Half-Earth: Our Planet’s Fight for Life

Wilson focuses this chapter on the incredible diversity seen in microorganisms, starting with the human body and ending with the deep biosphere. DNA sequencing has revealed that human bodies, like other animals and plants, harbor millions of microorganisms, such as bacteria and archaea. The genetic material of these microorganisms is known as the microbiome. Most of these microorganisms are considered “mutualistic symbionts” (121), meaning that the microorganism and human host work together in a mutually beneficial relationship. Microorganisms help protect the human body from bad bacteria and aid in digestion and waste disposal. However, like other ecosystems, a microbiome can become imbalanced, leading to health problems such as obesity and diabetes.

Since the origin of life, microorganisms have dominated in terms of numbers and their distribution across the planet. Robert Kolter, a microbiologist, described the biosphere as having “shaped by an invisible world” (124). However, these are the least understood of all species. Wilson provides three reasons for this lack of understanding. The first is that bacteria are highly promiscuous. While most organisms get their genes from their parents, bacteria can steal genes from the environment. Many also lay dormant in microbial seed banks and only begin to multiply when “the environment changes to suit its DNA-coded preference” (125). Advances in DNA technology have also allowed scientists to see, for the first time, bacteria that were too small for conventional light microscopy. The bacteria Prochlorococcus, according to Wilson, are the most important of these organisms discovered so far. They are the most common organism in warm ocean waters. Research has also revealed that they are prey for even smaller viruses in the ocean.

Wilson notes that microorganisms also thrive in the deep biosphere, which is the part of the biosphere that extends several kilometers below the continental shelf. Microbes that live here “comprise more than half of all microorganisms on the planet” (129). To Wilson, the existence of the deep biosphere requires a fundamental shift in how we view biodiversity. If the surface of the planet were destroyed, life would likely continue in the deep biosphere. Wilson ends this chapter by positing that, after millions of years, the organisms of the deep biosphere might eventually reach the surface and evolve to other multi-celled organisms, including something human-like.

This chapter summarizes Wilson’s request to 18 senior naturalists to provide him with the best nature reserves in the biosphere. Wilson asked that recommendations be based on “richness, uniqueness, and most in need of research and protection, in other words those you most care about” (136). The “best places in the biosphere” comprise a variety of environments, such as rainforests, grasslands, mountains, forests, wetlands, archipelagos, islands, and even entire countries (136). Human population is low in all these places.

The list includes the redwood forests of California, the Madrean pine-oak woodlands of Mexico and the southwestern United States, Cuba and Hispaniola (West Indies), the Amazon River Basin, the Guiana Shield (Guyana, Suriname, and French Guiana), Tepuis (Venezuela and western Guyana), the Greater Manú region of Peru, the cloud and summit forests of Central America and the Northern Andes, Páramos (South America), the Atlantic Forest of South America, the Cerrado (east-central Brazil), the Pantanal (southern Brazil and extending into Bolivia), the Galápagos (archipelago west of the Ecuadorian mainland), the Białowieża Forest (Poland and Belarus) and Lake Baikal (Russian Siberia), the Christian Orthodox church forests (Ethiopia), Socotra (island in the Indian Ocean), the Serengeti grasslands (northern Tanzania to southwestern Kenya), Gorongosa National Park (Mozambique), South Africa, the forests of the Congo Basin, the Atewa Forest (Ghana), Madagascar, the Altai Mountains (Central Asia), the Western Ghats of India, Bhutan, Myanmar, the scrubland of Southwestern Australia, the Gibber Plains (Australia), New Guinea, New Caledonia, the McMurdo Dry Valleys (Antarctica), and Hawaii.

This list is not the same as the global biodiversity “hot spots,” a list that focuses on areas with large concentrations of endangered species; rather, it highlights areas with rich biodiversity that can and must be conserved. As Wilson notes, “almost all of these last domains of the natural living environment are under some degree of threat or other, but they can be saved for future generations if those alive today have the will to act on their behalf” (135).

Each species has its own history and is “the inheritor of an ancient lineage” (155). All living species have the same primordial ancestor. Scientists work to reconstruct the evolutionary relationships of species, placing those that are more closely related on a phylogeny. These “evolutionary family trees” allow for a better understanding of the history of life and the current natural world (156).

Humans, like other species, have their own evolutionary history, but ours is a product of culture and biology. A unique adaptation “is our relatively powerful minds” (157), which allow us to “accumulate knowledge for its own sake” and “make decisions for the future” (157). To Wilson, it is these traits that have driven our desire to understand the natural world. The digital revolution has improved these scientific studies, making much of the biodiversity literature accessible through platforms such as the Biodiversity Heritage Library and the Encyclopedia of Life. Wilson laments that a major problem in the study of global biodiversity is the lack of expert scientific naturalists. He ties this issue to lack of funding and prestige for natural history compared to other biological disciplines, resulting in fewer individuals pursuing careers in natural history. This situation “is a loser for science and for humanity’s ability to protect the living environment” (166).