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主题：鹿角的作用

1. First, some biologists have proposed that the antlers' main function is to help the animal dissipate excess body heat. It is thought that wind blowing through the antlers cools the blood circulating in them. Antlers contain many blood vessels while they are growing, and a large volume of blood can fill them. Consequently, the antlers allow a lot of blood to be cooled by breezes, keeping the animal from overheating.

1. First, if the purpose of the antlers is to cool the animal, then why do deer keep their antlers long after summer is over? Indeed, in some species of deer, the antlers are still growing, getting larger in the winter when there's no need for cooling down. Furthermore, deer, in the hottest regions of the world tend to have the smallest antlers while deer in the cooler regions often have the largest antlers. This pattern doesn't make any sense if the purpose of antlers is to help cool animals.

2. A second theory is that antlers—hard, pointy structures— evolved for defense against predators. Animals that evolved horns, a bony structure similar to antlers, clearly use them in self-defense. Just as bulls and male goats use their horns to combat would-be attackers, deer may use their antlers to defend themselves against animals that try to harm them.

2. Second, if antler served his defense against predators, then we would expect female deer to grow them. After all, only the female deer care for and protect the young. But female deer usually don't have antlers. In fact, we have evidence that deer generally defend themselves in a different way. The main predator of deer in many parts of the United States is the wolf. And a study of wolves showed that wolves often had injuries caused by deer kicking them.

3. According to a third theory, antlers function as a signal used by male deer to communicate their dominance to each other. Specifically, large-size antlers are believed to signal superior strength. According to this theory, males with large antlers are perceived as dominant by males with smaller antlers. Signaling through antlers is supposed to prevent unnecessary fights: according to the theory, when two males confront each other, the one with the smaller antlers will walk away rather than engage in a physical fight against a stronger rival.

3. Third, the idea that antlers serve as a signal of dominance. Well, there have been many observations of male deer confronting each other to establish which one is dominant. The nails face each other, walk up and down in parallel lines, make grunts and other kinds of sounds, and they do this until one of them turns around and walks away. But the result of these confrontations is not determined by antlers’ size. Often, the deer with the bigger antlers walks away without trying to fight. So, it doesn't seem the antlers send a clear signal about dominance.