Never a subterranean termite like Reticulitermes grassei will build the termite mound of a species that nests in wood, like Kalotermes flavicollis. Neither will a stork build a pigeon’s nest nor will a bee make a wasp’s honeycomb. A zebra does not have to be taught to flee from a lioness, nor a wildebeest from a crocodile.
They are behaviors that are not learned and are part of the innate repertoire of each species. They are controlled by genes and are therefore inherited. They arise automatically when the specific stimulus appears, and all individuals of the species respond in a practically identical way.
Signs that seduce (and who)
The anatomical, physiological and behavioral differences between the two sexes attract the opposite sex. Female peacocks “fall in love” with a peacock’s fan of feathers, but chickens are insensitive to it. Up to 14,000 different songs have been described in birds: each species has its own “musical language”. For females, the song of a male of their species is an aphrodisiac and that of a male of another is irrelevant.
A lion’s mane attracts lionesses, but not tigresses. Furthermore, it has been described that the length of said coat is related to success in competition with other males and to the reproductive life expectancy of the specimen that carries it. It has also been seen that their offspring have a higher survival rate.
The silver back of a gorilla emerges after a notable release of testosterone, indicates sexual maturity and leadership, and is irresistible to female gorillas, but not to female chimpanzees.
The silver back of gorillas is related to the release of testosterone. Wikimedia Commons., CC BY
The organs that emit signals in males co-evolve with the receptor organs that females of that species have in unison: they emit signals, they develop senses that interpret them and react accordingly to those signals. If the concerted evolution of the two sexes goes out of rhythm, the species ends up becoming extinct, something that has happened countless times throughout evolution.
It is also the case that sometimes these systems are not perfect. A lion can roar loudly, sport a magnificent mane and successfully defend its territory, but have reduced fertility due to a low sperm count or even sterility if it does not have spermatogenesis. Appearance does not always correlate exactly with reproductive health.
Remote controlled pheromones
Along with visual and sound stimuli, there is another chemical language: pheromones. Sexual pheromones are molecules that are released into the environment by one of the sexes and that are not seen, but are detected by the opposite sex and function as seductresses.
They are also species-specific, thus reinforcing reproductive isolation: they prevent females of one species from responding to the pheromones emitted by males of another, which would involve a useless expenditure of energy since, if it occurred, copulation would not be productive. They are widely distributed in the animal kingdom, which shows a very ancient evolutionary origin.
We humans
Our species cannot completely escape its own biology: we constantly emit and decode signals. For example, secretions from the mother’s areolar glands stimulate the sucking reflex in human newborns. It has been shown that babies respond to their smell even before they have been previously fed. They induce responses such as head orientation and oral movements in the baby, facilitating the location of the nipple and the natural sucking reflex.
On the other hand, androstadienone, a potential human pheromone derived from testosterone found in sweat, semen and other male body fluids, appears to be involved in sexual attractiveness, although its effect depends on the context.
As in other species, we respond to these signals, although in us an extraordinary complexity is added: that provided by culture, that second nature that we possess.
Time does not pass in vain
In the same way that an aging lion loses part of its mane and is less attractive to the opposite sex, in humans there are signs that show the loss of reproductive vigor. An obvious example is facial symmetry, which is usually associated with beauty and health. With age, the face reflects the passage of time and that perception of attractiveness tends to decrease. The loss of skin smoothness and muscle sagging also contribute to this.
Somehow aging sends signals that our reproductive potential is declining. Added to all this are other factors: expression, voice, the resources that each individual possesses or the health they project.
Catherine Hakim, in her book Erotic capital: the power to fascinate othersanalyzes how these aspects influence the perception of attractiveness. In humans, courtship and mate choice combine instincts, pheromones and culture in a complex and variable mixture depending on the social context.
The fascinating thing is to think that behind each person we are attracted to there are millions of years of evolution and centuries of shared culture, organized in the deepest part of our being.
This article was originally published on The Conversation.