Reliable determination of the rate of appearance of new species and extinction of old only according to molecular phylogenetics of modern organisms was impossible, reported in Nature. This approach works only for the evolutionary events that occur now or in the near past, while other cases need to consider at least the paleontological material. Doubt in a purely molecular approach resulted in a long time, but now there is their mathematical justification.
The speed of diversification in the group of organisms depends on how many new species there per unit time (λ) and how many of them died on the same interval (μ). It is easy to calculate, if we know all the types that were of interest to us in Tucson. However, for some groups almost did not find fossil remains, so to reliably estimate their species diversity and its changes in the past only by the paleontological findings impossible.
In 1994 the Oxford biologists proposed to calculate the rate of diversification of these problematic groups in the phylogenetic trees currently existing organisms — schemes, which indicate the relationship of various types in a given group and marked the point when species diverged from a common ancestor. They are built on the basis of molecular data. Know about how fast there are certain mutations in genes, and it allows you to determine the time of divergence of species. Extinction can also affect the hereditary material of organisms. Therefore, theoretically, the phylogenetic trees it is possible to determine the number of species within the taxon, from which some of the modern species and the change of this parameter in time.
Pretty quickly there were doubts in the accuracy of this approach. It needs good work, if λ, μ and their components are constant. But they can change, and the same result can be obtained by substituting different numbers in for the variables. If the number of species, which gave rise to other species, has increased dramatically, to establish the cause of this change will not work: the situation, when existing species became extinct more slowly, and the situation when the new species began to appear faster, will look the same. The same is true for the case when the increase in the number of species whose descendants have survived to the present day, greatly slowed down.
However, the method described in 2004, is used now, and according to molecular phylogenetics of modern organisms even make assumptions about how the climate and other conditions last affected the rate of extinctions. There are mathematical models that allow to determine the increase in the number of species, giving rise to modern organisms, even if λ and μ are not constants.
The Stylianos Luke (Stilianos Louca) and Matthew Pennell (Matthew Pennell) from Canada and the United States tried to describe the change in the number of types, from which existing organisms, and its dependence on data with specific phylogenetic trees of various differential equations. They believed that λ and μ can vary over time and in different models asked differing scenarios of such changes.