28/06/2018

'Darwin wasn't wrong, but his perspective was childish.'

Reproduction from the IMPA Science & Mathematics blog, published in O Globo, and coordinated by Claudio Landim.

Bernardo Araújo , Laboratory of Ecology and Conservation of Populations – (UFRJ)

"Thus, it is from the war of nature, from hunger and death, that the highest goal we are capable of conceiving, the production of superior animals, arises"; and from this powerful passage comes the conclusion of the most important book in the history of biology. With *On the Origin of Species*, Charles Darwin presented the world with the concept of natural selection, turning the eyes of science towards a new horizon. But it wasn't only the eyes of scientists that were captivated by the descriptions of the "struggle for existence" brought by the English naturalist. The maxim of "survival of the fittest" still adds red to the green that most people see in nature. This concept fills the popular imagination with images of fragile prey pursued by voracious predators, of beasts entangled in bloody battles for territory. It gives life to art such as that of George Bouverie Goddard and William Robinson Leigh, and makes us believe that the natural world is organized around violence. Reality, however, has many more colors, which become clear under canopies that should be familiar to us all.

Walking among the trees of a forest, we can be deceived by the play of light and shadow on the ground and by the unwavering wooden pillars that envelop us in a timeless atmosphere, as if we were entering a temple. But in reality, these ecosystems are constantly changing. Trees die, saplings are born, and over decades clearings are filled, species change places, new forests emerge, disappear, expand and shrink. And what governs this dynamic is not a relationship of teeth and claws. The forest is not a coliseum. The forest is a great bazaar.

High in the treetops, where the trees display vibrant flowers in color and aroma, bees, wasps, hummingbirds, small bats, and various other animals pass by, enchanted not by the exuberant display, but by what it signals. These small creatures feed on pollen and nectar, drawing part of their sustenance from the flowers. Plants expend a good portion of their energy creating these delights (more than 40% in some species), but not for the benefit of their visitors. Every time an animal touches a flower to feed, some of the pollen produced by it sticks to its body and is transported to the next flowers visited. Pollen grains are essentially gametes, and upon contact with the ovary present in neighboring flowers, they initiate the formation of an embryo – a seed. In this way, all the small creatures thirsty for food are recruited for a great reproductive ritual. Trees have the benefit of a transport system they cannot perform on their own. In return, the animals can feast on the carbohydrates and proteins necessary for their survival.

The cycle continues. The now-formed seed is enveloped by a showy and nutritious layer, seeking to entice new customers: the fruit. Birds like toucans, jacutingas, and araçaris, as well as marmosets, capuchin monkeys, and howler monkeys, rush to feast on the fruits on the branches. Tortoises, tapirs, pacas, and curassows go after ripe fruits fallen under the mother plants. Once again, while feeding, these creatures are providing an important service to the trees, as they also swallow their future offspring. Walking and flapping their wings away, these animals will eventually defecate the ingested seeds. This movement is crucial, because without it the small seedlings would develop close to their siblings and their mother. This accumulation attracts predators and diseases, not to mention that trees of the same species require the same nutrients from the soil, causing the new generation to live in constant competition with its immediate family. Few young seedlings would survive to become adult trees.

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