examined the alarm calls of Campbell’s monkeys and found that these monkeys have two primary words: 'krak' for leopard and 'hok' for eagle. Additionally, they use a series of modulating sounds, such as '-oo' (which generalizes danger or signifies that the threat is invisible) and 'boom boom,' which means the call is not related to predation and can mean 'come here' or 'over here.' The researchers discovered six distinct calls in total, which can be combined to express different meanings. For example, 'boom boom krak-oo krak-oo krak-oo' means 'watch out for falling trees,' while 'hok hok hok!' is used to warn about an eagle.
The first breakthrough in decoding monkey vocalizations came with velvet monkeys, who were found to have three distinct calls for predators, though there was no evidence that they were capable of manipulating the meaning of their calls.
The researchers studied two groups of monkeys from the Tai forest and Tiwai island, discovering that their calls had different or altered meanings based on the region. The authors suggest that this variation is due to a form of linguistic 'competition,' which is similar to a well-known human phenomenon called 'implicatures,' where a word's meaning can change when it competes with a more informative alternative.
2. Similar Brain Regions in Humans and Monkeys Once Thought to be Unique
The January 2014 issue of the journal Neuron published a groundbreaking article revealing that the brain structures of humans and monkeys are far more alike than previously believed.
The study specifically focused on the ventrolateral frontal cortex, a region responsible for complex functions such as language and higher-level thinking in both species. While some researchers had previously suggested that humans developed an entirely new set of neural mechanisms for such tasks, others argued that evolutionary precursors could be traced back to lower primates.
Franz-Xaver Neubert, the lead author, and his team used MRI scans to compare the brain structures of 25 humans and 25 macaque monkeys. The researchers discovered significant differences between the two species but were also surprised to find many similarities, including 11 components of the ventrolateral frontal cortex that interacted in comparable ways, with similar distributions of brain circuits.
The differences between species might explain why monkeys perform less effectively (or in a different manner) on auditory tasks and struggle with areas such as strategic planning, multitasking, and decision-making. Meanwhile, the similarities could suggest that many of the neural functions in humans evolved from shared, evolutionarily conserved brain structures, and that subsequent modifications to these connections led to the development of distinct functions.
1. Oxytocin's Role in Social Skills and Bonding
Oxytocin, a hormone produced in the human pituitary gland, plays a crucial role starting from birth, including in labor and milk production. It has been shown to influence parental bonding, social interactions, and even mating behaviors. Due to its importance in social development, it has long been studied for its potential medicinal uses. Until recently, it was thought that oxytocin did not have the same function in lower primates.
However, a study conducted by researchers from the National Institutes of Health, the University of Parma in Italy, and the University of Massachusetts Amherst is beginning to challenge this assumption. Their findings, published in the 2014 issue of the *Proceedings of the National Academy of Sciences of the United States of America*, show that oxytocin does indeed enhance social behavior in newborn macaque monkeys.
Researchers administered inhaled oxytocin to infant monkeys and observed an increase in positive social behaviors, such as more communicative gestures with their mothers and heightened social interest. If these results are confirmed, this research could demonstrate that oxytocin has the potential to serve as a powerful early intervention for human children at risk for social and developmental disorders.
