Paul Schultz Martin (August 22, 1928–September 13, 2010)Mari N. Jensen. . University of Arizona. Retrieved 2010-09-17. was an American geoscientist at the University of Arizona who developed the theory that the Pleistocene extinction of large mammals worldwide was caused by overhunting by humans. Martin's work bridged the fields of ecology, anthropology, geosciences, and paleontology.
Career overview Martin was born in Allentown, Pennsylvania. In 1953, he received his bachelor's degree in zoology from Cornell University. In 1953 and 1956 he completed his master's and doctorate programs at the University of Michigan and then proceeded with postdoctoral research at Yale University and the University of Montreal. Martin's early interest embraced ornithology and herpetology and he conducted extensive fieldwork from 1948 to 1953 in Tamaulipas, Mexico.Martin, Paul S. (1955). Herpetological Records from the Gómez Farias Region of Southwestern Tamaulipas, Mexico. Copeia 1955(3): 173-180.Martin, Paul S. (1955). Zonal Distribution of Vertebrates in a Mexican Cloud Forest. American Naturalist 89: 347-361. He published biogeographies on the birds of the Sierra de TamaulipasMartin, Paul S., C. Richard Robins, and William B. Heed. (1954). Birds and Biogeography of the Sierra de Tamaulipas, an Isolated Pine-Oak Habitat.The Wilson Bulletin.Vol. 66, No. 1: 38-57. and the herpetofauna of the Gómez Farias (= El Cielo) region of Tamaulipas,Martin, Paul S. 1958. A Biogeography of Reptiles and Amphibians in the Gómez Farias Region, Tamaulipas, Mexico. Miscellaneous Publications, Museum of Zoology University of Michigan, 101: 1-102. the latter considered "a classic treatise in historical biogeography".Adler, Kraig. (2012). Contributions to the History of Herpetology, Vol. III. Contributions to Herpetology Vol. 29. Society for the Study of Amphibians and Reptiles. 564 pp. A case of polio, contracted while doing undergraduate field work in Mexico, forced Martin to rely on a cane, which restricted but did not end his field work.Alan Weisman, The World Without Us, p. 68, Picador, 2007 He joined the faculty of the University of Arizona in 1957, maintaining his office (and his ongoing collaborations and regional fieldwork) at the university's Desert Laboratory when he became emeritus professor in 1989. He died in Tucson, Arizona in 2010 at age 82.
Overkill hypothesis
The overkill hypothesis was proposed in 1966 by Martin in a paper published in the journal Nature. Martin wrote, "The chronology of the extinction — first in Africa, second in America, finally in Madagascar — and the intensity of the extinction — moderate in Africa, heavier in America, and extremely heavy in Madagascar ... seems clearly related to the spread of human beings, to their cultural development, and to the vulnerabilities of the faunas they encountered."
Martin theorized that between 13,000 and 11,000 years ago newly arriving humans hunted to extinction North America's Ice Age large mammals, including ground sloths, camels, mammoths and mastodons.Amos Esty, Paul S. Martin. American Scientist. An interview with Paul S. Martin. Retrieved 2010-09-17. The theory, summarized by Martin for a scientific audience in 1973 and in his 2005 book, Twilight of the Mammoths: Ice Age Extinctions and the Rewilding of America, has been controversial and thus widely examined (both criticized and supported) in academic papers. From the outset, Martin pointed to the asynchronous timing of megafaunal extinctions in different locales — especially when paired with time of first arrival of humans. (See the two images at right.) Five years before his death, Martin was still collaborating with colleagues on the timing data. He joined with David W. Steadman and six additional authors in a 2005 paper titled "Asynchronous Extinction of Late Quaternary Sloths on Continents and Islands."
Early critics of the overkill hypothesis were researchers in the field of archaeology (Louis Leakey and Donald Grayson) and the geosciences (Russell Graham). The former focused on disagreements about human capabilities and expansions out of Africa. In geosciences, the focus was on the scale, speed, ecological effects, and biodiversity consequences of climate change during the Pleistocene glacial and interglacial periods. Prior to Martin's overkill idea, the mainstream scientific understanding of the causes of Late Pleistocene extinctions versus the ongoing human-caused Holocene extinction was climate change.
Martin later developed an ancillary hypothesis focusing on the speed of human entry into and saturation of a frontier landscape. This, he called the "blitzkrieg model",Peter D. Ward, The Call of Distant Mammoths, p. 140, Copernicus, 1997 which, similar to the ideas of Russian climatologist Mikhail I. Budyko, relates the sudden demise of large mammal populations on different continents and at different times to the arrival of humans. Martin proposed that as humans migrated from Africa and Eurasia to Australia, the Americas, and the islands of the Pacific, the new arrivals rapidly hunted to extinction the large animals endemic to each continent and thus also naive in the presence of unfamiliar primates equipped with lethal projectiles. Martin particularly focused his research on North America, whose late Ice Age fauna rivaled that of Africa today.Alan Weisman, The World Without Us, pp 68-83, Picador, 2007
For the first several decades of scientific debate about the overkill hypothesis, Martin faced substantial criticism from archaeologists and paleontologists who claimed earlier dates for human arrival in the Americas or later dates for certain extinct animals than the overkill theory would suggest. Martin maintained that such claims were the result of faulty scientific analysis and pointed out that no such dates had yet been independently verified. By 2015, five years after Martin died, radiocarbon dates had been compiled and refined to such an extent that a group of scientists concluded, "Our results, based on analyses of radiocarbon dates from Eastern Beringia, the contiguous United States, and South America, suggest north to south, time, and space transgressive declines in megafaunal populations as predicted by the overkill hypothesis. This finding is difficult to reconcile with other extinction hypotheses."
