| Darwin, who viewed natural selection as a process producing slow anagenetic changes along lines of descent, thought that species were arbitrary slices. |
| Species defined in these anagenetic terms have neither discrete temporal boundaries nor a sufficient level of constancy during their evolutionary tenures. |
| Assigning species names within an anagenetic lineage is problematic. |
| In the first case, i.e. a new anagenetic evolutionary trend, a complete reversal of the direction of natural selection should be assumed. |
| Most of these anagenetic changes are probably concentrated only within the earliest period of the existence of a new species. |
