Costly Signals
阅读材料
Costly Signals
Animals typically choose mates that they judge to be physically fit or strong and thus more likely to produce strong, healthy offspring. One way that animals make this judgment about strength is based on appearance. This has led to the evolution of costly signals. Costly signals are physical signs or indications that an animal makes to communicate to potential mates that it is especially strong. However, the animal makes this signal at a risk or cost because it may make the animal more likely to be attacked by predators. The fact that the animal is more vulnerable to attack but is still able to escape and survive dangerous situations shows the animal's strength.
听力材料
So a classic example of this is the peacock's tail. The males of this bird species, as you may know, have these huge, extravagant tails with long, brightly colored feathers. And they display these tails when they're looking for a female to breed with. They walk around showing off their feathered tails to attract female peacocks attention since the females are interested in males with big, colorful tails. Well, the thing about these large, magnificent tails is they make it harder for the male peacocks to move, since they have to drag the weight of these big tails behind them when they walk, run or fly, and the tail is heavy, it's a burden. So it slows them down and makes it harder for them to get away from tigers and other threatening animals they might encounter. So to the female peacocks, it's particularly impressive when the males have these big, heavy tails and can still escape tigers and move around and flee quickly when they need to. And this is partly why the peacock's tails have come to be so large and colorful over time, even though they weigh the birds down.
问题
Explain how the example from the lecture illustrates the concept of costly signals.
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基础版
The concept of costly signals refers to physical traits that demonstrate an animal's strength but also come with risks.
The professor uses peacocks as an example. Male peacocks have large, colorful tails that attract females. However, these tails are heavy and make it harder for them to move quickly, increasing their risk of being caught by predators like tigers.
This illustrates costly signals because, first, the tail is a sign of strength—females prefer males with big tails because only strong peacocks can survive despite the disadvantage. Second, there is a real cost—the tail slows them down, making escape more difficult. Thus, the peacock’s tail is a perfect example of how animals evolve traits that are both attractive and risky.
高分版
Costly signals are physical traits that evolve because they effectively advertise an animal’s fitness, despite imposing survival risks.
The professor’s peacock example vividly demonstrates this concept. Male peacocks possess extravagant, brightly colored tails that serve as a courtship display. While these tails enhance mating success by signaling genetic quality to females, they simultaneously hinder mobility—making the males slower and more vulnerable to predators like tigers.
This exemplifies costly signals in two key ways. First, Evolutionary trade-off—The tail’s size and brilliance prove the male’s exceptional fitness, as only the strongest individuals can afford such a handicap and still evade predators. Second,Sexual selection reinforcement—Females preferentially select males with the most burdensome tails because their survival despite this disadvantage reliably indicates superior genes. Ultimately, this explains why peacock tails became increasingly elaborate over time—the reproductive advantage outweighs the survival cost. -
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