A recent analysis has yielded information about the decline of megafauna (giant animals) in modern-day New Zealand. Evolutionary biologists compared DNA from fossils of nine species of moa, large flightless birds that lived for millions of years on the country's South Island. The birds' genetic information suggests that their populations were stable for at least 4,000 years before declining with extreme rapidity only after the arrival of humans on the New Zealand archipelago, 600 years ago.

     In reviewing possible causes for this phenomenon, the scientists dismissed the climatic explanation that accounts for the decline of other megafauna because the extinction happened long after other megafauna had disappeared at the end of the last Ice Age. They ruled out sampling bias because a sample selection impact would not have allowed for the different results observed between the nine species. They rejected the possibility of major impacts by disease or volcanic activity because consistent genetic diversity indicates that no population diminishment occurred prior to the arrival of humans to New Zealand. The lack of population decline prior to human arrival suggests that the moa extinction was caused entirely by human hunting—a hypothesis corroborated by the remains of moa at every life stage found in rubbish piles from the earliest decade of human occupation of the islands. Such evidence leads the researchers to believe that the earliest Polynesian arrivals to New Zealand engaged in indiscriminate hunting of moa and moa eggs because their large size made them attractive as easily obtained food.

     Linguists have offered two explanations describing the origins of language among human populations. Because the use of language is universal among ethno-cultural groups and distinct from any communicative capacity developed elsewhere in the animal kingdom, both explanations assert that the biological evolution of the human organism has exerted some influence on the development of language.

     Proponents of explanation A, or the “continuity theory,” take issue with the suggestion that the development of language occurred fairly suddenly in the course of human evolution. Observations have shown that non-human animals communicate, even in surprisingly complex ways, within kin groups and across species. Human language is incredibly complex and it is difficult to assert that such a complex system could have developed without a long series of evolutionary iterations. Thus it is useful to consider the communication methods of other organisms as analogues to the possible stages of human linguistic development. Scientists have also suggested that human communicative capacities are evolutionary adaptations similar to echolocation among bats or stereopsis among lesser primates: unique abilities particular to the human organism but nonetheless the product of long-form evolutionary processes.

     However, explanation A is not uncontroversial. Critics point out that human language far outstrips the complexity of any known animal communication mechanism and that, therefore, any hypothesis emphasizing iterative development is of limited explanatory utility. They argue that any evolutionary development as unprecedented as human language must have a comparably unprecedented explanation. They support explanation B, “the discontinuity theory,” which can be understood in multiple ways.

     Language, some proponents of explanation B argue, requires an advanced cognitive capacity that pre-human primates (hominids) did not possess. Modern humans achieved language function through the relatively abrupt development of advanced brain anatomy, the “language organ.” This development is supposedly the result of a significant mutation within the human genome. Sudden mutations often have negative effects, making this instance all the more peculiar. Another understanding of the “discontinuity theory” suggests the sudden development of language among human populations is due to a social revolution among early human communities. Even if early human populations had already developed the capacity for language, it went undeveloped until social and cultural factors demanded otherwise. Early human communities can be compared to naturally talented basketball players whose skills go unrecognized until they're scouted by a perceptive coach.

     Scientists have long known that two brain structures lying below the rostrum of the corpus callosum, called septal nuclei (SNs), play a significant role in human pleasure response. This part of the brain interacts with many other elements of the limbic system, which regulates fear expression and other forms of emotional response. Studies show that in some animals, most notably rats, electrical stimulation of SNs can motivate self-stimulation, causing them to perform such behaviors as manipulating levers or returning to regions of their housing that administer further electrical stimulation. Furthermore, connections between the SNs and portions of the brain dedicated to olfaction and memory retention have also been discovered.

     Several other neural structures have been found to play a role in governing the brain's emotional responses, however, not just the SNs of rats and humans. In fact, when laboratory rats had electrical stimulation applied to their habenular nuclei, pleasure responses shifted by 30 percent, whereas the same electrical shock applied to the SNs produced a lesser result. While scientists remain convinced that SNs play a role in the brain's regulation of fear, sadness, joy, and pleasure response, scientists now believe that other neural structures may respond more forcefully to stimulation—even if the voltage of the shock administered doesn't change—than the septal nuclei.

     When Venezuelan-born political leader Simón Bolívar arrived in Europe to pursue his military education when he was a teenager, he arrived at a fortuitous time in world history. What made the time exceptional was Napoleon's 1804 coronation as emperor of France and the wars throughout Europe still ongoing in the wake of the French Revolution, which made the environment ripe for someone determined to achieve freedom, self-determination, and independence from European colonial overlords for the peoples of Latin America.

     Hoping to emulate the revolutionary successes of other colonial societies, many of the countries administered by Spain watched the radical political changes occurring in Europe and North America with longing, even as they continued to be ruled from abroad by foreign elites. The people of Latin America saw their incipient nations exploited for the profit of Madrid, just as they had been for centuries. Summarizing modern historical scholarship, most academics with knowledge of the period argue that the period of revolution in early nineteenth-century Latin America was an inevitable consequence of the dissemination of Enlightenment ideals: a mature society conscious of the prospect of self-rule will almost invariably attempt to bring about that eventuality, by armed means or otherwise.

     Some historians maintain that Bolívar is responsible for the revolutionary circumstances from which he manufactured, in the early years of the nineteenth century, the most momentous set of political changes in Latin American history. But such a narrative only obfuscates the historical trends that had already imbued most Latin American polities with a revolutionary spirit. This spirit did not originate with Bolívar; instead, he served as its focal point and primary agent in world affairs.

     A recent trend lauds the supposedly obvious benefits of locally produced diets and of urban agriculture in particular. These benefits, they say, offer antidotes to pollution, poverty, and illness, and many advocates are urging cities to take action to encourage the growth of food farming in small urban spaces in order to introduce more locally produced food into the market.

     To evaluate these proposals, it is helpful to compare the claims with facts. A central idea of urban agriculturists is that the transportation of non-local food creates pollution. In fact, transportation constitutes a minute percentage of the agricultural sector's greenhouse gas emissions, and the production inefficiencies inherent in farming on small plots could easily erase gains made in transportation. Large rural farms transport production workers and equipment much more efficiently. Moreover, mode of transportation affects the carbon footprint of a meal. The shipment of food over long distances by train or tractor-trailer often consumes less fuel than does transportation more locally using smaller vehicles.

     For urban planners, land use is potentially the most contentious aspect of urban agriculture. Sunlit spaces, especially in the largest and most densely populated cities, often come at a premium. Given the limits on yields and profit margins for food agriculture, costs and benefits must be weighed against those of other businesses in terms of job creation, aesthetic value (since agriculture is a messy business), and scalability (local food's high price limits the market and raises the possibility of saturation). Limited space may be better utilized by housing or retail outlets than by urban gardening.

     It is obvious that there is not enough data on urban agriculture to justify implementation of agriculture-promoting policies within the limits of the largest cities. Many faddish environmental projects in the last two centuries have failed to live up to their promises and subsequently waned, and so might the urban agriculture movement. Meanwhile, the many urban farms currently in operation will have the chance to defy such cynicism, and city governments would do well to allocate resources to those that do.