In the course of our evolution, singing behavior has played a very important role in our survival and that of animals, especially birds, singing animals par excellence. The primary function of this activity is fundamentally linked to reproductive activities, the search for food and above all to avoid dangerous predators. In our ancestors, this became fundamental as we began to lead an increasingly terrestrial and less arboreal life. This change has led to increased development of our intellectual and cognitive abilities, allowing us to build rudimentary defensive weapons like claves, spears, etc., to defend ourselves against predators, especially large cats such as lions and cheetahs.
It was observed going from the simplest animals to our closest relatives, chimpanzees, that these cousins of ours, when they had to defend themselves against attacks from big cats, along with the use of sticks and throwing stones, issued very loud squeals and vocalizations. They never defended themselves in silence. Our ancestors and chimpanzees, during these activities, kept themselves as much as possible in an upright position to better identify the enemy, especially in high vegetation, for example, in the savanna. In essence, at the beginning of humanity, those who really dominated the savanna were the big cats and our ancestors, who hunted and fed on carcasses of prey partly eaten and then abandoned on the ground by the felines.
In addition, the cries issued by our ancestors, more than an emotional response in the face of a dangerous situation, were issued to intimidate the enemy and send him away. The cries served to attract the attention of neighbouring human groups and to involve them in common defense; in essence it was no more than the search for solidarity.
As far as solidarity is concerned, it is no coincidence that children, before they start speaking, issue very loud cries to attract maternal attention and a need for care and reassurance. Often children who squeal in the crib do not need anything special but to feel close to the maternal figure.
Frequency and intensity of sounds
The relationship between the frequency and the minimum intensity necessary for a sound to be heard by man takes the form of an inverted bell curve in which the tones between 30 and 130 decibels (dB), with frequencies between 1500 and 3000 Hertz (Hz), are those we can hear without problems, at least for a short time for the highest tones. The ability to process information in man, and only in humans, has allowed us to make an exceptional evolutionary leap. It has allowed the fundamental development of the articulated language and then of music. But how has the selective sound capacity evolved throughout our history?
In order to answer we must start from when we were not Homo sapiens yet, that is, from our very distant ancestors when they began to descend from trees to lead an increasingly terrestrial life. The change in arboreal life (from a vertical dimension of the world) to the earth (to a horizontal dimension of the world) has taken on a fundamental role in the information content of sound emissions, when men still did not dominate the world and more than predators they were prey. Everything, however, has had to do with the evolution of the brain that has become bigger in humans, compared to the weight of the body and that of all other animals. To put it mildly, an elephant could never have climbed the branches of a tree, too heavy to do so and with a relatively small brain, while our non-human next of kin, that is, the monkeys, could have done so very ease and with a strong sense of balance. Prosimians are arboreal animals par excellence, so are all cercopithecides and gibbons, while the gorilla and orangutan who are very heavy apes do it much less.
What is the function of alarm cries? The terrestrial monkeys that use the alarm cry most are mainly baboons, macaques, guenons, colobines, drills and other genus of monkeys. These are alarms that are intended to ward off large cats, predators that, by the way, cannot climb trees so easily so they became a safe refuge for all these monkeys. Then, once the danger is over the monkeys come down to the ground as do domestic cats in order to defend themselves against attacks by dogs. In addition, practically all the South American monkeys scream a lot and spend about 90% of their time in the tops of the trees where they mostly sleep and move. Their food is mainly on trees and therefore it is not necessary for them to come down to find it. In the forest, however, there is little visibility and therefore their call cries are mainly aimed, more than anything else, at keeping groups together which are generally rather small. Do we have to ask ourselves why the terrestrial animal that uses the most calls on the ground is man when we know that they often attract the attention of predators? The fact is that open field cries can be as important as those emitted in the thick of a forest. Our ancestors were able to overcome this problem with the development of a society increasingly supportive and enlarged than that which existed in the forest, a place where monkeys constituted numerically small groups and therefore more vulnerable. In conclusion, the calls to the ground serve more to defend themselves, while in the trees they are to keep the group to which one belongs as united as possible.
In humans, it is evident to everyone that the tone of the male voice is different from the female one. Musically the difference is of an eighth, enough to distinguish and characterize different emotional states or to attract the attention of others in a situation of danger or in moments of suspense and in which sounds are emitted. In these situations, the loud and distinct sounds emitted by women are recognizable even at a long distance. In the face of danger, women make much more acute sounds than men, indeed men in the face of danger generally become mute, women much less. Why do these differences exist, taking into account the anatomical diversity between man and woman? In order to answer this question, we must once again go back to our ancestors where defence was necessary for the survival of the groups. The women were occupied with their young children, more than hunting, harvesting wild vegetables and fruit and therefore were more exposed to the dangers of the savanna. Their loud and acute calls of alarm caught the attention of the men who immediately rushed to their defense and of their offspring. We have still maintained this diversity of sound between man and woman. The emission of alarm sounds, is therefore not a stereotype, but is functional to the maintenance of sociality and solidarity between males and females, that is between genders.
Cheney, D.L. & Seyfarth, R.M. 1990. How monkeys see the world: Inside the mind of another species. Chicago, Chicago University Press.
Tomasello, M. 2008. Origins of human communication. Cambridge, MA., MIT Press.
Jordania, J. 2014.Tigers, Lions and Humans: History of rivalry, conflict reverence and love. Ed. by A. Jordania. Australia, Logos.