Why do elephants change faster than mice?
Compared to small rodents, elephants have a much longer generation period. Nonetheless, palaeontological data indicate that they changed much faster during evolution than, for example, mice. The theory of genetic draft could provide a possible explanation for this. Because of their longer generation period, elephants live in a sort of rapidly changing world. During one generation period of mice (two months) the environment (for example, also the climate) doesn’t change much (this does not apply to cyclic changes related, e.g., to the seasons of the year, but rather to long-term changes to which species react in evolution); however, substantial changes can occur during the generation period of an elephant. Consequently, elephants must adjust to new conditions in each generation and consequently new suitable alleles are quite frequently fixed in their populations. And neutral and only slightly harmful mutations hitchhike along with them; these need not affect the appearance of the elephant but can increase the probability that they will evolve into a new species, see the hypothesis of the formation of reproduction barriers as a consequence of accumulation of incompatible mutations. Other explanations are also possible. For example, large animals usually form small populations; accident plays a more important role (compared to selection) in small populations, so that slightly harmful changes can accumulate more easily and thus faster in these populations. Both these phenomena are employed to explain the paradox of the molecular clock. Although most mutations are formed in copying DNA and thus in cell division during the formation of sex cells, the speed of the protein molecular clock, i.e. the speed of accumulation of mutations in proteins, does not depend on the generation period of the studied organisms. This is a result of the fact that, although fewer (slightly harmful) mutations are formed each year in elephants than in mice, a greater percent of them are fixed in elephants. In accordance with these hypotheses, synonymous mutations behave differently and their accumulation is not proportional to time measured in years but to time measured in generation periods.