Human Causes of Extinction

Most extinctions today are caused, directly or indirectly, by human activity. The main causes are:Habitat destruction: the greatest threat. Forests, wetlands and grasslands are cleared for farming, logging, mining and building. For example, clearing rainforest in Borneo and Sumatra for oil palm plantations threatens orangutans.Over-exploitation: hunting, fishing and collecting faster than species can reproduce. The passenger pigeon, once the most numerous bird in North America with billions of individuals, was hunted to extinction; the last one died in 1914. Poaching for ivory, rhino horn and traditional medicines threatens elephants, rhinos and pangolins.Introduced species: species moved to new areas, deliberately or accidentally, may prey on or out-compete native species. Island species that evolved without predators are especially vulnerable. The dodo of Mauritius had died out by the late 17th century, because of hunting and introduced rats, pigs and monkeys that ate its eggs.Pollution: pesticides such as DDT accumulated along food chains and thinned the eggshells of birds of prey; oil spills, plastics and eutrophication kill aquatic life.Climate change: species unable to move or adapt fast enough may die out, especially those on mountains, in polar regions or on islands.Disease: introduced pathogens such as the chytrid fungus have caused declines and extinctions of many amphibians worldwide.These factors often act together: habitat fragmented by farming leaves small populations that are easily finished off by hunting, disease or a changing climate.