Mutual Aid. Pablo Servigne

designed to highlight this, and, of course, this is what they ended up observing. The history of observing the opposite forces (mutually beneficial relationships) has been much slower work. It really only took off in the 1970s. Today, studies number in the thousands, and it would be very daring, even crazy, to synthesize them all. However, here is a small overview.

       Among one’s peers

      It’s not surprising that ants and bees collaborate in a single colony (the same family). We can also easily observe migratory birds, such as pigeons or arctic terns, flying together (the same species) so as to have a better chance of escaping predators.⁴ Anyone who has ventured to walk across a colony of arctic terns is not likely to forget the ensuing series of furious dives, their sharp beaks lunging forward, punctuated by particularly explicit cries intended to scare away the intruder, most often a marauding cat or fox.

      Associating in order to achieve the same goal is also common among lionesses, who need to hold onto the prey they have caught and prevent hyenas from pilfering it,⁵ and it is even seen on Antarctic ice floes when emperor penguins, while nesting, have to fight against a common enemy: the wind. These large birds huddle together to keep warm, and take turns to occupy the most uncomfortable position: on the edge of the group, facing the blizzard. This is undoubtedly a profitable strategy, because it allows them to withstand perceived temperatures that plunge as low as minus 200°C!

      In starlings, the mating season is dominated by competition, as in most species. But, after singing in early spring, and until the chicks are freed so they can defend the territory necessary to meet the needs of the whole family, starlings gather in groups of thousands of individuals, which gives them a greater efficiency in foraging and makes predator attacks almost impossible.

Trees are not to be outdone. Many species connect their root networks.⁶ In the tropics, for example, trees of the genus Cecropia are pioneers: they are the first to colonize cleared, arid lands. To accomplish this arduous and thankless task, young shoots connect up in a network through their roots, thus pooling water and nutrients. This makes it possible to reuse the root network of those that die first.

       Between distant cousins

      The discovery of the bonds of solidarity between different species is also very old. Witness Herodotus’s famous story of the Egyptian plover (a bird) and the crocodile: ‘[T]he trochilus […] enters into his [the crocodile’s] mouth and swallows down the leeches, and he being benefited is pleased and does no harm to the trochilus.’⁷ During the first half of the twentieth century, discoveries of beneficial interactions between species became more common and quite popular, but curiously enough these were not mentioned in academic texts.⁸ It was not until the 1970s that science accepted the universality of mutual aid between two or several species that lie far apart on the genealogical tree of living creatures. For example, in coral reefs, the clownfish is known to have very close relationships with sea anemones, which use their venom to protect it from predators, in return for the food the clownfish brings them (it is itself immune to the venom).

In the frozen waters of the Antarctic Ocean, another species of sea anemone spends its life on the back of a snail (protection in exchange for transport) in what is akin to obligatory mutualism (a ‘symbiosis’), since neither species has ever been observed without its partner.⁹ Through the protection offered to it by the anemone, the snail has even allowed itself the luxury of saving energy by making a particularly fine shell. We see in this example the extent to which close relationships of mutual aid can become fusional, to the point where the organisms involved are transformed. If you dare to let yourself be transformed in contact with the other creature so that you can both stay alive, you have truly learned how to let go.

      In warmer seas, some small cleaner fish escort large fish, turtles and marine mammals to rid them of their parasites. Following an elaborate dance, the cleaner fish even risk entering the mouths and gills of their hosts, who could very well be their predators. This caring relationship is so effective in terms of getting rid of parasites that it is genetically engrammed in certain types of host fish: after hatching (in the laboratory), they immediately adopt a welcoming pose on their first contact with cleaner wrasses. However, the symbiosis can sometimes turn into parasitism, as once the stock of parasites is exhausted, the cleaners will sometimes simply feed on the mucus or scales of their host, giving the latter a characteristic shock. This balance between symbiosis and parasitism is also found in the African savannas, between oxpecker birds and their herbivorous hosts (antelopes, buffaloes, zebras, giraffes and rhinos), as sometimes the former are no longer satisfied with ticks but start to peck small pieces of flesh.

      Another very specific type of mutually beneficial relationship between species is quite simply domestication. Our species, Homo sapiens, in its recent history, has built very intimate relationships with herbivorous mammals (aurochs that have become cows, wild boars that have become pigs, mouflons that have become sheep, not to mention goats, horses, llamas, elephants and guinea pigs) or with carnivorous mammals (wolves that have become dogs, cats that have remained cats). The relation is simple: food in exchange for protection and reproduction (but without guaranteed well-being). We need simply think of the cat, by far the most abundant feline on the planet: since it was adopted by us, thanks to its appetite for mice, it lets us hunt for food on its behalf …

Domestication is not, however, the prerogative of human beings. Over 30 million years ago, ants began to group aphids into herds in order to milk their secretions of honeydew more easily, and to have a little ‘meat’ from time to time. In exchange, aphids are protected from prowling predators (ladybirds, not wolves), they have shelters built by ants, and are even relieved of their fungal parasites. This relationship is so profitable that it now involves a quarter of aphid species described (1,000 out of 4,000, including a significant number that can no longer live without their ‘shepherdess’ ants).¹⁰

      What about plants? Besides the relationship between pines and firs already mentioned, there are many other collaborations between species. This is the case, for example, with mugwort and tobacco (or barley and thistle), which notify each other of the arrival of herbivores. Once one is bitten by an insect, it emits volatile substances which immediately cause the other one to emit substances that are poisonous for insects.¹¹

       Between dissimilar organizations

      In this last example, the relation between animals (predators) and plants is hardly peaceful. But this is far from a general rule. Plants and animals collaborate very well. Agriculture, which is an example of the domestication of plants by animals, is the typical case of ‘win-win’ interactions between kingdoms.¹²

      People are not the only ones to practise agriculture. At the origin of the apple, for example, there is the bear. On the borders of China and Kazakhstan, bears have carried out a long and valuable process of selection based on a kind of wild apples, small and sour, prized by some birds, gradually giving rise to a sweeter, much larger apple. By some miracle, this part of the world has not been completely deforested, and can today be celebrated as the true cradle of one of the commonest fruits on earth.¹³ The animal beneficiary of the pact has simply changed en route …

In addition to having been the first breeders (of aphids), social insects were also the pioneers of agriculture. This has been extensively described for ants, but less is known about termites, of which 330 species out of the more than 2,600 described¹⁴ make up a compost from plant debris and the droppings of workers to cultivate a fungus which they feed on. The ecological advantage of this feeding method is considerable: we see these species thrive in drier habitats and consume fifteen times more dry matter per hectare than species that do not grow fungi.¹⁵ Another group of insects also cultivates fungi, this time on the walls of the galleries they dig in wood. After 60 million years of this practice,¹⁶ more than half of the 7,500 species of bark beetles, small beetles greatly feared by foresters, have opted for this symbiosis.

      Plants, not at first glance the most