The planet is currently experiencing a rapid loss of biological diversity, an event scientists often refer to as the Sixth Mass Extinction. Unlike the previous five events, which were driven by natural catastrophes like asteroid impacts and volcanic activity, the current crisis is overwhelmingly caused by human influence. The rate at which species are vanishing today is estimated to be dozens to hundreds of times higher than the natural background rate of extinction seen in the fossil record. The loss extends across all classes of life, from charismatic megafauna to obscure insects and fish. Examining the species that have disappeared specifically within the last century provides a look at the scope of this modern-day crisis.
Defining Extinction in the Modern Era
In conservation biology, the term “extinction” carries a precise meaning that dictates how resources are allocated. The International Union for Conservation of Nature (IUCN) classifies a species as “Globally Extinct” (EX) only when there is no reasonable doubt that the last individual has died. This determination requires exhaustive, systematic surveys of known and expected habitats over a period appropriate to the species’ life cycle, confirming its absence.
A species may also be classified as “Extinct in the Wild” (EW). This classification means the species survives only in captivity, such as in zoos, or as a naturalized population well outside its historical geographic range. The distinction between a species being lost forever and one surviving solely under human care is an important measure of conservation status.
High-Profile Mammals and Birds Lost
The most widely recognized losses of the last century often involve highly visible mammals, which serve as poignant symbols of the extinction crisis. The Thylacine, or Tasmanian Tiger (Thylacinus cynocephalus), represents one of the most famous examples, with its last known individual dying in captivity in 1936 in Hobart, Tasmania. This carnivorous marsupial was deliberately hunted to extinction by European settlers who viewed it as a threat to livestock.
More recently, the West African Black Rhinoceros (Diceros bicornis longipes), a subspecies of the black rhinoceros, was declared extinct in 2011. This immense mammal was decimated by rampant poaching for its horn, a product highly valued in some traditional medicine markets. The systematic targeting of the animal for illegal trade proved to be an overwhelming threat to its survival.
Among birds, the status of the Ivory-billed Woodpecker (Campephilus principalis) highlights the challenges of confirming extinction in remote areas. The last universally accepted sighting occurred in 1944 in Louisiana. Its decline was directly linked to the extensive logging of its specialized mature forest habitat in the American South.
Aquatic and Reptilian Species Disappearances
Extinction is not limited to terrestrial megafauna, as aquatic and reptilian species have also vanished within the last 100 years. The Tecopa Pupfish (Cyprinodon nevadensis calidae), a tiny freshwater fish endemic to the hot springs outflows near Tecopa, California, disappeared around 1970. This resulted from the human modification of its isolated desert spring habitat, which mixed the distinct hot and cool springs and introduced non-native fish species.
In the marine environment, the Baiji or Chinese River Dolphin (Lipotes vexillifer) is considered functionally extinct, a status reached around 2002 when extensive surveys failed to locate any individuals. This unique freshwater cetacean was unable to cope with the explosive growth of industrial fishing, boat traffic, and hydroelectric dam construction along China’s Yangtze River.
The Pinta Island Tortoise (Chelonoidis abingdonii), native to the Galápagos Islands, also met its end in the modern era. The last known individual, Lonesome George, died in captivity in 2012. The primary drivers of its decline were overexploitation by whalers in the 19th century and the subsequent introduction of goats to Pinta Island, which destroyed the tortoise’s native vegetation.
Primary Drivers of Recent Species Loss
The causes behind the extinctions of the last century consistently point back to a few overarching human-driven mechanisms.
Habitat Loss and Degradation
Habitat loss and degradation stand as the most significant factor, resulting from the conversion of natural landscapes for agriculture, forestry, and urban development. When forests are cleared or wetlands are drained, species lose the specific conditions required for their survival, leading to population crashes and extinction.
Overexploitation
Overexploitation, which includes unsustainable hunting, fishing, and harvesting, has directly eliminated numerous species, particularly those with commercial value or those perceived as pests. The loss of the West African Black Rhinoceros and the Thylacine are direct consequences of human predation and persecution. This pressure accelerates a species’ decline far beyond its ability to reproduce and recover.
Invasive Species
The introduction of non-native or invasive species also plays a large role, especially in isolated ecosystems like islands and freshwater bodies. These invaders, such as rats, cats, or non-native fish, outcompete native species for food, introduce novel diseases, or act as new predators. The destruction of the Pinta Island Tortoise’s food supply by introduced goats exemplifies how a single foreign species can dismantle an entire ecosystem.