General characteristics of phylogeny

Phylogeny is the historical development of the living world, while ontogeny is the individual development of one organism from zygote to the end of life. Modern classification rests on relationship between species, that is on phylogeny, which is why it matters. Growth in the number and range of a species or group and the appearance of new subspecies is called biological progress; shrinking numbers and range is biological regress. Biological progress follows three paths: aromorphosis (arogenesis) – a major change that raises overall organisation and life activity, for example photosynthesis, multicellularity, sexual reproduction, the four-chambered heart, warm-bloodedness, the seed and the flower; idioadaptation (allogenesis) – a specific adaptation to a particular environment without a general rise in organisation, for example the various shapes of bird beaks; general degeneration (catagenesis) – simplification of structure, for example the loss of gut and sense organs in a parasitic tapeworm. Even if simplified, parasites may be numerous thanks to high fertility, so they too are on the path of biological progress.