TF写作真题第031套（nt004）

NT_004

In most species of deer, the males have antlers. These bony, branching structures atop the animal’s head begin growing in the spring and continue developing throughout the summer and fall. Starting in late winter the antlers drop off, and the cycle starts all over again in the spring. Why deer grow antlers has long been a source of speculation. Below are three theories about the function of deer antlers.

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.

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.

According to p 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.

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