The Next Species: The Future of Evolution in the Aftermath of Man (reviewed)

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ichael Tennesen’s 2015 publication, The Next Species: The Future of Evolution in the Aftermath of Man, examines what evolution may have in store for mankind and the earth in the near and distant future. This considerable topic generates numerous questions. What will the future be like for Earth’s plants and animals? How has mankind’s inexorable population growth affected the biomass? Are we truly in the age of the Anthropocene?[1] What is the future of Homo sapiens? Will the next great planetary extinction event also be the end of man? Might another species evolve to compete with or even replace us? Is Earth the only option for the future of man? 

Tennesen’s book explores these questions (and many more) by interviewing scientific experts around the world and weaving those voices into a thoughtful and accessible (if alarming) narrative about extinction and evolution. What is the current state of research suggesting? What might the “aftermath” of man be like? Moreover, are the activities of humans accelerating extinction processes, and if so, is there any way to manage our net impact on the biomass? What final options may be left to the survival of our progeny? Just as the force of extinction events have worked to eradicate whole swathes of species over deep geologic time, so has evolution worked to develop and encourage new species to thrive. Tennesen advances the following questions: “Will nature provide the necessary niches and maneuvers to meet the future? Will the tropics be part of the rescue, if there is one? And will modern man be along for the ride?”[2] 

Humanity’s progress has come as a double-edged sword delivering extraordinary population growth and technological progress, but also irreparable environmental destruction. “Some scientists believe,” Tennesen writes, “that our current situation started at the outset of the Industrial Revolution in Great Britain during the 1700s. This is when CO₂ in the atmosphere began its upward climb…[but] others date the commencement of our dilemma to 1800, when the human population reached one billion.”[3] Typically, the population growth of an organism would be an obvious metric in evaluating its health, success, and sustainability. However, as mankind’s impact of the environment is unprecedented, this meteoric population success may paradoxically be contributing to our own demise, in addition to untold species around the Earth. 

What are some of the immediate challenges to mankind’s recent population growth? If it continues at the current rate from the last fifty years, Tennesen argues, it could reach 27 billion by the end of the century, an unsustainable figure for a host of reasons, foremost of which is that there would not be enough food to feed everyone. This has important implications for growing middle-class consumer societies around that world like China, India, and Brazil. Pointedly, the world’s resources could only support a maximum population of 2 billion if all of those people consumed like present-day middle-class Americans.

Population pressures can also impact the spreading of disease. Hunter-gatherer societies often did not develop immune responses to many communicable diseases because they were typically living in low-density population centers. “It is widely understood,” notes Tennesen, “that you need a certain number of people in close proximity for disease to spread. The critical mass—the point at which the disease achieves optimal virulence and transmissibility—[of measles, for example] is a half million.”[4] As Tennesen's book further explores, the implications for humanity’s growing population—and its attendant consumption of natural resources—has already had a lethal impact of the environment. 

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Many species on Earth do not have to wait for humanity’s population and consumption rates to grow any larger to already be in danger. Twenty thousand species of flora and fauna (that we know of) are at a high risk of extinction. Tennesen cites a study in Nature that concluded that if current rates of extinction continue, “…we would be on track to lose three-quarters or more of all species within the next century.”[5]

Of course, 99.9% of all organisms that have ever existed are extinct.[6] Species have evolved only to later become extinct through the passage of time. As the late comedian George Carlin wryly noted, "we didn't kill them all." There in fact have been five major extinctions over the last 450 million years: Ordovician-Silurian, Late Devonian, Permian-Triassic, Triassic-Jurassic, and Cretaceous-Paleogene. Arguably, we are currently in the sixth, the Holocene Extinction Event. 

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Tennesen lastly explores what other options humanity might have if the earth is no longer habitable. Could our consciousnesses be uploaded to a server and saved for eternity? Could we terraform Mars or Europa, one of Jupiter’s largest moons? If we did colonize another planet or distant moon, after successive generations, would those born there be the same as Homo-sapiens, or a new species having adapted to a new environment? Nature on Earth will survive, adapt, and restore the biomass just as it has done for 450 million years, whether humanity is here to witness it or not. The push of extinction and the pull of evolution have long been the forces shaping life of Earth and will continue on in yet more iterations of extinction events and evolutionary expansions. One must wonder: Is man’s fate to end in extinction, to leave our carbon-based bodies behind and exist digitally in a future-earth, or perhaps even colonize new worlds beyond the solar system?

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[1] The Anthropocene is a term widely [but not universally] used since its coining by Paul Crutzen and Eugene Stoermer in 2000 to denote the present time interval, in which many geologically significant conditions and processes are profoundly altered by human activities (brackets mine, definition from: http://quaternary.stratigraphy.org/workinggroups/anthropocene/).
[2] Tennesen, Michael (2015). The Next Species: The Future of Evolution in the Aftermath of Man. New York: Simon and Schuster, (5).
[3] Ibid., 22.
[4] Ibid., 94.
[5] Ibid., 133.
[6] Tennesen writes: “Extinction in reality is a simple process. It happens when the death rate of a species exceeds the replacement by newborns. This will come for man in five hundred, five thousand, or fifty thousand years as current rates of overpopulation, disease, or other possibilities [nuclear war, asteroid impact, super-volcano].” Ibid., 151.