There is also what is called
background extinction, in which species naturally go extinct as a result of natural selection driven by competition.
Climate change is a driving force behind the so-called sixth mass extinction in which species are declining at rates 100 to 1,000 times faster than
background extinction rates.
Wilson now estimates that the rate will reach 10,000 times higher than
background extinction by 2030.
To determine the
background extinction rate, scientists look to the fossil record and to genetic material, or DNA, which accumulates small changes in its sequence as it is copied and passed down from generation to generation.
The few species that seem to disappear in the uppermost Maastrichtian can be interpreted to constitute
background extinction pattern, or can also be interpreted as the remaining Signor-Lipps effect.
Ranging further, the dispute is carried into questions about the
background extinction rate--reflected in the number of species lost before humans arrived.
Even this five-fold increase in
background extinction rates, however, vastly understates the magnitude of the current extinction event because it is derived only from extinction of species known to science.