Extinction refers to the permanent termination of an organism by the death of its last member. While extinction is a natural process, the current era, spanning roughly the last 100 years, is marked by a rate of loss far exceeding the historical background rate. This acceleration is directly linked to the rapid expansion and influence of human populations on natural systems. Scientists estimate that the current extinction rate is hundreds, or even thousands, of times higher than the natural average, signifying a profound period of biodiversity loss.
Notable Losses Since 1924
The last century has seen the definitive loss of numerous distinct animal species, driven by human actions and the widespread transformation of environments. These examples span continents and taxonomic groups, illustrating the global reach of the extinction crisis.
The Thylacine (Thylacinus cynocephalus), or Tasmanian Tiger, was one of the largest modern carnivorous marsupials. Once widespread across Tasmania, relentless hunting campaigns, driven by government bounties and perceived threats to livestock, decimated its population. The last known individual died in captivity at the Hobart Zoo in 1936.
The Bali Tiger (Panthera tigris balica) was the smallest tiger subspecies and endemic to Bali. The population was vulnerable to human pressures due to the island’s confined space. The last confirmed individual was shot in 1937, with its extinction resulting from colonial-era sport hunting and the conversion of its forest habitat into agricultural land.
The Paradise Parrot (Psephotus pulcherrimus) of eastern Australia suffered a similar fate, with the last confirmed sighting occurring in 1928. This brightly colored bird was pushed to extinction primarily by habitat degradation, as overgrazing and the cutting down of nesting trees destroyed its grassland environment.
Moving to Africa, the West African Black Rhinoceros (Diceros bicornis longipes) was declared extinct in 2011. Its demise resulted from widespread illegal poaching for its horn, combined with large-scale habitat loss due to industrial agriculture and human settlement expansion.
In the Galápagos Islands, the Pinta Island Tortoise (Chelonoidis abingdonii) became extinct in 2012 with the death of its last known member, Lonesome George. The species was unable to recover from overexploitation by mariners in the 19th century and habitat destruction caused by invasive goats introduced to Pinta Island.
Primary Drivers of Modern Extinction
The majority of modern extinctions are the systemic result of human activities that disrupt natural ecosystems.
The foremost driver of biodiversity loss is the change in land and sea use, which involves converting natural habitats for human purposes. This includes the widespread clearing of forests, wetlands, and grasslands for agriculture, identified as a threat to over 85% of species at risk. This large-scale transformation fragments natural areas, isolating populations and making them genetically vulnerable.
A second significant factor is the introduction of invasive species into new ecosystems, often facilitated by global trade and travel. Non-native organisms, such as predators or pathogens, can devastate local species that have not evolved defenses against them.
Pollution contaminates environments, poisoning wildlife and degrading habitats. This includes chemical runoff from agriculture, industrial waste, and the proliferation of marine plastic, which affects aquatic and seabird species through entanglement and ingestion.
The overexploitation of species through unsustainable hunting, fishing, and harvesting directly reduces populations to unsustainable levels. This pressure is pronounced for large mammals and commercially valuable marine life, where demand outstrips the species’ ability to reproduce and recover.
Compounding these threats is the accelerating impact of climate change, which alters environmental conditions too quickly for many species to adapt. Rising global temperatures, ocean acidification, and altered weather patterns force species to shift their ranges, disrupt food chains, and increase the frequency of catastrophic events.
Defining the Point of No Return
Confirming extinction is a challenging scientific endeavor, as it is nearly impossible to observe the death of the final individual. Conservation bodies, such as the International Union for Conservation of Nature (IUCN), use rigorous criteria to classify a species as Extinct (EX). This classification is applied only when there is no reasonable doubt that the last individual has died. This conclusion is typically reached after exhaustive, species-specific surveys fail to record any signs of the organism across its historical range.
A related category, “Extinct in the Wild” (EW), is used for species that survive only in cultivation, in captivity, or outside their original range. The difficulty in declaring a true extinction is highlighted by “Lazarus species,” which are organisms presumed extinct for decades but are then rediscovered alive. These rediscoveries demonstrate that a lack of sighting does not always equate to permanent loss, underscoring the need for careful, sustained surveying.