en fighting all day long; male stag-beetles often bear wounds from the huge mandibles of other males" (136). These weapons and shields of animals are as important for victory as swords or spears, are for humans. Sexual selection also involves attracting females by show or aesthetics; some birds as Guiana display their gorgeous plumage and perform strange antics in front of the females, who choose the most attractive partner for them. Darwin believed that "when the males and females of any animal have the same general habits of life, but differ in structure, color, or ornament, such differences have been mainly caused by sexual selection" (137). Darwin illustrates the action of natural selection in various ways. A weak wolf can still survive, if the number of dear increase in its territory. Cats have a tendency to catch rats rather than mice, because that characteristic is inherited is inherited. Even if a slight difference in the habit of an individual can better suit the individual for survival. Darwin says, "if any slight change innate change of habit or of structure benefited an individual wolf, it would have the best chance of surviving and of leaving offspring" (139). Darwin compares natural selection to animal husbandry by saying, " a breeder selects for some definite object, and free intercrossing will wholly stop his work." (148). He explains intercrossing that it affects those animals, which do not breed at a quick rate. Darwin gives a real world example of a breeder, who selects for distinct objects in specie, resulting liberated intercrossing to stop. The "new" animals do not cross with the "inferior" ones. There would be an improvement and alteration in the animal, if many men have the same standard of exactness. As Darwin says "Intercrossing plays an important part in nature in keeping the individuals of the same species, or the same variety, true and uniform in character". (149) Darwin used a daily life example of a nurse...
