Darwin's explanation of evolution remains the central theme of current evolutionary thinking. It has now been assimilated with modern genetics to form what is referred to as neo-Darwinism , in which evolution may be defined as the change in gene frequency in a population over time. In speciation , new species arise when the genetic difference between populations that have been subjected to different patterns of natural selection is sufficiently different to prevent interbreeding between the populations. Two main additional lines of thinking have recently been applied to the evolutionary debate. The first of these seeks to explain the major breaks in the fossil record, such as that at the end of the Cretaceous period which signalled the end of the dinosaurs, by suggesting that long periods of stability have been interrupted by relatively short bursts of rapid evolutionary change, and is referred to as punctuated equilibrium .
Evolution is a major unifying concept in virtually all areas of biology.
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