Studies made on monkeys revealed they have a so called "self consciousness" and are gifted with high learning ability.

In monkey groups there is a strict hierarchy and the orders of the superior individuals are executed by the whole group. Monkeys are able to communicate their intentions, decisions, satisfactions and dissatisfactions. When the offspring disobey their parents, they are punished.

Many monkeys and all apes pass the mirror -recognition test for self-awareness. Monkeys have visual and auditory abilities very similar to those of humans. The facial expressions and some hand gestures of the monkeys and apes are easily understandable for humans.

Monkeys and apes communicate primarily through vocal means, but the precise meanings of their vocalizations are not currently known. Scientists supposed for long time that the sound emitted by monkeys are actually symbols representing objects, places, intentions, food, being made by short series of consonants and vocals, like the human onomatopoeias.

The "monkey" language can vary from one group to another, and is composed of guttural sounds and gestures known by the whole group. As these are learned, not transmitted genetically, they depict a speech culture (chimps, gorillas and orangutans are also known for their tool culture). The Vervet monkeys, from South Africa, use three different alarm calls, each corresponding to a different predator type. The call for snake makes them jump back and examine the grass.

When the call announces an eagle, the monkeys hide in the bush and if the call is for leopard, they dash to the top of the trees. Monkeys were proven to be able to count to four and to be aware of the difference between human languages, let's say Japanese and Dutch. Through different approaches, researchers have tried to make at least 20 monkey species communicate with us employing typical human methods.

The abilities of the big apes did impress indeed the scientists. For a long time, researchers regarded chimps as much more intelligent than gorillas and orangutans, as they are more genetically related to us, but this is a misconcept. Gorillas and orangutans are slower and possess life styles more different than ours, being harder to motivate than chimps.

In apes, brain frontal lobe is, like in humans, the site of their intelligence. They just lack an articulated language, due to their laryngeal structure, and a lower capacity to abstract. And like humans, different individuals are more or less intelligent.

Trained lab chimps and bonobos have managed to learn over 400 object symbols, and even operate with them. They can type using a special keyboard of lexigrams (geometric symbols), and can respond to spoken sentences. They can press the keys to express needs, wishes or just communicate something to their trainer.

Trained orangutans, gorillas and chimps can learn human signal languages like the American one: from several hundreds for orangutans to over 1,000 for gorillas and 800 for chimps.

Their rhythm of learning is 40 new words per year.

Do not think that apes learn the sign languages like a simple circus training: they arrive to effectively think, associate notions, ask, generalize, negate, regret, envy, try to teach others, express their feelings (including disappointment), plan and so on.

And what's more, these apes and others grown in a human environment can understand human spoken language (like English). One bonobo understood over 3,000 spoken words in English and gorillas about 2,000. The same bonobo can play simple video games.

Gorillas show a certain preference in their words combination (8-10 words). When they do not know a new object, they characterize it by color, shape or function. For example, for a swan "bird-water", an orange "fruit-scent", a poignant radish "food-pain".

Moreover, if we were to bring a proof that monkeys do lie, trained gorillas do lie (chimps too) (an evidence of a sense of self), blaming by signs others when they are guilty and they even swear by signs, using the words "dirty", "ugly", "stupid" and "closet". Apes also laugh, so they indeed have self awareness.

Based on these types of observations, researchers compare the intelligence of adult apes with that of a 6 year-old child and attribute them personhood. When a trained chimp was asked to assign pictures in two categories, animals and monkeys, the ape included without hesitation human images amongst monkeys.

Above: Kanzi, a bonobo that use lexigrams

Below: Koko, a gorilla that uses the sign language