Many investigations conducted over 40 years reveal that humans and big apes are distinguishable from other nonhuman primates by their ability to recognize themselves.
Scientists examine some recent advances in the discipline, paying special attention to claims that monkeys exhibit self-recognition.
Chimpanzees recognize their own species
Chimpanzees have been observed interacting with deceased members of their species, revisiting bodies, and even displaying mourning-like behavior, as per Phys.org.
Elephants are known to do the same thing, and will even engage with elephant skeletons.
But do chimps recognize and prefer conspecific bones belonging to their species?
Previously, the scientific community paid little attention to this, maybe presuming that chimps know little or nothing about chimp bone structure.
This type of subject has recently been investigated in the realm of comparative thanatology.
Since the initial demonstration of mirror self-recognition in chimps and the failure of macaques to demonstrate self-recognition, much study has been undertaken on mirror-image reactions in monkeys and apes.
This research leads to the following general conclusion on how nonhuman primates interpret their reflections in mirrors individuals of most great ape species have demonstrated persuasive evidence that they identify themselves, but no monkey has done so.
The apparent separation within the order Primates, on the other hand, continues to provoke criticism and significant disagreement, despite repeated efforts to obtain data that would bridge the gap.
In this section, we analyze recent advancements in the discipline and focus on critical methodological difficulties.
A team led by Andre Goncalves from Kyoto University has recently tested chimps' visual attention to a sequence of photographs of conspecific and non-conspecific skulls.
"We utilized photos of faces, skulls, and skull-shaped stones to symbolize four distinct species," Goncalves explains.
According to the researchers, chimp skulls include face-like clues, basic shapes, and an overall eye-nose-teeth configuration that likely triggers a network of brain areas that evolved to identify and analyze faces.
Put bluntly, chimps appear to distinguish whether a skull resembles a chimp's skull, which is connected to the phenomenon of pareidolia, which is linked to the brain's ability to sense faces.
Read more: Monkeys can Do Math, Study Finds
Response of monkeys to mirrors
A claim of mirror self-recognition in rhesus monkeys was one recent challenge to what is known as the cognitive division theory of self-recognition, as per PLOS.
Individually housed monkeys occasionally moved an acrylic block screwed into their skull for neurophysiological investigations, and some of these manipulations happened as the monkeys stared in a mirror at their reflection.
The same monkeys, however, exhibited no indications of self-recognition in a typical mark test.
Furthermore, no baseline information was provided, and no quantitative data on block alteration were reported while searching elsewhere.
The mark test demands that the mark be applied in such a way that the subject is unaware of its presence until it is seen in a mirror.
One especially remarkable element of how monkeys respond to mirrors is that, although showing no symptoms of self-recognition, they can learn to discover otherwise concealed items through mirrored signals.
In one research, macaques that saw their reflection in the mirror of an item dangling above them lunged for it. It is hardly strange, then, that things affixed to a monkey's head would draw exploration.
To see if implanted rhesus monkeys know themselves, remove the implants and allow the incision to heal completely.
The monkeys will next be subjected to a standard mark test. If they fail, any claim that the monkeys had learned to recognize themselves would be ruled out.
Related article: Monkeys Can Decide When to Speak Up or Stay Silent, Researchers Say