The overkill hypothesis is thus far less controversial today than it was when first proposed. Overall, when climate is invoked as a causal factor of megafaunal extinctions, it is no longer portrayed as the only cause. For example, in 2010 a paper that focused on the timing of megafaunal extinctions and human occupation within South America concluded, "This pattern suggests that a synergy of human impacts and rapid climate change—analogous to what is happening today—may enhance extinction probability." And in 2012 the authors of a paper published in Nature Communications concluded, "Mammoth extinction was not due to a single cause, but followed a long trajectory in concert with changes in climate, habitat, and human presence."
More than a half century after Martin's first publication on the overkill hypothesis, a new line of evidence emerged that offered strong support. Researchers focusing entirely on genetic analyses of surviving megafaunal populations — rather than paleontological evidence of extinct megafauna — concluded: "The inability of climate to predict the observed population decline of megafauna, especially during the past 75,000 years, implies that human impact became the main driver of megafauna dynamics around this date."
Another unique line of evidence strongly supporting the overkill hypothesis in North America was presented in 2024. A paper was published in Science Advances that had chemically analyzed the skull of an 18 month old child discovered in Montana and dated to 12,800 years ago. Isotopes of carbon and nitrogen attributable to both maternal milk and solid food most closely matched those that would have been found in the mammoth genus and secondarily elk or bison.
Rewilding
Martin also championed the concept of Pleistocene rewilding in which megafauna of the Pleistocene epoch that vanished in North America during the Holocene extinction could be restored by establishing breeding populations of close relatives from other continents. These could include large herbivores, such as llamas, camels, rhinoceros, and elephants, as well as lost carnivores that still reside in Africa: lions and cheetahs.Alan Weisman, The World Without Us, p. 348, Picador, 2007 To restore the megafaunal browsing function lost in North America when its mastodons and mammoths went extinct, "Bring Back the Elephants" was the title of a 1999 advocacy essay that he (with coauthor David A. Burney) published in Wild Earth magazine.
Prior to invention of the term rewilding and the beginnings of advocacy for it by conservation biologists, Martin had already proposed in 1969 and 1970 that large mammal equivalents from Africa and Asia be introduced into western North America. Their ecological function would be to restore native grasslands on which shrubs were becoming dominant — especially where cattle were grazed on semi-arid and arid landscapes in which large carnivores were rare or eliminated. In his 1969 article, Martin proposed reintroducing into North America a dry-adapted browser that had been on this continent for millions of years but vanished after humans arrived. This was the camel. To support his proposal, Martin called upon paleontological evidence that the camel family, Camelidae, actually originated in North America. He also quoted from the journal of an army officer, George Beal, who in 1857 drove a herd of domesticated camels through Texas and Arizona, destined for California. Beal reported that the camels not only would eat plants that cattle could not, but that the camels seemed to prefer thorny shrubs and "bitter herbs." In Martin's 1970 article, his abstract drew upon paleontological evidence of other native species now extinct in North America whose ancestors had evolved millions of years earlier on other continents:"Eleven thousand years ago in North America a major biotic catastrophe resulted in the extinction of 70% of the mammalian megafauna. In the arid Southwest, domestic livestock imperfectly fill the vacated ecological niches. The experimental introduction of modern African animals can be advocated on the grounds that many of the native American mammals were themselves late Pleistocene immigrants from Asia."
In 1992 he published a broader advocacy piece, which blended scientific argument with poetic appeal. Linking the title of his essay, "The Last Entire Earth", to a phrase and sentiment expressed by Henry David Thoreau, Martin followed with:"This, then, is our birthright, a continent whose wilderness once echoed to the thunder of many mighty beasts, a fauna that eclipsed all that remains, including the wild animals of Yellowstone and Denali. Those who ignore the giant ground sloths, native horses, and saber tooth cats in their vision of outdoor America sell the place short, it seems to me. This land is the mastodon's land. While "Home on the Range" commemorates buffalo, deer, and antelope, it misses the mammoth, glyptodonts, and camels."
Evolutionary anachronisms and their ghosts
"Without knowing it, Americans live in a land of ghosts," Paul S. Martin wrote on the first page of his final book,Twilight of the Mammoths (2005), whose subtitle linked "ice age extinctions" with a need for "rewilding of America".