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Extinctions are a normal part of the evolutionary process, and the background extinction rate is a measurement of "how often" they naturally occur.Normal extinction rates are often used as a comparison to present day extinction rates, to illustrate the higher frequency of extinction today than in all periods of non-extinction events before it.
Permian–Triassic extinction event 252 Ma Large igneous province (LIP) eruptions [ 23 ] from the Siberian Traps , [ 24 ] an impact event (the Wilkes Land Crater ), [ 25 ] an Anoxic event , [ 26 ] an Ice age , [ 27 ] or other possible causes
Operant extinction differs from forgetting in that the latter refers to a decrease in the strength of a behavior over time when it has not been emitted. [6] For example, a child who climbs under his desk, a response which has been reinforced by attention, is subsequently ignored until the attention-seeking behavior no longer
"Behavioral sink" is a term invented by ethologist John B. Calhoun to describe a collapse in behavior that can result from overpopulation.The term and concept derive from a series of over-population experiments Calhoun conducted on Norway rats between 1958 and 1962. [1]
More significantly, the current rate of global species extinctions is estimated as 100 to 1,000 times "background" rates (the average extinction rates in the evolutionary time scale of planet Earth), [71] [72] faster than at any other time in human history, [73] [74] while future rates are likely 10,000 times higher. [72]
With current extinction rates approximated to be 100 to 1,000 times the background extinction rate, [38] it is feared that a de-extinction program might lessen public concerns over the current mass extinction crisis, if it is believed that these species can simply be brought back to life.
The global extinction rate may be approximately 1,000 times higher than the natural background extinction rate. [143] It is estimated that two-thirds of all mammal genera and one-half of all mammal species weighing at least 44 kilograms (97 lb) have gone extinct in the last 50,000 years.
Pseudoextinction (or phyletic extinction) of a species occurs when all members of the species are extinct, but members of a daughter species remain alive. The term pseudoextinction refers to the evolution of a species into a new form, with the resultant disappearance of the ancestral form.