ON THE EFFECTS OF CROSSING--THE INFLUENCE OF DOMESTICATION ON FERTILITY--CLOSE INTERBREEDING--GOOD AND EVIL RESULTS FROM CHANGED CONDITIONS OF LIFE-- VARIETIES WHEN CROSSED NOT INVARIABLY FERTILE--ON THE DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND VARIETIES--CONCLUSIONS WITH RESPECT TO HYBRIDISM-- LIGHT THROWN ON HYBRIDISM BY THE ILLEGITIMATE PROGENY OF HETEROSTYLED PLANTS-- STERILITY OF CROSSED SPECIES DUE TO DIFFERENCES CONFINED TO THE REPRODUCTIVE SYSTEM--NOT ACCUMULATED THROUGH NATURAL SELECTION--REASONS WHY DOMESTIC VARIETIES ARE NOT MUTUALLY STERILE--TOO MUCH STRESS HAS BEEN LAID ON THE DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND CROSSED VARIETIES-- CONCLUSION. CHAPTER 2.XX.--SELECTION BY MAN. SELECTION A DIFFICULT ART--METHODICAL, UNCONSCIOUS, AND NATURAL SELECTION-- RESULTS OF METHODICAL SELECTION--CARE TAKEN IN SELECTION--SELECTION WITH PLANTS--SELECTION CARRIED ON BY THE ANCIENTS AND BY SEMI-CIVILISED PEOPLE-- UNIMPORTANT CHARACTERS OFTEN ATTENDED TO--UNCONSCIOUS SELECTION--AS CIRCUMSTANCES SLOWLY CHANGE, SO HAVE OUR DOMESTICATED ANIMALS CHANGED THROUGH THE ACTION OF UNCONSCIOUS SELECTION--INFLUENCE OF DIFFERENT BREEDERS ON THE SAME SUB-VARIETY--PLANTS AS AFFECTED BY UNCONSCIOUS SELECTION--EFFECTS OF SELECTION AS SHOWN BY THE GREAT AMOUNT OF DIFFERENCE IN THE PARTS MOST VALUED BY MAN. CHAPTER 2.XXI.--SELECTION, continued. NATURAL SELECTION AS AFFECTING DOMESTIC PRODUCTIONS--CHARACTERS WHICH APPEAR OF TRIFLING VALUE OFTEN OF REAL IMPORTANCE--CIRCUMSTANCES FAVOURABLE TO SELECTION BY MAN--FACILITY IN PREVENTING CROSSES, AND THE NATURE OF THE CONDITIONS--CLOSE ATTENTION AND PERSEVERANCE INDISPENSABLE--THE PRODUCTION OF A LARGE NUMBER OF INDIVIDUALS ESPECIALLY FAVOURABLE--WHEN NO SELECTION IS APPLIED, DISTINCT RACES ARE NOT FORMED--HIGHLY-BRED ANIMALS LIABLE TO DEGENERATION--TENDENCY IN MAN TO CARRY THE SELECTION OF EACH CHARACTER TO AN EXTREME POINT, LEADING TO DIVERGENCE OF CHARACTER, RARELY TO CONVERGENCE-- CHARACTERS CONTINUING TO VARY IN THE SAME DIRECTION IN WHICH THEY HAVE ALREADY VARIED--DIVERGENCE OF CHARACTER, WITH THE EXTINCTION OF INTERMEDIATE VARIETIES, LEADS TO DISTINCTNESS IN OUR DOMESTIC RACES--LIMIT TO THE POWER OF SELECTION--LAPSE OF TIME IMPORTANT--MANNER IN WHICH DOMESTIC RACES HAVE ORIGINATED--SUMMARY. CHAPTER 2.XXII.--CAUSES OF VARIABILITY.