Frugivory by extinct horses, gomphotheres, ground sloths, and other Pleistocene megafauna offers a key to understanding certain plant reproductive traits in Central American lowland forests. When over 15 genera of Central American large herbivores became extinct roughly 10,000 years ago, seed dispersal and subsequent distributions of many plant species were altered. Introduction of horses and cattle may have in part restored the local ranges of such trees as jicaro (Crescentia alata) and guanacaste (Enterolobium cyclocarpum) that had large mammals as dispersal agents. Plant distributions in neotropical forest and grassland mixes that are moderately and patchily browsed by free-ranging livestock may be more like those before megafaunal extinction than were those present at the time of Spanish conquest.

DNA from excrements can be amplified by means of the polymerase chain reaction. However, this has not been possible with ancient feces. Cross-links between reducing sugars and amino groups were shown to exist in a Pleistocene coprolite from Gypsum Cave, Nevada. A chemical agent, N-phenacylthiazolium bromide, that cleaves such cross-links made it possible to amplify DNA sequences. Analyses of these DNA sequences showed that the coprolite is derived from an extinct sloth, presumably the Shasta ground sloth Nothrotheriops shastensis. Plant DNA sequences from seven groups of plants were identified in the coprolite. The plant assemblage that formed part of the sloth's diet exists today at elevations about 800 meters higher than the cave.

We use national survey data to examine the extent to which various sources of political information expose people to dissimilar political views. We hypothesize that the individual’s ability and desire to exercise selective exposure is a key factor in determining whether a given source produces exposure to dissimilar views. Although a lack of diverse perspectives is a common complaint against American news media, we find that individuals are exposed to far more dissimilar political views via news media than through interpersonal political discussants. The media advantage is rooted in the relative difficulty of selectively exposing oneself to those sources of information, as well as the lesser desire to do so, given the impersonal nature of mass media.

Whatever the cause, it is extraordinary that dozens of genera of large mammals became extinct during the late Quaternary throughout the Western Hemisphere, including 90% of the genera of the xenarthran suborder Phyllophaga (sloths). Radiocarbon dates directly on dung, bones, or other tissue of extinct sloths place their ''last appearance'' datum at Ϸ11,000 radiocarbon years before present (yr BP) or slightly less in North America, Ϸ10,500 yr BP in South America, and Ϸ4,400 yr BP on West Indian islands. This asynchronous situation is not compatible with glacial-interglacial climate change forcing these extinctions, especially given the great elevational, latitudinal, and longitudinal variation of the slothbearing continental sites. Instead, the chronology of last appearance of extinct sloths, whether on continents or islands, more closely tracks the first arrival of people.

Large vertebrates are strong interactors in food webs, yet they were lost from most ecosystems after the dispersal of modern humans from Africa and Eurasia. We call for restoration of missing ecological functions and evolutionary potential of lost North American megafauna using extant conspecifics and related taxa. We refer to this restoration as Pleistocene rewilding; it is conceived as carefully managed ecosystem manipulations whereby costs and benefits are objectively addressed on a case-by-case and locality-by-locality basis. Pleistocene rewilding would deliberately promote large, long-lived species over pest and weed assemblages, facilitate the persistence and ecological effectiveness of megafauna on a global scale, and broaden the underlying premise of conservation from managing extinction to encompass restoring ecological and evolutionary processes. Pleistocene rewilding can begin immediately with species such as Bolson tortoises and feral horses and continue through the coming decades with elephants and Holarctic lions. Our exemplar taxa would contribute biological, economic, and cultural benefits to North America. Owners of large tracts of private land in the central and western United States could be the first to implement this restoration. Risks of Pleistocene rewilding include the possibility of altered disease ecology and associated human health implications, as well as unexpected ecological and sociopolitical consequences of reintroductions. Establishment of programs to monitor suites of species interactions and their consequences for biodiversity and ecosystem health will be a significant challenge. Secure fencing would be a major economic cost, and social challenges will include acceptance of predation as an overriding natural process and the incorporation of pre-Columbian ecological frameworks into conservation strategies.

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The journals of Lewis and Clark reveal a major difference in the taxa, numbers, and behavior of megafauna on either side of the Rocky Mountains in western North America. Two prior events set the stage for what Lewis and Clark would find. The first was the extinction around 13,000 years ago of two-thirds of the native megafauna of the American West. The second was the effects on Indians of deadly new diseases and new technologies brought by Europeans in the post-Columbian era. Populations of large animals, which were preferred prey for native people, were not immune to European influence. Along the Columbia River corridor west of the Rockies, tens of thousands of people lived in a game sink. Here Lewis and Clark's party found too few animals to live off the land by hunting. They adapted poorly to the local diet of fish and roots offered by the Nez Perce and bought dogs and horses to sustain themselves. To the east, uninhabited lands along the Upper Missouri and the Yellowstone rivers supported an abundance of wild game, especially bison, elk, deer, pronghorn, and wolves. This game source occupied part of a buffer zone of 120,000 km 2 probed by various Indian war parties, some of them armed with muskets. William Clark recognized the relationship and near the end of their journey he wrote that they found large numbers of large animals in the land between nations that were at war. Both the abundance of game in buffer or war zones and scarcity of big game in sinks have been misinterpreted as a natural or typical condition. Although efforts to restore ecosystems to what is described in early journals may have merit, they are aimed at a flickering target. Long before these journals were written, the land had been stripped of most of its native megafauna through human influence. In the absence of humans, we predict that much larger populations of bison, elk, deer, and wolves would have ranged the West than were reported in historic documents. Zonas de Guerra y Depresiones de Animales de Caza en el Oeste Americano en Tiempos de Lewis y ClarkResumen: Los documentos de Lewis y Clark revelan una gran diferencia en los números de taxa y la conducta de la megafauna en ambos lados de las montañas Rocallosas del Oeste de Norte América. Dos eventos anteriores establecieron la situación de lo que Lewis y Clark encontrarían. El primero fue la extinción de dos tercios de la megafauna nativa del Oeste Americano, hace alrededor de 13,000 años. El segundo fueron los efectos de las nuevas enfermedades mortales y nuevas tecnologías traídas por los europeos sobre los indios en la era posterior a Colón. Los animales grandes de los cuales la gente nativa dependía no fueron inmunes a la influencia europea. A lo largo del corredor del Rio Columbia al Oeste de las rocallosas, decenas de miles de gentes vivían en una depresión de animales de caza. Aquí el grupo de Lewis y Clark encontró muy pocos animales como para sobrevivir de la caza. Ellos se adaptaron pobremente a la dieta local de peces y raíces ofrecidas por los Nez Perce y compraron per...