Query: Each year sees the disappearance of thousands of plant and animal species which we will never know, which our children will never see, because they have been lost for ever.

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Human overpopulation <=SEP=> Human overpopulation occurs when the ecological footprint of a human population in a specific geographical location exceeds the carrying capacity of the place occupied by that group . Overpopulation can further be viewed , in a long term perspective , as existing when a population can not be maintained given the rapid depletion of non-renewable resources or given the degradation of the capacity of the environment to give support to the population .   The term human overpopulation refers to the relationship between the entire human population and its environment : the Earth , or to smaller geographical areas such as countries . Overpopulation can result from an increase in births , a decline in mortality rates , an increase in immigration , or an unsustainable biome and depletion of resources . It is possible for very sparsely populated areas to be overpopulated if the area has a meagre or non-existent capability to sustain life ( e.g. a desert ) . Advocates of population moderation cite issues like quality of life , carrying capacity , and risk of starvation as a basis to argue against continuing high human population growth and for population decline . Scientists suggest that the human impact on the environment as a result of overpopulation , profligate consumption and proliferation of technology has pushed the planet into a new geological epoch known as the Anthropocene .

Extinction <=SEP=> In biology and ecology , extinction is the end of an organism or of a group of organisms ( taxon ) , normally a species . The moment of extinction is generally considered to be the death of the last individual of the species , although the capacity to breed and recover may have been lost before this point . Because a species ' potential range may be very large , determining this moment is difficult , and is usually done retrospectively . This difficulty leads to phenomena such as Lazarus taxa , where a species presumed extinct abruptly `` reappears '' ( typically in the fossil record ) after a period of apparent absence .   More than 99 percent of all species , amounting to over five billion species , that ever lived on Earth are estimated to be extinct . Estimates on the number of Earth 's current species range from 10 million to 14 million , of which about 1.2 million have been documented and over 86 percent have not yet been described . More recently , in May 2016 , scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described .   Through evolution , species arise through the process of speciation -- where new varieties of organisms arise and thrive when they are able to find and exploit an ecological niche -- and species become extinct when they are no longer able to survive in changing conditions or against superior competition . The relationship between animals and their ecological niches has been firmly established . A typical species becomes extinct within 10 million years of its first appearance , although some species , called living fossils , survive with virtually no morphological change for hundreds of millions of years .   Mass extinctions are relatively rare events ; however , isolated extinctions are quite common . Only recently have extinctions been recorded and scientists have become alarmed at the current high rate of extinctions . Most species that become extinct are never scientifically documented . Some scientists estimate that up to half of presently existing plant and animal species may become extinct by 2100 .   A dagger symbol next to a species name is often used to indicate its extinction .