Main directions of evolution

Not all organisms become more complex at the same rate: simple bacteria live alongside complex mammals. The evolutionary success of a group is judged by biological progress or regress. Signs of biological progress: 1) an increase in the number of individuals; 2) range expansion; 3) the appearance of new populations, subspecies and species (insects, bony fish, rodents, flowering plants; in Central Asia the common myna). Signs of biological regress: decline in number, shrinking range, fewer species (for example the desman genus, and ginkgo – only one species survives); it can lead to extinction. According to A. N. Severtsov and I. I. Schmalhausen, progress proceeds in three ways. Aromorphosis is a major change that raises the level of structure and life activity and allows a wide environment to be occupied: photosynthesis, the eukaryotic cell, multicellularity, sexual reproduction, plant tissues, seed and flower, double fertilisation; in animals lungs, the four-chambered heart, warm-bloodedness, live birth and feeding young with milk. Idioadaptation is adaptation to particular conditions that does not raise the level of structure (protective colouring, the varied mouthparts of insects, the variety of bird beaks, fruit dispersal). General degeneration is simplification of structure, often in parasitic or sedentary life: tapeworms have no gut and only very simple sense organs, dodder has no leaves or roots; yet they produce many offspring and can be in progress. After an aromorphosis a period of idioadaptations usually follows. Human activity is putting many species into regress; they are listed in the Red Book.