Frozen Evolution. Or, that’s not the way it is, Mr. Darwin. A Farewell to Selfish Gene.

Periods with higher extinction rates can be classified primarily according to the intensity of extinction, i.e. according to the percentage of species living at the given time in the particular territory that was affected by the elevated rate of extinction.These periods can be further classified according to the size of the territory over which the increased intensity of extinction occurred.In a great many cases, the extinction was of only a local character; however, it has been demonstrated that, in some cases, the extinction was fundamentally global in character and simultaneously affected almost the entire planet (Raup & Jablonski 1993).A further division takes into account the duration of periods of increased extinction.From this viewpoint, we mostly distinguish between pulse extinction, when the actual extinction of most species occurred at practically the same moment, and press extinction, when the individual species tended to die out gradually, probably according to the accumulation of some kind of stress factor in the environment, to which the individual species were variously sensitive (Erwin 1998).The ecological selectivity is an important parameter in which the individual periods of mass extinction differed.Sometimes species living in a certain biotope were primarily affected by extinction; at other times, a wide spectrum of aquatic and terrestrial biotopes were affected.

The possible existence of taxonomic selectivity is also a matter for discussion.It seems that, at least in some cases, extinction primarily affected the members of a certain taxon without regard to the type of habitat occupied by the members of that species or the type of niches in the ecosystem that they occupied.In conclusion, it is necessary to bear in mind that any categorization of extinction is basically artificial and that there are smooth transitions between the two extreme states.