Biologist Rowan Hooper highlights the critical role of symbiosis—the cooperative interaction between different species—in the development and sustainability of life on Earth. In his recent book, Hooper challenges the traditional evolutionary narrative that has often emphasized competition as the primary force shaping natural selection, arguing instead that cooperation has been fundamental to life’s proliferation over billions of years.

While Charles Darwin’s work is commonly associated with the idea of competition driving evolution, Hooper points out that Darwin also acknowledged the interconnectedness of life. He quotes Darwin’s recognition that “Life... depends on other life” and stresses the complex relationships binding plants, animals, and microorganisms within ecosystems.

To illustrate symbiosis, Hooper cites several examples. One straightforward instance occurs in legumes, such as beans, whose roots develop nodules containing rhizobia bacteria. These bacteria convert nitrogen from the atmosphere into a form that plants can use as fertilizer, enabling their growth in nitrogen-poor soils. Without this bacterial partnership, these plants would struggle to survive.

Hooper also describes a symbiotic relationship observed in Tanzania between the whistling-thorn tree and a species of ant. The tree provides the ants with nectar and shelter, while the ants aggressively defend the tree from herbivores, including large animals such as elephants. Hooper recounts experiencing the ants’ defensive behavior firsthand, as they swarmed and bit when he touched the tree.

Humans themselves are described as “mobile ecosystems,” hosting trillions of microorganisms that influence health and even behavior. For instance, up to 95% of serotonin—a neurotransmitter affecting mood—is produced by gut microbes, demonstrating the profound impact of symbiotic relationships on human physiology and psychology. Hooper references the 2017 book *The Psychobiotic Revolution*, noting its assertion that emotions ranging from joy to anxiety are linked to gut bacteria.

Hooper contends that symbiosis is not only foundational to the origin and evolution of life but also crucial to its ongoing functioning. He warns that a worldview focused solely on competition has contributed to environmental degradation and the brink of ecosystem collapse. Instead, he advocates for recognizing the interconnectedness and mutual dependencies that enable life to thrive, suggesting that understanding these relationships is essential for ecological stability and sustainability.